layout editor: in-between split buttons sit above the divider handle; doc nits

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -5,8 +5,9 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 ## What this project is
 
 udpscope is a **GTK4 oscilloscope-style viewer for a UDPStreamer source**. It receives one
-UDP stream with `deps/udpsclient`, buffers it in a large ring (default 200 MB), and draws it
-with `deps/plotter` — a figure of up to eight stacked rows sharing one x window. On top of
+data source -- a UDPStreamer stream through `deps/udpsclient` by default, or another registered
+source kind (see `docs/claude/architecture.md`) -- buffers it in a large ring (default 10 M samples per signal, under an 8 GiB memory limit), and draws it
+with `deps/plotter` — a figure of up to eight plots in stacked rows (a row can be split into up to four side by side) sharing one x window. On top of
 the live view it provides the things a bench scope provides: a trigger with a pre/post event
 window, a pause that freezes the visible window, cursors, statistical measurements,
 user-defined math channels built in a node editor, and an export of the visible window to
@@ -18,9 +19,14 @@ Two documents bound the work and are **not** interchangeable with this one:
 - **`README.md`** documents what was actually *built*, including deliberate deviations from
   the spec and known limitations. **Read it before concluding something is a bug.**
 
+**Deliberate deviation from `SPECS.md` line 1:** the sample buffer is budgeted in *samples per signal*
+(`--buffer-samples`, rounded down to a power of two), not in megabytes, under a separate hard
+`--memory-limit-mb` (also a Preferences row). There is no `--buffer-mb`; see README and `SPECS.md`'s
+"Deviations from the spec".
+
 Three things shape almost every change here, and the linked files expand on each:
 
-- **There are exactly two threads** — a producer that owns the UDP client and the GTK main
+- **There are exactly two threads** — a producer that owns the data source and the GTK main
   thread that owns every widget and the GL context — and they share `ScopeModel` under one
   mutex. Samples cross through lock-free rings, never through the lock.
 - **There is no unit test suite.** The only automated check is the application's own headless
@@ -38,26 +44,26 @@ The detail lives in `docs/claude/`. Read the files that touch the area you are e
 | File | What it covers |
 | --- | --- |
 | [build-and-run.md](docs/claude/build-and-run.md) | Configuring and building, the desktop-entry target, the command-line options, and the two vendored dependencies (`deps/plotter`, `deps/udpsclient`) including what was changed upstream and why. |
-| [verification.md](docs/claude/verification.md) | How to run the headless self-check, the **two baselines every run is read against** (exactly four build warnings; no `Gtk-CRITICAL`), and the environment variable that schedules each probe. |
+| [verification.md](docs/claude/verification.md) | How to run the headless self-check, the **two baselines every run is read against** (exactly one build warning; no `Gtk-CRITICAL`), and the environment variable that schedules each probe. |
 | [probe-readings.md](docs/claude/probe-readings.md) | The per-line reference for the self-check's output: what every probe and dump line means, the value it must read, and the defect a wrong reading names. |
 
 ### How the application is put together
 
 | File | What it covers |
 | --- | --- |
-| [architecture.md](docs/claude/architecture.md) | The two threads and what they share; the one `BufferStore` and the four display modes (`Live`, `Capturing`, `Held`, `Waiting`); the display clock and `stream_at_x0()`; the layers to keep straight (`SignalInfo` → `ChannelBuffer` → `SlotSeries` → `RowSet`). |
+| [architecture.md](docs/claude/architecture.md) | The two threads and what they share; the one `BufferStore` and the four display modes (`Live`, `Capturing`, `Held`, `Waiting`); the display clock and `stream_at_x0()`; the layers to keep straight (`SignalInfo` → `ChannelBuffer` → `SlotSeries` → `RowSet`); the source plugins; the window's chrome (slide-over, badge bar, dock) and when each is built. |
 
 ### Invariants worth knowing before editing
 
 | File | What it covers |
 | --- | --- |
-| [invariants-plot-and-layout.md](docs/claude/invariants-plot-and-layout.md) | What `plot::Figure`/`plot::Plot` can and cannot be asked to do, what a row's contents belong to, the layout editor's overlay children, and the rule that **layout must not depend on content**. |
+| [invariants-plot-and-layout.md](docs/claude/invariants-plot-and-layout.md) | What `plot::Figure`/`plot::Plot` can and cannot be asked to do, what a row's contents belong to, the layout editor's and the slide-over's overlay children (with the pick rule), the badge bar's fixed height, and the rule that **layout must not depend on content**. |
 | [invariants-readouts-and-cursors.md](docs/claude/invariants-readouts-and-cursors.md) | A readout quotes a stored sample and never a value between two; how the cursors are read back from the plots; the one formatter both panes share. |
 | [invariants-data-path.md](docs/claude/invariants-data-path.md) | What rebuilds the buffer and drops history, why decimation at ingest is an **average** and never a stride, and the two rules the `f64` time ring and its cached first stamp impose. |
 | [invariants-rendering.md](docs/claude/invariants-rendering.md) | How the renderer maps a visible range onto samples (never the `dx()` grid), what `gather()` emits and relative to which origin, why every series needs a real `MinMaxPyramid`, and why a dense trace is drawn one pixel column at a time. |
 | [invariants-trigger-and-pinning.md](docs/claude/invariants-trigger-and-pinning.md) | The event window counted in stream seconds end to end, what pins an axis in each mode, and what each pin is measured *from* (the snapshot's own stamps, not the request). |
 | [invariants-time-axis-and-window.md](docs/claude/invariants-time-axis-and-window.md) | **No plot interaction changes the time scale**; `apply_time_window()` is the only path that does; how the x labels pick their form; what a fit restores. |
-| [invariants-measurements.md](docs/claude/invariants-measurements.md) | Why the pane is refreshed on a cadence, why neither pass may read its window raw, and how a crossing is counted with hysteresis. |
+| [invariants-measurements.md](docs/claude/invariants-measurements.md) | Why the pane is refreshed on a cadence, why neither pass may read its window raw, how a crossing is counted with hysteresis, and which mean over a split is which. |
 | [invariants-math-channels.md](docs/claude/invariants-math-channels.md) | A math channel *is* a channel; the engine runs on the producer thread, so a regression there costs packets and not frames; the node editor's own rules. |
 | [invariants-session-and-export.md](docs/claude/invariants-session-and-export.md) | What a session file persists and in what order, when a save is refused, and when an export is collected. |
-| [invariants-gtk-and-chrome.md](docs/claude/invariants-gtk-and-chrome.md) | The GTK signal-signature and dialog-lifetime traps this app has already fallen into, the status bar's two tiers, the six bundled icons and their authoring rules, and the help pages. |
+| [invariants-gtk-and-chrome.md](docs/claude/invariants-gtk-and-chrome.md) | The GTK signal-signature and dialog-lifetime traps this app has already fallen into, the status bar's two tiers, the bundled icons and their authoring rules, how the slide-over's click-away coexists with the plot's gestures, how the guided tour opens a page, and how the Mallard manual is opened. |

CMakeLists.txt

@@ -11,6 +11,8 @@ if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
 endif()
 
 find_package(Threads REQUIRED)
+# `CMAKE_INSTALL_DATADIR` (the `share` under the prefix) for the help set's install path.
+include(GNUInstallDirs)
 
 # --- libadwaita: the shortcut overview ---------------------------------------
 # GTK4's own `GtkShortcutsWindow` is deprecated as of 4.18 and libadwaita's
@@ -61,21 +63,72 @@ add_custom_command(
   COMMENT "Compiling udpscope icon resources"
   VERBATIM)
 
-# --- help pages: Pango markup in a GResource ----------------------------------
-# A second bundle beside the icons'. --c-name is given explicitly so the two generated
-# sources cannot collide on symbol names.
-set(UDPSCOPE_HELP_DIR ${CMAKE_CURRENT_SOURCE_DIR}/src/help)
-file(GLOB UDPSCOPE_HELP_FILES CONFIGURE_DEPENDS ${UDPSCOPE_HELP_DIR}/*.txt)
-add_custom_command(
-  OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/udpscope_help_resources.c
-  COMMAND ${GLIB_COMPILE_RESOURCES}
-          --target=${CMAKE_CURRENT_BINARY_DIR}/udpscope_help_resources.c
-          --sourcedir=${UDPSCOPE_HELP_DIR}
-          --c-name=udpscope_help
-          --generate-source
-          ${UDPSCOPE_HELP_DIR}/udpscope-help.gresource.xml
-  DEPENDS ${UDPSCOPE_HELP_DIR}/udpscope-help.gresource.xml ${UDPSCOPE_HELP_FILES}
-  COMMENT "Compiling udpscope help resources"
+# --- the manual: a Mallard help set, installed for the `help:` URI ------------
+# The manual is no longer a GResource compiled into the binary. It is a Mallard set that the
+# desktop help viewer (Yelp on GNOME) reads off disk, because that is the only way `F1` can
+# open a real, searchable, translatable document and the only way the freedesktop Help System
+# Specification's `help:` URI resolves it. The user documentation is then *files*, checked and
+# installed rather than compiled in.
+#
+# The document identifier -- the `<name>` in `help:<name>` -- is derived from the desktop
+# file's own basename (its desktop-file id), not written out twice: the same string is the
+# `.desktop` file, the GApplication id and the installed directory. The specification installs
+# a document at `<datadir>/help/<lang>/<document>/` and resolves `help:<document>` to the first
+# match under $XDG_DATA_HOME/$XDG_DATA_DIRS, so the directory name *is* the identifier.
+# NAME_WE is not used: it strips the *longest* extension, so it would cut `org.udpscope.app`
+# down to `org`. Strip the two suffixes this one file actually carries, in order.
+get_filename_component(_udpscope_desktop
+  ${CMAKE_CURRENT_SOURCE_DIR}/data/org.udpscope.app.desktop.in NAME)
+string(REGEX REPLACE "\\.desktop\\.in$" "" UDPSCOPE_HELP_NAME "${_udpscope_desktop}")
+unset(_udpscope_desktop)
+set(UDPSCOPE_HELP_SRC ${CMAKE_CURRENT_SOURCE_DIR}/help/C/${UDPSCOPE_HELP_NAME})
+file(GLOB UDPSCOPE_HELP_FILES CONFIGURE_DEPENDS
+     ${UDPSCOPE_HELP_SRC}/*.page ${UDPSCOPE_HELP_SRC}/figures/*.png)
+
+# The install rule the specification asks for. `CMAKE_INSTALL_DATADIR` is `share` by default,
+# so the set lands at `<prefix>/share/help/C/<document>/`, which is exactly where a viewer
+# looks. There is no install step for the binary itself (see the desktop-entry target below),
+# but the manual is *read from a datadir* by another process, so it has to be installable.
+#
+# `COMPONENT Help` is what lets the opt-in targets below install *only* the manual: it names this
+# rule, and `cmake --install --component Help` runs it and nothing else. The ordinary
+# `cmake --install` installs every component, so its behaviour is unchanged -- the component is a
+# filter a caller may apply, not a change to the default.
+install(DIRECTORY ${UDPSCOPE_HELP_SRC}/
+        DESTINATION ${CMAKE_INSTALL_DATADIR}/help/C/${UDPSCOPE_HELP_NAME}
+        COMPONENT Help
+        FILES_MATCHING PATTERN "*.page" PATTERN "*.png" PATTERN "*.jpg")
+
+# --- installing the manual alone: prefix-wide and user-local, both opt-in -----
+# A user who runs the binary out of a build tree wants *just* the manual where `help:` resolves,
+# and not the `cmake --install` of a whole project. These two targets are that, one per
+# destination; neither is built by default and neither is touched by `cmake --build build`.
+#
+# `install-help` honours `CMAKE_INSTALL_PREFIX`, so a packager or a system-wide user points it at
+# `/usr` with -DCMAKE_INSTALL_PREFIX at configure time. It goes through the install machinery
+# (`cmake --install`) rather than a hand-rolled copy, which is what makes DESTDIR and `--prefix`
+# behave exactly as they do for the ordinary install. It cannot install system-wide on its own:
+# `/usr` is root-owned, so the target writes to the configured prefix and a system-wide caller
+# wraps it in `sudo` -- a build target has no more privilege than the shell that runs it.
+add_custom_target(install-help
+  COMMAND ${CMAKE_COMMAND} --install ${CMAKE_BINARY_DIR} --component Help
+  COMMENT "Installing the manual into ${CMAKE_INSTALL_PREFIX}"
+  VERBATIM)
+
+# `install-help-user` is the no-root case the launch-failure alert names. It resolves the user
+# data directory the way `help_installed_path()` does -- `$XDG_DATA_HOME` when it is set,
+# `$HOME/.local/share` otherwise, the XDG Base Directory Specification's own default -- and copies
+# the set there. The copy is done by a script rather than by `cmake --install --prefix` because
+# the destination is the *data directory*, not a prefix: `cmake --install`'s datadir is always
+# `<prefix>/share`, so an arbitrary `$XDG_DATA_HOME` cannot be expressed as a prefix. The script
+# prints every path it wrote; the copy uses the install rule's file filter, so both destinations
+# carry the same tree.
+add_custom_target(install-help-user
+  COMMAND ${CMAKE_COMMAND}
+          -DHELP_SRC=${UDPSCOPE_HELP_SRC}
+          -DHELP_NAME=${UDPSCOPE_HELP_NAME}
+          -P ${CMAKE_CURRENT_SOURCE_DIR}/cmake/install_help_user.cmake
+  COMMENT "Installing the manual into the user's XDG data directory"
   VERBATIM)
 
 # --- UI files: GtkBuilder XML in a GResource ----------------------------------
@@ -97,8 +150,9 @@ add_custom_command(
   VERBATIM)
 # The generated source carries each file as one C string literal, and a `.ui` is big enough to pass the
 # 4095-character minimum the standard requires a compiler to support: `-Woverlength-strings` fires on
-# generated *data*, not on anything anyone wrote. Silenced for this one generated file (the icon and
-# help bundles are small enough per file never to need it), so the build stays at its four warnings.
+# generated *data*, not on anything anyone wrote. Silenced for this one generated file (the icon bundle
+# is small enough per file never to need it), so the build stays at its one warning. The manual is
+# no longer compiled in, so the help bundle's own warning is gone with it.
 set_source_files_properties(${CMAKE_CURRENT_BINARY_DIR}/udpscope_ui_resources.c
                             PROPERTIES COMPILE_OPTIONS "-Wno-overlength-strings")
 
@@ -127,6 +181,28 @@ else()
   message(WARNING "python3 was not found: the test-ui target is not available")
 endif()
 
+# --- the manual: an opt-in check, never part of `cmake --build` -----------------
+# The manual is hand-written Mallard, and `cmake --build` never reads it -- a broken xref or a
+# missing figure is a page in the viewer with no content or no image, not a build failure.
+# `tools/check_help.sh` runs yelp-check's four offline subcommands over the set (links, media,
+# orphans, ids) and renders the whole set to HTML with yelp-build, so the manual is checked the
+# way the `.ui` files are. `yelp-check validate` is *not* used: it fetches the Mallard RelaxNG
+# schema over the network, which is not available here and would make the check depend on it.
+#
+# No ALL: this runs only when it is named, so `cmake --build build` is unaffected and
+# yelp-tools is not a build dependency.
+find_program(UDPSCOPE_YELP_CHECK NAMES yelp-check)
+find_program(UDPSCOPE_YELP_BUILD NAMES yelp-build)
+if(UDPSCOPE_YELP_CHECK AND UDPSCOPE_YELP_BUILD)
+  add_custom_target(test-help
+    COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/tools/check_help.sh ${UDPSCOPE_HELP_SRC}
+    DEPENDS ${UDPSCOPE_HELP_FILES} ${CMAKE_CURRENT_SOURCE_DIR}/tools/check_help.sh
+    COMMENT "Checking the Mallard help set with yelp-check and yelp-build"
+    VERBATIM)
+else()
+  message(WARNING "yelp-check/yelp-build were not found: the test-help target is not available")
+endif()
+
 # --- build info: version, commit and timestamp compiled into the binary -------
 # Written at configure time so add_executable can name the file, and again on every
 # build so the commit and the timestamp belong to the binary that is running rather
@@ -148,7 +224,6 @@ set_source_files_properties(${UDPSCOPE_BUILD_INFO} PROPERTIES GENERATED TRUE)
 # --- the application ----------------------------------------------------------
 add_executable(udpscope
   ${CMAKE_CURRENT_BINARY_DIR}/udpscope_resources.c
-  ${CMAKE_CURRENT_BINARY_DIR}/udpscope_help_resources.c
   ${CMAKE_CURRENT_BINARY_DIR}/udpscope_ui_resources.c
   ${UDPSCOPE_BUILD_INFO}
   src/main.cpp
@@ -161,6 +236,20 @@ add_executable(udpscope
   src/waveform.cpp
   src/event_store.cpp
   src/acquisition.cpp
+  src/source/source_config.cpp
+  src/source/data_source.cpp
+  src/source/registry.cpp
+  src/source/udps_source.cpp
+  src/source/udps_kind.cpp
+  src/source/probe_source.cpp
+  src/source/e1608/e1608_link.cpp
+  src/source/e1608/e1608_device.cpp
+  src/source/e1608/e1608_source.cpp
+  src/source/e1608/e1608_kind.cpp
+  src/source/e1608/e1608_panels.cpp
+  src/source/flatudp/flatudp_signals.cpp
+  src/source/flatudp/flatudp_source.cpp
+  src/source/flatudp/flatudp_kind.cpp
   src/plot_host.cpp
   src/export.cpp
   src/search.cpp
@@ -180,13 +269,26 @@ add_executable(udpscope
   src/ui_status.cpp
   src/ui_measure.cpp
   src/ui_cursors.cpp
+  src/ui_dock.cpp
   src/ui_math.cpp
   src/ui_layout.cpp
+  src/ui_source.cpp
+  src/ui_slideover.cpp
+  src/ui_badges.cpp
   src/ui_trigger.cpp
   src/ui_signals.cpp
+  src/ui_signal_page.cpp
+  src/ui_context_help.cpp
+  src/ui_tour.cpp
 )
 
 target_include_directories(udpscope PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/src)
+# The manual's identifier (`show_help()` builds `help:<id>` from it) and its directory in the
+# source tree (what `help_self_check()` scans). Both come from the block near the top, so the
+# identifier is the desktop file's basename and nothing is written out twice.
+target_compile_definitions(udpscope PRIVATE
+  UDPSCOPE_HELP_NAME="${UDPSCOPE_HELP_NAME}"
+  UDPSCOPE_HELP_DIR="${UDPSCOPE_HELP_SRC}")
 target_link_libraries(udpscope PRIVATE plot::gtk4 udpsclient Threads::Threads
                                       PkgConfig::ADWAITA)
 add_dependencies(udpscope udpscope_build_info)

SPECS.md

@@ -42,9 +42,18 @@
 The following were built differently from what was asked for, each for a reason `README.md` states
 in full:
 
-- **`todo.md` item 2 — relative timing.** Implemented as `--relative-time`. The retained history
-  in this mode is **41.943 s** against the default **83.886 s** (measured at 100 kS/s, 4 channels,
-  `--buffer-mb 200`): exactly half, because a second f64 ring for absolute time raises a tick's
+- **The buffer is budgeted in samples per signal, not megabytes** (line 1 asked for "default 200MB
+  each, configurable as cli argument"). `--buffer-samples N` (default 10M, k/M/G suffixes) is the
+  number of samples kept for every acquired signal and for the shared time ring, rounded **down** to a
+  power of two ("up to"; 10M gives 8 388 608), and a separate application setting, `--memory-limit-mb`
+  (default 8192, also in Preferences), is the hard ceiling on the ring bytes, halving the sample budget
+  when the rings would not fit. The retained history therefore no longer depends on the channel count
+  or on relative time. There is no `--buffer-mb` and no compatibility shim; a stored `buffer_mb` is
+  ignored. The "2 identical buffers" were already a single ring plus latched snapshots (see below).
+- **`todo.md` item 2 — relative timing.** Implemented as `--relative-time`. *As first built* (under
+  the old byte budget; superseded by the item above, where both modes keep the same span and only
+  the memory differs) the retained history in this mode was **41.943 s** against the default
+  **83.886 s** (measured at 100 kS/s, 4 channels, `--buffer-mb 200`): exactly half, because a second f64 ring for absolute time raises a tick's
   cost from 24 to 32 bytes — a third more — and `Partition::time_capacity` is floored to a power
   of two, so a third more weight costs a full halving. The design document and the implementation
   plan both put the cost at ~22%, which is wrong; the per-byte figure of 75% is wrong for the same

cmake/install_help_user.cmake

@@ -0,0 +1,44 @@
+# SPDX-License-Identifier: MIT
+#
+# The `install-help-user` target's body. Copies the Mallard help set into the user's XDG data
+# directory -- where `help:<id>` resolves without root -- and prints every path it wrote.
+#
+# `$XDG_DATA_HOME` is honoured when it is set, and `$HOME/.local/share` is the fallback when it
+# is not: that is the XDG Base Directory Specification's own stated default for the variable, and
+# it is the default `help_installed_path()` falls back to as well, so the manual lands where the
+# application and the desktop viewer look for it. The variable names a *data directory*, not a
+# prefix -- its `share/` is not appended -- so the set goes to `<data_home>/help/C/<id>/`. An
+# arbitrary `$XDG_DATA_HOME` need not end in `share`, which is exactly why this copies the tree
+# rather than deferring to `cmake --install --prefix`, whose datadir is always `<prefix>/share`.
+#
+# Like the desktop-entry target, this runs only when it is named: `cmake --build build` never
+# touches the user's data directory.
+#
+# Expects -DHELP_SRC= and -DHELP_NAME= on the command line.
+
+if(DEFINED ENV{XDG_DATA_HOME} AND NOT "$ENV{XDG_DATA_HOME}" STREQUAL "")
+  set(data_home "$ENV{XDG_DATA_HOME}")
+elseif(DEFINED ENV{HOME} AND NOT "$ENV{HOME}" STREQUAL "")
+  set(data_home "$ENV{HOME}/.local/share")
+else()
+  message(FATAL_ERROR
+    "XDG_DATA_HOME and HOME are both unset or empty; cannot determine the user data directory")
+endif()
+
+if(NOT DEFINED HELP_SRC OR NOT DEFINED HELP_NAME)
+  message(FATAL_ERROR "HELP_SRC and HELP_NAME are both required")
+endif()
+
+set(dest "${data_home}/help/C/${HELP_NAME}")
+
+# The same filter as the install() rule, so both destinations carry the same tree: the pages and
+# the figures, and nothing an editor left behind.
+file(COPY "${HELP_SRC}/" DESTINATION "${dest}"
+     FILES_MATCHING PATTERN "*.page" PATTERN "*.png" PATTERN "*.jpg")
+
+# Printed because there is no uninstall target: undoing this is these paths.
+file(GLOB_RECURSE installed LIST_DIRECTORIES FALSE RELATIVE "${dest}" "${dest}/*")
+list(SORT installed)
+foreach(path IN LISTS installed)
+  message(STATUS "wrote ${dest}/${path}")
+endforeach()

docs/USER-GUIDE.md

@@ -6,9 +6,23 @@ what was built and why, and `SPECS.md` is the requirement document.
 
 ![the main window](img/main-window.png)
 
-*The main window with a source streaming: the signal panel on the right, the plot in the middle, the
-status line directly under it, and the toolbar above. The window control — `2 s` — is the first thing
-on the left.*
+*The main window with a source streaming: the header bar above (the window control — `2 s` — first on
+the left), the plot, the badge bar under it with one badge per signal, the status line at the foot, and
+the dock on the right with the cursor and measurement readouts and the events block.*
+
+The window is a plot with three things around it:
+
+- the **badge bar** under the plot: a badge for each signal you have switched on, a `+` to add one
+  (past six they fold into one `N signals` badge), and, on the right, **Trigger** and — only for a
+  source with controls of its own — **Source**;
+- the **side panel**, which a badge opens over the plot's right edge, one page at a time: the trigger,
+  a signal, the list of signals to add, the cursors, the measurements, the events, or a source's own
+  controls. A second click on the badge, `Esc`, **Close** or a click on the plot closes it, and it
+  never resizes the plot;
+- the **dock** on the right, which the dock button in the header bar (`s`) shows and hides: read-only
+  **Readouts** of the cursors and of the measurements, each with an **Edit** button that opens its
+  page, and an **Events** block. With the dock hidden, or in a narrow window where the dock slides over the plot, the readouts show in a
+  one-line strip under the plot instead (the cursors' deltas and each measurement's value; **Cursors** and **Measures** open the pages); the strip is there only while the cursors are on or there is a measurement.
 
 ## 1. Connecting
 
@@ -30,7 +44,7 @@ Every launch is its own process, so running two scopes side by side is fine.
 
 ## 2. The status line
 
-Directly under the plot, it reads `● <state> · <rate> · <window>`, and the ⓘ beside it opens the
+At the foot of the window, under the badge bar, it reads `● <state> · <rate> · <window>`, and the ⓘ beside it opens the
 detail: packets, frames, gaps, per-channel sample counts, the buffer's span and its decimation.
 
 - **The state word is one word** from a fixed set: `live`, `paused`, `armed`, `capturing`,
@@ -44,14 +58,43 @@ detail: packets, frames, gaps, per-channel sample counts, the buffer's span and
 
 ## 3. Signals
 
-The signal panel lists every signal the CONFIG described, with a switch each. **Signals start
-disabled — enabling one is what starts acquiring it**, and a signal nobody enables costs nothing.
-Drag a signal from the panel onto a plot row to add a trace; drag it again to another row to plot the
-same signal twice. The colour is per *signal*, so the same signal is the same colour wherever it
-appears.
+The **`+` badge** (or `g`) opens the **Signals** page, which lists what can be added: the signals the
+CONFIG described that are not acquired yet, each with a tick. **Signals start disabled — ticking one
+is what starts acquiring it**, and a signal nobody enables costs nothing. Its badge then appears in
+the badge bar. Drag the badge onto a plot row to add a trace; drag it again to another row to plot
+the same signal twice, or onto another badge to reorder the badges. The colour is per *signal*, so
+the same signal is the same colour wherever it appears.
 
-The panel also holds the per-signal calibration: gain and offset, applied at ingest, so the
-measurements and the export carry the same numbers the plot shows.
+Clicking a signal's badge opens its own page. Directly under the name are its **Unit**, **Gain** and
+**Offset** — each with a pencil button that edits that one value — and then what the stream declared about
+it (type, size, range, sample rate, timing). Below come the colour and the **Plot on** buttons for the
+rows. Gain and offset are applied at ingest, so the measurements and the export carry the same numbers the
+plot shows; a renamed unit is used there too and is saved with the session.
+
+### Splitting a row
+
+Press `l` (or pick **Layout editor** from the overflow menu) to arrange the plots: a **`×`** at the top
+left of each plot removes it, a **`+`** on each boundary between rows adds a row, and a **Done** button
+in the plot's top-right corner leaves the editor. The plots can also be put **side by side**: a row holds
+up to **4** plots, and the figure up to **8** in all.
+
+- **To split a row**, click the `+` at its left or right edge, or the `+` between two of its plots. The
+  new plot is empty and the plots after it keep their traces. The `+` is dim at 4 plots in the row or 8
+  in the figure.
+- **To resize**, drag the double-headed arrow between two plots left or right. The two neighbours trade width (each
+  stays at least about 96 px wide); the sizes are saved with the session.
+- **To remove a plot**, click its `×`. In a split row it removes just that plot and its traces; in a row
+  of one plot it removes the row.
+
+Every plot shares **one time window**: panning or zooming in any of them moves them all, the crosshair
+sits at the same time in each, and the vertical cursors are the same two times in each. The plots of a split
+row also share **one y range**: the y labels are drawn at the left of the first plot only, the
+horizontal rulers are the same two values in every plot, and a y zoom, pan, fit or fixed range in any of
+them applies to the whole row. The time labels sit under the bottom row, and
+under any row above it whose columns differ from the row below. A plot of a split row is named by its row and a letter, `2a` to `2d`: that is what the signals
+page's **Plot on** buttons and the status line call it, and a signal dragged
+from its badge goes onto the plot under the pointer. The arrangement is saved per source, and a session
+saved before rows could be split opens with one plot per row, as it was.
 
 ## 4. The window and navigation
 
@@ -83,8 +126,9 @@ should look like.
 *Single mode with a capture held: the axis is the event's own `[-pre, +post]`, the trigger marker
 sits at the edge, and the status line reads `event held`.*
 
-The trigger panel has the edge, the pre/post split (as a share of the event span), Normal or Single,
-and Arm/Disarm. Selecting a signal for the trigger enables it.
+The trigger button in the header bar (`t`) turns trigger mode on. The **Trigger** badge opens the
+trigger page, which has the signal, the condition, the edge, the pre/post split (as a share of the
+event span), Normal or Single, and Arm/Disarm. Selecting a signal for the trigger enables it.
 
 - **While a capture fills** the plot keeps drawing live data on the event's clock, so the post side
   fills in view; the axis does not move.
@@ -94,6 +138,10 @@ and Arm/Disarm. Selecting a signal for the trigger enables it.
   when you disarm is the picture you keep.
 - The event window is counted in **stream seconds** end to end, so a source whose clock advances in
   jumps still gets the window it asked for.
+- **Events.** With *record events* on (trigger page), each latch is stored. The dock's **Events** block
+  lists them newest first and **one click replays** one; **Manage** opens the full list as a page,
+  where a click selects, a double click replays, and **Compare**, **Accumulate** and **Live** act on
+  the selection or go back to the stream. The block is dimmed until something is recorded.
 
 ## 6. Pause
 
@@ -104,22 +152,24 @@ does not walk it off its snapshot.
 
 ## 7. Cursors
 
-The cursors toolbar toggle switches on two instruments per row:
+The cursors toggle in the header bar (`c`) switches on two instruments per row:
 
-- **vertical** — two times, shared by every row;
-- **horizontal** — two rulers per row;
+- **vertical** — two times, shared by every row (and every plot of a split row);
+- **horizontal** — two rulers per row (every plot of a split row shows the same two values);
 - **both** — the two together;
 - **mix** — the two times, read off each *trace* where they cross it.
 
-The pane beside it reports each trace's values at the markers, and **Reset** puts them back at the
-window's edges. Values read `--` when a marker is past the newest sample and `partial` when only one
+The dock reports each trace's values at the markers; **Edit** beside **Cursors** opens the page with
+the mode and **Reset**, which puts them back at the window's edges. Values read `--` when a marker is past the newest sample and `partial` when only one
 marker is over data.
 
 ## 8. Measurements
 
-The measurements pane computes statistics of the **visible window** of a signal: average, top,
-bottom, min, max, peak to peak, amplitude, pulse duration, period and frequency. `+` adds one, the
-row's pencil edits it, and **show on plot** draws its result as a ruler (levels) or markers (times).
+A measurement is a statistic of the **visible window** of a signal: average, top, bottom, min, max,
+peak to peak, amplitude, pulse duration, period and frequency. `m`, or **Edit** beside
+**Measurements** in the dock, opens the page; its `+` adds one, a click on a row (in the page or in
+the dock) edits it, and **show on plot** draws its result as a ruler (levels) or markers (times).
+The dock shows each measurement's value.
 
 `top` and `bottom` take a *split* as a share of the window's own range — the percentage travels
 between signals where a threshold in volts would not. `period` and `frequency` deliberately have no
@@ -127,7 +177,7 @@ split: they count rising crossings of the mid level, one edge per cycle, and a s
 setting you can only get wrong.
 
 The values are refreshed on a cadence — at most every 100 ms while the window is scrolling, once when
-it stops, and once per mode change — so a live view cannot cost you frames. The pane's cost is
+it stops, and once per mode change — so a live view cannot cost you frames. The cost is
 reported in the exit dump with the app's self-check.
 
 ## 9. Math channels
@@ -139,13 +189,14 @@ the square on the right. The orange dot marks the node that carries the channel'
 
 A math channel is derived from the others and is then an ordinary channel: enable it and it is
 acquired, plotted, measured and exported like a streamed signal, and another math channel can use it
-as a source.
+as a source. The **Signals** page lists them under a `MATH` heading whose `+` creates one; a math
+channel's own page has **Edit graph** and **Delete**.
 
 Operations: `channel` (a source), `gain + offset`, `abs`, `sqrt`, `clamp`, `low pass`, `high pass`,
 `band pass` (biquads, corner in Hz against the stored rate), `sum`, `difference`, `product`, `ratio`.
 
 - **Click** a node to select it; its parameters appear in the form beside the canvas.
-- **Click an output square, then an input square**, to wire them. An input is only offered the nodes
+- **Drag from an output square to an input square** to wire them. An input is only offered the nodes
   above it — the graph is a list walked in order, so a cycle cannot be drawn.
 - **Drag** a box to move it. **add node**, **delete node** and **set as output** are below the form.
 - The **output is the last node** of a graph you build top to bottom, and the orange dot says which;
@@ -180,19 +231,24 @@ per sample, `time`, `stream_time`, then one column per signal.
 |---|---|
 | `space` | pause / resume |
 | `a` | arm / disarm the trigger |
-| `t` | the trigger panel |
-| `l` | the layout editor |
-| `g` | go live |
-| `f` | fit to data |
-| `d` | add the first free signal to the focused row |
-| `c` | cursors on/off |
-| `m` | measurements pane |
-| `e` | export |
-| `?` | shortcuts |
+| `t` | enable / disable trigger mode |
+| `c` | enable / disable the cursors |
+| `m` | open or close the Measurements page |
+| `g` | open or close the Signals page (the `+` badge opens it too) |
+| `l` | show / hide the layout editor |
+| `s` | show / hide the dock |
+| `Esc` | close the slide-over page (the guided tour takes it first) |
+| `f` | fit to data (the plot's own key) |
+| `Ctrl+E` | export visible range |
+| `F1` | open the manual |
+| `Ctrl+/` | open the shortcut overview |
+| `Ctrl+T` | start the guided tour |
+| `Ctrl+H` | turn the contextual help on or off |
+| `Ctrl+Q` | quit |
 
-`Ctrl+E` exports, `Ctrl+Q` quits, `Ctrl+plus`/`Ctrl+minus` zoom x and `Alt+plus`/`Alt+minus` zoom y.
-A keystroke is ignored while a text field has focus, so typing in the window control never arms the
-trigger.
+The plot also answers `+`/`-` (zoom both axes), `Ctrl+plus`/`Ctrl+minus` (zoom x only),
+`Alt+plus`/`Alt+minus` (zoom y only) and the arrow keys (pan). A keystroke is ignored while a text
+field has focus, so typing in the window control never arms the trigger.
 
 ## 13. Troubleshooting
 

docs/claude/architecture.md

@@ -10,8 +10,8 @@ concluding something is a bug.
 
 ### Threads
 
-Exactly two: a producer thread in `Acquisition` owns `udps_client_t` and calls
-`udps_client_poll()`; the GTK main thread owns every widget and GL context. They share
+Exactly two: a producer thread in `Acquisition` owns a `DataSource` and calls
+`source->poll(50)`; the GTK main thread owns every widget and GL context. They share
 `ScopeModel` under `ScopeModel::mutex()`, taken once per DATA frame by the producer and
 once per frame by the UI (`tick()` in `src/ui.cpp`) around `RowSet::bind()`/`acquire()`.
 Samples themselves cross via `plot::data::RingBuffer` (single producer, single
@@ -21,11 +21,169 @@ consumer) and never through the lock. Cross-thread scalars are atomics on `Scope
 before `trigger_pending_` and those two carry release/acquire, so a consumer that sees a
 capture open sees which edge it belongs to.
 
+### Sources
+
+What feeds `Acquisition` is a `DataSource`, one of the registered *kinds*.
+
+- The kinds live in `src/source/`. `register_builtin_sources()` fills the registry explicitly --
+  there is no static-initialiser registration, which a linker may drop -- and a future `dlopen`
+  loader would only call `register_kind()`.
+- A `DataSource` delivers into `Acquisition` (a `SourceSink`) from inside `poll()`. `Frame` is
+  source-neutral, and its pointers are valid **only during `on_data`**: copy what is kept.
+- The GTK thread reaches a source **only** through `DataSource::post(Command)`; the queue is drained
+  at the top of `poll()`. A panel never calls a source directly.
+- `UdpsSource` wraps `deps/udpsclient` unchanged; `udps_*` names appear only in
+  `src/source/udps_*.cpp` (`grep -rn "udps_" src` outside those files is a leak of the old coupling).
+- The frame is **single-timebase**. A multi-timebase source (ABScope) will change the interface and
+  the data path together; do not bend one frame to carry two clocks.
+- A kind's capability panels are pages of the slide-over (`slideover_add_page`), named `source-<id>`. A disconnected source
+  leaves them **insensitive, not hidden** (`apply_source_panels` in `src/ui_source.cpp`).
+- Session file naming for a non-UDPS kind: the pseudo-host is `<kind>-<identity>` (characters outside
+  `[A-Za-z0-9._-]` become `_`) on port **1** (0 is rejected by the session-file parser), the kind is
+  stored as `source_kind` and its settings as `source_opt_<key>`. A UDPS file keeps `<host>_<port>` and
+  has neither key, so a legacy session is read as UDPS and nothing existing moves.
+- **The E-1608 kind has three layers, and only the top one knows the framework.** `e1608_link`
+  (discovery, handshake, framed TCP commands, the scan socket) and `e1608_device` (typed commands,
+  factory calibration, `decode_scans`) are plain POSIX C++ with no GTK or `DataSource` types; discovery is
+  `Scan` (one socket per interface, polled by the caller: the form polls it from a GLib timer on the main
+  thread, the source's lookup goes through `discover_broadcast`);
+  `e1608_source` is the `DataSource`; `e1608_kind` and `e1608_panels` are the UI. A change to the wire
+  never reaches the UI files.
+- The E-1608 source runs **everything inside `poll()`** on the producer thread: posted commands, the
+  connect state machine (Down, Scanning, Halted), the scan read, the 500 ms status check (its not-running restart is skipped when a hardware trigger is configured), the digital
+  input/counter poll and the waveform tick (every `1 / gen_rate` s, 20 ms by default; one synchronous DAC write per running channel, so a slow board lowers the rate it achieves, which the Analog out panel reports). There is no second thread. A connect attempt (discovery,
+  handshake, calibration read, scan start) can block `poll()` for as long as the command timeout allows each
+  step; that delays only the command queue. Every exception is caught inside `poll()`: an escape would end
+  the producer thread, and `drain_commands()` runs inside the same `try` for that reason.
+- Its frames are **fixed-size blocks** of about 10 ms (`round(scan_rate / 100)` scans, 1 to 4096), not
+  whatever one `recv` returned: `build_stamps` warns once when a frame's sample count differs from the
+  first one's. Digital lines and the counter are held across a block (a step trace).
+- The E-1608 panels read the board's state from `E1608Readouts`, a set of atomics the producer writes
+  and a tick callback throttled to 100 ms reads; a panel never touches the source's internals, and writes
+  only through `post()`. `Acquisition::on_event` ignores the detail string and does nothing for `Error`,
+  so the source also writes each new error to stderr as `[e1608] ...` (once per distinct message, not per
+  retry); that line is where a user sees why a connection failed.
+- **The flat UDP kind is three files and no thread.** `flatudp_signals` is the `signals` string codec,
+  the validity rules and the decoders, with no GTK and no sockets (the probe round-trips it);
+  `flatudp_source` is `FlatUdpSettings` plus the `DataSource`; `flatudp_kind` is the form, a signal-row
+  editor (a name, a type, a count and, while the count is above 1, a "Vector as" drop-down per row). The
+  datagram has no description, so a list that is wrong is invisible except as dropped datagrams: the size
+  check is the only defence, and it is why a wrong-size datagram is counted (`stale`) and reported once per
+  size.
+- A vector row is shown one of two ways, chosen per row (`Row::wave`, the `w` suffix in the text). As
+  **channels** it is `count` scalar channels of one sample per cycle, so the list batches like an
+  all-scalar one. As a **waveform** it is one channel with `rows = count` and
+  `sampling_rate = rate * count`, one datagram per `Frame` (`num_samples = 1`). The two cannot share a
+  list because the model spans a frame by its largest element block and `Frame::value` is 0 past a scalar's
+  one value: a scalar beside a vector block would be zero-padded, so `problem()` demands that a list with a
+  waveform row be waveform rows of one count, and the form shows that message in the subtitle. The channel
+  total is capped at 256.
+- Its frames are **fixed-size blocks** like the E-1608's for the same reason (`build_stamps` warns when the
+  sample count varies): `round(rate / 100)` datagrams for a list with no waveform row, a partial block
+  flushed after 100 ms. `rate` is required because `sampling_rate = 0` makes the model size the ring and
+  the ingest decimation for 1 kHz; there is no time-base switch, since `acquisition.cpp` has no stamping
+  path that ignores the declared cadence.
+- `Disconnected` after 2 s without a *valid* datagram (wrong-size ones do not refresh the clock); it resets
+  `Acquisition`'s per-session state, so the next datagram re-anchors rather than reading as a gap, and the
+  history survives (`CONFIG` is sent once, from the first `poll()`).
+- The form's row editor removes a row from inside its own button's `clicked` emission (GTK keeps the emitter
+  alive to the end of the emission, and the handler copies the form and the row out of its context first);
+  every handler tests `Form::alive`, which the groups' `destroy` clears, because the chooser may have
+  destroyed the sibling widgets the handlers reach by raw pointer.
+
+### The window's chrome: plot, slide-over, badge bar, dock
+
+The main window is a plot with three things around it, each a unit of `src/ui_*.cpp` and none of them
+touching the data path.
+
+- **`SlideOver`** (`src/ui_slideover.cpp`) is one `GtkRevealer` holding a `GtkStack`, added as the second
+  child placed *over* the plot (after the layout editor's buttons) in `GtkOverlay#plot_overlay`. A page is
+  a `slideover_add_page(app, id, title, widget)`: the widget is wrapped in a `GtkScrolledWindow` of its
+  own and registered under its id (`trigger`, `source-<id>`, `signals` (the signal list) and
+  `signal:<name>` (one signal's page, `src/ui_signal_page.cpp`, created on demand by `signal_page_ensure()`
+  and pruned by `signal_pages_sync()`, which `rebuild_signal_panels()` ends with), `cursors` (the cursors
+  panel, unchanged) and `measure` (the measurements panel, unchanged; `m` toggles it); `events` (the full events list, `events-pane.ui`'s `events_box`: the Live, Compare and Accumulate
+  controls and the multi-select list with its thumbnails; open it only through `open_events_page()`, which
+  refreshes the list first, because the slide-over has no on-open hook). They are registered whether or not
+  they are open (a closed page's widgets exist, unmapped); `cursors` and `measure` are insensitive until the
+  stream has signals, by the same `update_signal_availability()` call that sets the dock's sensitivity, and
+  `events` follows `sync_events_availability()` (below). One page is open at a time and `App::slideover.page`
+  is its id, empty when closed. The open page is **not** a session value. Esc, *Close*, a second click on the
+  badge and a click on the plot close it; the click-away is a capture-phase observer (see
+  [invariants-gtk-and-chrome.md](invariants-gtk-and-chrome.md)). With two or more `source-*` pages, an
+  `AdwToggleGroup` under the header is the segmented switch between them.
+- **`BadgeBar`** (`src/ui_badges.cpp`) is the fixed-height row between the plot and the status line
+  (`main-window.ui` `badge_bar`, two slots: signals, left, a scroller holding one badge per enabled signal
+  and the `+`, or a single "N signals" badge past six; system, right, holding the **Trigger** and
+  **Source** badges). `sync_signal_badges()` rebuilds the signal badges (from `rebuild_signal_panels()`);
+  their order is `App::badge_order`, in memory only. A badge is a flat button whose `page` is the slide-over page it
+  toggles; the Source badge's page is the first `source-*` page, and a kind with none (UDPS, Flat UDP, a
+  file) leaves it **hidden** (the user asked for hide here, not the usual disable): `sync_badge_bar()` sets its visibility,
+  pick and focus from `slideover.source_pages` being non-empty every tick, so anything that indexes the badge
+  (the tour's `badges` step targets the whole bar, `[badges]`) must tolerate it being absent.
+- **The dock** is the `AdwOverlaySplitView` sidebar (`side_box` > `dock_scroller` > `dock_page`), **280 px**
+  and fixed. It holds two things, the **Readouts** box and, under a separator, the **Events** block (below). The Readouts box (`src/ui_dock.cpp`, `build_readouts_dock()`): a
+  **Cursors** block (heading, an **Edit** button that opens the `cursors` page, a `GtkGrid` of a header row
+  `A B delta` and one line per page line) and a **Measurements** block (heading, **Edit** opening the
+  `measure` page, one line per measurement: chip, type, value; a click on a line opens that measurement's
+  dialog; no measurements shows one dim "no measurements" line). It is read-only and **owns no formatting**:
+  `update_cursors_pane()` and `update_measures()` hand the string they wrote to the page's label to
+  `dock_cursor_cell()` / `dock_measure_value()` as well, and `rebuild_cursors_pane()` /
+  `rebuild_measures_pane()` end by rebuilding the dock's lines to match (`dock_rebuild_cursors()`,
+  `dock_rebuild_measures()`). It holds no tab switcher, no revealer and none of the full panels, nor a source
+  kind's panels (those are slide-over pages). The window's measurement editor is a dialog
+  (`open_measure_dialog()`), not part of the `measure` page.
+
+  **The readouts strip** (`readouts_strip` in `main-window.ui`, between `plot_overlay` and `badge_bar` in
+  `left_column`; filled by `ui_dock.cpp`) carries the same readouts when the dock is not beside the plot: a flat
+  **Cursors** button and one chip (`who` + delta) per cursor line, then a **Measures** button and one chip per
+  measurement. `sync_readouts_strip()` shows it exactly when `(!adw_overlay_split_view_get_show_sidebar() ||
+  adw_overlay_split_view_get_collapsed())` **and** (the cursors toggle is active **or** `app.measures` is
+  non-empty) -- the Dock button put the dock away, or the window is collapsed and the dock is an overlay on the
+  plot (the strip stays on screen even while that overlay is open), and there is something to read. Inside, the
+  Cursors group (`strip_cursor_group`) is shown with the cursors on, the Measures group (`strip_measure_group`)
+  with measurements, the separator (`strip_sep`) with both; with neither the strip is hidden. Besides the tick,
+  the cursors toggle handler and `rebuild_measures_pane()` call it, so a toggle or an add/delete shows at once. The tick
+  calls it right after re-asserting `sidebar_wanted` and *before* `set_collapsed()` (so the split view's own
+  collapse-time `show-sidebar` write is never read); that means the `collapsed` it reads is the previous
+  frame's, and the strip follows a collapse or a widening one tick late, never through a wrong state. Its labels (`strip_cursor_who`, `strip_cursor_deltas`, `strip_measure_labels`) are rebuilt by
+  `dock_rebuild_cursors()` / `dock_rebuild_measures()` and written by `dock_cursor_cell()` /
+  `dock_measure_value()` from the same argument as the dock's, so there is no second formatter;
+  `dock_set_cursors_sensitive()` is the one writer of the cursor readouts' sensitivity (the dock's grid and
+  the strip's chip box).
+
+  The **Events** block (`build_events_dock()`, also `ui_dock.cpp`) is a heading with a **Manage** button
+  (`open_events_page()`) over a short list (`dock_events_list`, 112 px, scrolled, no thumbnails): one compact
+  row per `EventRecord`, newest first, capped at `kDockEventsMax` (24) with a dim "... N more, see Manage"
+  row after them. A row's cells are a one-character marker (filled = the event on screen; hollow = a member
+  of the group on screen -- dock only, the page's rows do not mark members; blank otherwise), the title
+  (`event_row_title`, ellipsized, full text in the tooltip) and `#<seq>`; **one click replays** it
+  (`replay_event()`, the body of the page's double-click handler). Both views are rebuilt from one
+  `EventStore::list()` by `refresh_events_pane()`, but on different cadences: **the dock follows every
+  latch** (`record_event()` refreshes it unconditionally), while the page's list is refreshed per latch only
+  while the page is open and by `open_events_page()` otherwise. `mark_events_on_screen()` updates titles and
+  markers in place and never rebuilds either list. The block, and the page, are insensitive (never hidden)
+  unless `sync_events_availability()` says `event_recording || replaying || events_cached` -- a different
+  rule from the spec's (see [invariants-trigger-and-pinning.md](invariants-trigger-and-pinning.md)).
+  There is no events pane, divider or header toggle any more: the page is reached from Manage (or by a
+  caller of `open_events_page()`), and the plot is never squeezed by events.
+
+**When each is built and when it is read.** `build_slideover()` runs in `on_activate` right after the tour
+overlay is built (the tour's overlay wraps the whole window, so its dim rectangles cover the slide-over
+too); the trigger form is registered as
+a page by `build_trigger_panel`; `build_source_panels()` registers the source pages; and
+`build_badge_bar()` runs *after* all of them, because the Source badge needs to know the first page.
+Per-tick state (the Trigger word, the Source name, the open marks) is written by
+`sync_badge_bar()`, called from `tick()` and from `slideover_open`/`slideover_close`; it writes a label
+only when its text changed. Nothing in the badge bar or the slide-over may be read from the producer
+thread.
+
 ### Data path
 
 `ScopeModel` holds **one `BufferStore`** (`live()`): one shared time-base ring plus one
-value ring per channel, sized by `plan_partition()` to cover `--max-window` seconds
-within the byte budget. The producer always writes it, whatever the trigger is doing —
+value ring per channel, sized by `plan_partition()`: `--buffer-samples` ticks (rounded down to a power of two) per ring, halved
+until the real bytes fit `--memory-limit-mb` (`Partition::memory_limited` records a clip), and the shared
+clock decimated until `--max-window` seconds fit. The producer always writes it, whatever the trigger is doing —
 that is what guarantees a full pre-trigger history on the *first* latch after arming.
 The spec's second buffer (item 1) is the latched `EventSnapshot`, which is already an
 immutable copy of the captured window; see README for why two live rings were dropped.
@@ -101,12 +259,15 @@ Layers to keep straight:
   `ChannelBuffer` is a `plot::data::Series` over a (value, time) ring pair.
 - `SlotSeries` (`src/channel.hpp`) — a trace's stable series object, rebound each frame
   to either a `ChannelBuffer` or an `EventSeries`.
-- `RowSet` (`src/plot_host.hpp`) — **one `plot::Figure`** of up to `kMaxRows` rows (added
-  and removed one at a time by the layout editor), each a
-  borrowed `plot::Plot*` with `kSlotsPerRow` fixed trace slots. The figure owns
-  everything the rows have to agree on: the x window (one x link group every row joins),
+- `RowSet` (`src/plot_host.hpp`) — **one `plot::Figure`** of up to `kMaxRows` **plots** (rows are added
+  and removed one at a time by the layout editor, and a row can be split into up to
+  `kMaxCellsPerRow` cells side by side), each plot a
+  borrowed `plot::Plot*` with `kSlotsPerRow` fixed trace slots; `row(i)` indexes the plots row-major,
+  `figure_row_count()` counts the rows. The figure owns
+  everything the plots have to agree on: the x window (one x link group every plot joins),
   the live follow (the *group's* — a member's own axis must be `XFollow::Off`, since
-  `Figure::link_x()` refuses a `Live` member), the left gutter and the crosshair.
+  `Figure::link_x()` refuses a `Live` member), the y range of each figure row's cells (`set_share_row_y`: a split
+  row has one y axis, one ruler pair and one fit), the left gutter and the crosshair.
 
 - `ExportTable` (`src/export.hpp`) — the visible window as columns, collected from the
   snapshot or the live rings and handed to the `.npy`/`.csv` writers. Always the stored

docs/claude/build-and-run.md

@@ -13,8 +13,11 @@ cmake --build build
 
 ./build/udpscope --server 127.0.0.1 --port 8000
 ./build/udpscope --server 10.0.0.5 --port 8000 --multicast 239.1.2.3 --interface 10.0.0.9
+./build/udpscope --source udps --source-opt server=127.0.0.1 --source-opt port=8000   # same as --server/--port
 ```
 
+`--help` lists the registered source kinds.
+
 The app can be launched from the shell rather than only from a terminal, but only on request:
 
 ```sh
@@ -52,16 +55,130 @@ here is needed to *build* the application. `blueprint-compiler` and `python3` ar
 time; without them the target is absent rather than silently passing. `tools/check_ui.py --lint` also
 prints the linter's advice, which is advice and deliberately not a gate.
 
-Options: `--server`, `--port`, `--multicast`, `--interface`, `--buffer-mb` (per
-buffer, default 200), `--max-window`, `--holdoff`, `--recv-buffer`, `--plots` (the row
+The manual has its own check, the same shape:
+
+```sh
+cmake --build build --target test-help
+```
+
+That runs `yelp-check`'s four offline subcommands over `help/C/<id>/` (links, media, orphans, ids)
+and renders the whole set with `yelp-build html` into a temp directory, so the manual is checked the
+way the `.ui` files are. **`yelp-check validate` is deliberately not used**: it fetches the Mallard
+RelaxNG schema over the network, which is absent on a build box, so it would fail for that reason and
+not for a fault in the pages. `yelp-check`/`yelp-build` are found at configure time; without them the
+target is absent rather than silently passing.
+
+The manual is a Mallard set under `help/C/<id>/`, installed by an `install()` rule to
+`<datadir>/help/C/<id>/` — where the freedesktop Help System Specification's `help:` URI resolves
+`help:<id>` — so it is *read from a datadir by another process* even though the binary itself has no
+install step. `F1` opens it in Yelp through that URI. The document identifier is the desktop file's
+basename (`data/org.udpscope.app.desktop.in` → `org.udpscope.app`), so it is the `.desktop` name, the
+GApplication id and the install directory at once. The figures are regenerated by
+`tools/make-help-shots.sh`, which drives the app headlessly against the mock and draws the annotation
+boxes with ImageMagick; Mallard is translatable with `itstool`, but only the `C` set is authored.
+
+Because the manual is the only thing udpscope installs, it can be installed *alone* — where `help:`
+finds it, and without the `cmake --install` of a whole project — by either of two opt-in targets.
+Neither is built by default and `cmake --build build` never touches either:
+
+```sh
+cmake --build build --target install-help-user   # <data-home>/help/C/<id>/, no root
+cmake --build build --target install-help         # <CMAKE_INSTALL_PREFIX>/share/help/C/<id>/
+```
+
+`install-help-user` writes to `$XDG_DATA_HOME` when it is set and to `$HOME/.local/share` when it is
+not — the XDG Base Directory Specification's own default for the variable, and the fallback
+`help_installed_path()` uses — so it needs no root and lands the set exactly
+where `F1` and the alert look for it. `install-help` goes through the install machinery into the
+configured `CMAKE_INSTALL_PREFIX`, so a packager or a system-wide user points it at `/usr` with
+`-DCMAKE_INSTALL_PREFIX` at configure time. Neither target can install system-wide by itself: a build
+target has no more privilege than the shell that ran it, so `install-help` writes to the configured
+prefix and a system-wide caller wraps it in `sudo`. Both print where they wrote. Both land the same
+tree the `install()` rule does — the user-local copy applies that rule's file filter, and the
+prefix-wide target *is* that rule, reached through the `Help` component
+(`cmake --install --component Help`) — and the ordinary `cmake --install` still installs every
+component, so its behaviour is unchanged.
+
+Options: `--source NAME` and the repeatable `--source-opt k=v` (the source kind and its settings;
+`--server`, `--port`, `--multicast` and `--interface` populate the UDPS entries of the same options),
+`--server`, `--port`, `--multicast`, `--interface`, `--buffer-samples` (samples
+per acquired signal, default 10M, k/M/G suffixes, rounded down to a power of two),
+`--memory-limit-mb` (hard ceiling on the ring bytes, default 8192; also a Preferences row),
+`--max-window`, `--holdoff`, `--recv-buffer`, `--plots` (the row
 count to *start* with, 1..`RowSet::kMaxRows`; the layout editor owns it afterwards),
 `--capture-packets N` (the raw-datagram ring of README's "Packet capture"; 1..100000,
 the value is required, and the popover button uses 1000 when the flag was absent).
 The flag is **not** persisted in the session file: persistence of the enable state
 belongs with `todo.md` item 3, alongside the relative-time toggle.
+`--renderer cairo|gl|vulkan` exports `GSK_RENDERER` **at the top of `main()`** —
+before `choose_source()`'s `adw_init()` and `run_ui()`'s, because GSK reads the variable when
+it creates its renderer and setting it later is a silent no-op. `cairo` is the software preset
+and also exports `LIBGL_ALWAYS_SOFTWARE=1`: the plot is a `GtkGLArea`, so a display with no
+usable GPU fails twice, and this is the pair `tools/make-help-shots.sh` already sets. Nothing
+is exported when the option is absent, so GTK's own choice stands.
+
+`--source e1608` selects the MCC E-1608 Ethernet DAQ; its settings are `--source-opt` keys, all optional
+(`address` or `mac`+`subnet`, `port` 54211, `code` 0, `timeout_ms` 2000, `scan_rate` 1000 per channel,
+`ext_clock`, `trigger` `none|rising|falling|high|low`, `auto_restart` 1, `calibrate` 1, `poll_rate` 10,
+`gen_rate` 50 (Hz, 1 to 200: the waveform generator's DAC update rate), `mode` `se|diff`, `ai0`..`ai7` `BIP10V|BIP5V|BIP2V|BIP1V` (an absent key = off, **and any `aiN` key at all
+drops the default**: only a run with no `aiN` key gets `ai0=BIP10V`, so `ai1=BIP5V` alone is channel 1
+alone, and a value that is not a range name is a channel that is off), `dir0`..`dir7` `i|o`,
+`plot0`..`plot7`, `plot_counter`, `do_init`, `ao0_init`, `ao1_init`). Either `address` or `mac` is
+required; a MAC with no `address` is looked up by a broadcast sent on every interface (`Scan`), or by a sweep of
+`subnet` (`a.b.c`).
+The enabled channels times `scan_rate` must not exceed 250 kS/s. `tools/mock_e1608.py` is a protocol
+mock of the board for development (UDP discovery and handshake, TCP commands, a scan stream with a sine
+per channel, calibration memory, `--port`, `--mac`, `--log FILE`, `--drop-after S` and `--overrun-after S`
+switches, `--code N`); the mock stands in for the board (a real board has been run once, with one channel; see
+the README), and the mock's header lists the items whose layout is unverified. Errors are written to stderr as `[e1608] ...`, once per distinct message.
+
+```sh
+python3 tools/mock_e1608.py --port 54711 &
+./build/udpscope --source e1608 --source-opt address=127.0.0.1 --source-opt port=54711 \
+  --source-opt ai0=BIP10V --source-opt ai1=BIP5V --source-opt plot0=1
+```
+
+`--source flatudp` receives the MARTe2 `UDPSender` datasource (one datagram per cycle: the signals
+concatenated in declaration order, no header, no padding). The datagram carries **no description**, so the
+settings are the whole contract: `port` 44488, `bind`, `multicast` and `iface` (a group to join and the local
+interface for it), `rate` (the sender's cycle rate in Hz; **required**, it sizes the ring and the ingest
+decimation and spaces the samples within a frame), `endian` `little|big`, and `signals`
+`name:type[count][w],...` with types `uint8/16/32/64`, `int8/16/32/64`, `float32`, `float64`, e.g.
+`Trigger:uint8,Ia:float32,Wave:float32[16]`. A count above 1 makes a vector signal, shown one of two ways: by
+default as `count` **channels** `Wave[0]`..`Wave[15]` of one sample per cycle each (batched like any scalar
+list); with a trailing `w` (`Wave:float32[16]w`) as ONE **waveform** channel receiving `count` consecutive
+samples per cycle at `rate * count`, as a UDPStreamer block signal. A waveform row needs a count above 1, a
+list with one holds only waveform rows of one count (no zero-padding of scalars), and a list may make at most
+256 channels (a scalar 1, a `channels` row `count`, a waveform 1). A datagram of any other size than
+the list implies is dropped and counted as stale; each distinct wrong size is reported once on stderr as
+`[flatudp] ...`. Loss is never reported: the stream has no counter. `tools/mock_flatudp.py` is a sender for
+a signal spec (`--rate`, `--signals`, `--big-endian`, `--gap S,D`, `--bad-every S`, `--multicast G --mcast-if A`,
+`--log FILE`).
+
+```sh
+python3 tools/mock_flatudp.py --port 44588 --rate 1000 --signals 'Trigger:uint8,Ia:float32,Wave:int16[4]' &
+./build/udpscope --source flatudp --source-opt port=44588 --source-opt rate=1000 \
+  --source-opt 'signals=Trigger:uint8,Ia:float32,Wave:int16[4]'
+```
+
+(Quote the `signals` value: zsh globs the `[4]`. The mock takes the same text with or without the trailing `w`;
+the datagram is the same, `w` only says how the app shows it.)
 
 `tools/mock_udpstreamer.py` has waveform-injection options used by the probes:
 
+- `--square-harmonics N` shapes `square`: `N` odd harmonics of the ideal step's Fourier
+  series, so each edge overshoots by the Gibbs constant (about 9 % of the 2 V swing at the
+  default 30, i.e. `y = ±1.179`) and then rings — a band-limited edge, which is what a
+  crossing count or a pulse-width test has to survive. The series is deterministic and the
+  odd harmonics keep the ideal wave's edge instants and its polarity, so the level-0 trigger,
+  the search and the glitch's inverted pulse still read where they did on the step; the
+  *extremes* are what move. `0` (or negative) is the ideal ±1 step, which is what a probe
+  asserting an exact extreme or an exact width asks for — the noise probe's group-delay leg is
+  the one that does, because its `want` is the analytic `tau*ln2` of a step
+  (see [verification.md](verification.md)). It costs the producer about 0.5 ms per
+  2000-sample packet on top of the ideal branch, so at the fast mock's 1.3 MS/s the mock
+  delivers at roughly nine tenths of its declared pace — a reading that scales with the
+  retained span reads that much lower, and nothing else does.
 - `--glitch-at S` / `--glitch-width W` invert the `square` signal for `W` seconds at the
   start of every square period from stream second `S` onwards — a runt pulse of a known
   width, which is what a `<` pulse-width trigger and a glitch search are checked against.
@@ -152,6 +269,66 @@ adapter `PlotArea`'s **figure mode** —
 `set_figure()`, one `input::Controller` per row, nearest-row event routing, a
 figure-wide crosshair — plus `PlotArea::row_at()` for naming the row a pointer is over.
 
+A figure row can hold **several plots side by side**, which the host's horizontal split needs and
+the library had no concept of: `Figure(std::span<const u32> cells_per_row)` builds one, with
+`plot_count()`, `cells_in_row()`, `first_plot_of_row()` and `row_of_plot()` to move between rows and the
+flattened plot index, `set_cell_weights()` and `set_col_gap()` to size the cells, and `FigureLayout::cells`
+(one rect per plot, flattened) and `FigureLayout::col_gap` to read the result back. `Figure(u32 rows)`
+still means one cell per row, so every row-only caller and test is unchanged, and `row_count()` stays the
+number of *figure rows* (the host's `RowSet::row_count()` is the plot count, `figure_row_count()` the
+rows). `plot(i)`, `link_x()` and the crosshair's hovered index all take the **flattened** plot index.
+Cell widths use the height scheme: a floor of **64 px logical** per cell, the weights share the rest,
+the last cell closes the row exactly, and a figure too narrow for the floors shrinks the cells
+proportionally and drops the column gap. The x labels and title follow the **column structure**: a row
+hides its x strip (`XStrip::None`) only when the row directly below has the *same columns* (same cell
+count, same normalised cell weights within 1e-4, empty weights = equal), so `[1][2]/[3][4]` has an axis
+under 3 and 4 only while `[1][2]/[3]` has one under 1, 2 and 3; the rule is structural, transitive down a
+chain and decided before the measurement pass (`same_columns()` in `figure.cpp`); `set_x_labels_only_on_bottom(false)`
+labels every row. The left y gutter stays one maximum over the whole figure.
+
+The cells of a figure row can **share one y range**, symmetric to the x link
+(`docs/superpowers/specs/2026-11-03-split-shared-y-design.md`):
+
+- `Figure::set_share_row_y(bool)`, default off so every existing figure and `tests/test_figure.cpp`
+  read as before; the host turns it on in `RowSet::rebuild_all()` before the cells are populated. When
+  on, the cells of each figure row form an implicit y link group, rebuilt with the cells.
+- Link semantics: `layout()` runs a `sync_y_links()` that adopts a member's changed `y_range` as the
+  group's and pushes it to the others, so a wheel, pan, box zoom or axis drag (all `set_y_range`) needs
+  no controller change; a manual `set_y_range` on a member clears the group's auto flag. A member's own
+  autoscale is suppressed and the group owns the flag: it fits to the union of its members' visible
+  traces (cells with no trace are ignored; a log axis takes the union in axis space), and `fit_all` and
+  a double-click fit the group, not one cell. The group only follows on a laid-out frame, so a caller
+  that sets a range or a fit and reads it back needs one `layout()` in between.
+- `YStrip {Both, None}` and `Plot::set_y_strip_mode`, mirroring `XStrip`: `None` forces the y label
+  width, title width and reserved floor to 0. `Figure::layout` sets `None` on every cell but the first
+  of its row, structurally from the column index and never from content, and skips `None` cells in the
+  common-gutter maximum. A y axis drag can therefore start only in the leftmost cell.
+- **Cell placement is by plot width**: the row's y gutter comes off the row width first, then the cells
+  share the rest by the existing `floor + extra * w / total` rule, the floors applying to plot widths.
+  Equal weights give equal plot areas; the first cell's rect is gutter plus its plot width and the rects
+  still tile the row exactly.
+- **The right gutter belongs to the last cell.** In a shared-y split row only the last cell gets
+  `set_right_gutter()`; it is taken off the row beside the y gutter (capped so both fit in half the row
+  and never beyond the figure's right gutter) and the last cell's rect grows right by it. The gap between
+  two plot frames is then exactly `col_gap` rather than `col_gap` plus a gutter; unsplit rows and rows
+  with sharing off lay out as before (`figure_split_row_gap_*`, `figure_row_gutter_without_sharing_is_the_old_layout`).
+
+In the GTK4 and GLFW adapters the pointer is routed by **cell rect** (`row_in(rows, x, y)`: the
+containing cell, else the nearest by squared distance), one `input::Controller` per plot. The tests are
+the `figure_cell*` cases in `tests/test_figure.cpp` and `glfw_host_routes_by_cell`.
+
+`plot::data::RingBuffer` carries two writes a plain SPSC ring has no use for and this app
+does: `amend(absolute, v)` rewrites a retained slot when a late packet's data finally
+arrives, and `clear_to(absolute)` empties a ring and **resumes its count at a given
+origin**. The second exists because a math channel's ring is recomputed from its inputs'
+*retained* window: `clear()` would restart it at 0 and leave every absolute index —
+`base()`, `produced()`, `copy_from()` — short by that window's base, which is the
+desynchronisation `live_window_locked()` then reads as an empty window (see
+[invariants-math-channels.md](invariants-math-channels.md)). Its guards are
+`ring_clear_to_resumes_the_absolute_count` — a derived ring refilled from a source's retained
+window must come back with the source's own `produced()`/`base()` — and
+`ring_clear_to_zero_is_clear`.
+
 The render-quality work went there for the same reason: `kTextFS` now **filters** the
 glyph atlas (a 2×2 bilinear clamped to the instance's own cell) instead of point-sampling
 it, and `LineProgram::set_snap()` / `u_snap` rounds an axis-aligned segment's ink onto

docs/claude/invariants-data-path.md

@@ -20,7 +20,7 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   comparison on purpose: it is not a size, but it is what the slots *mean*, and keeping samples
   under a changed `base_dt` would re-date the whole ring.
   **Construction is the cost.** A `RingBuffer<T>` holds a `std::vector<std::atomic<T>>`, which is
-  value-initialised, so making a store touches every byte of `--buffer-mb` — about a second per
+  value-initialised, so making a store touches every byte of the planned rings — about a second per
   gigabyte, mostly first-touch page faults — while `reset()` is one relaxed store per ring plus an
   `invalidate()` and an epoch back to zero. It must leave nothing of the old history behind, which
   is why it clears the time ring, the absolute-time ring, every value ring, and both the published
@@ -65,8 +65,8 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   trade and is why the status line's `rate` field is worth reading.
 - **A file is ingested too, so the loader decimates by the same factor.** `load_waveform_into_model()`
   sets the target span to the recording's own length and enables every column, and the plan that
-  comes back may well decimate: 20 s of 10 channels at 500 kS/s is 480 MB of rings, and the budget is
-  `--buffer-mb`. The loader therefore reads `partition().time_stride` **after** the enables and pushes
+  comes back may well decimate: 20 s of 10 channels at 500 kS/s is 10 M samples a channel, and the budget is
+  `--buffer-samples` (rounded down to a power of two, 8.39 M by default). The loader therefore reads `partition().time_stride` **after** the enables and pushes
   one slot per that many rows, carrying the group's mean at the group's mean stamp — the packet path's
   filter, written a second time because a file does not arrive in packets. Pushing every row instead
   overruns the ring and leaves the file as **its own tail**, with nothing to say so: a 20 s event
@@ -94,6 +94,18 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   comparison is off by 1e9, so every packet would read as an implausible jump. The guard is
   `tools/mock_udpstreamer.py --time-glitch-at`/`--time-glitch-by` (see
   [verification.md](verification.md)).
+- **A *restarted* client is the other way into the same poisoning, and it is not a glitch.** Going live
+  from a file view starts a new `udps_client`, and the new stream's stamps can sit **behind** the ones the
+  old stream left in `last_stamp_` — the file view's samples are still in the store. The advance test then
+  rejects every packet of a perfectly good stream, four rejections abandon the declared time signal, and
+  the arrival clock derives its epoch from the stale mark: every sample is stamped **flat at the old
+  value**. `trig engine: … ring=[2.5200..2.5200] n=567000 → n=1131000 → n=1689000` is what that looks
+  like — the count climbing at the stream's rate while the retained span is one value — until some later
+  rebuild resets the store, which is where the "few seconds of nothing" came from.
+  `Acquisition::start()` therefore calls `ScopeModel::reset_stream()` and re-bases `last_stamp_` to
+  `-infinity`: a started or restarted client is a *new stream*, so the previous one's history goes (which
+  is what `reset()` is for) and the monotonic guard re-bases on the new clock instead of pinning it.
+  `ring` moving within a stream round-trip of *Go live* is the assertion.
 - **The arrival-clock fallback does not drop history.** `arrival_epoch_` is derived from
   `last_stamp_`, so the arrival clock *continues* from the monotonic mark and the two
   timelines share a zero by construction — the recorded stamps are therefore still on one
@@ -157,7 +169,36 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
     (`kGlitchPackets`, 256) is counted in **packets, not samples**, so one hole's sample cost
     is `256 × batch_` and scales with the stream's batch — 25 600 samples at a batch of 100,
     2.56 M at a batch of 10 000 — which is the number to weigh against the ring, not the 256.
-  - **A re-plan drops every hole and restarts the producer's tick.** `rebuild_locked()` replaces
+  - **A reservation is weighed against the wire, and never booked on the counter's word alone.**
+  The counter is a *claim* about the stream; the arrival clock is a *measurement* of it, and only
+  the two together justify writing NaN into the ring (`Acquisition::gap_plausible()`, called
+  before anything is booked *and* before relative mode's own clock advance, because the advance
+  and the reservation are the same claim). Two tests, either one refusing is enough:
+  - **The arrival clock.** `missing` packets would have taken `missing` frame intervals to arrive,
+    so a gap whose elapsed arrival time is under half of that is refused. Half and not one because
+    the socket clock jitters and a drain can compress two frames' arrival times -- and a refused
+    gap costs a *shading*, never data, so the test is deliberately permissive.
+  - **The ring.** `missing × batch_` samples become `missing × batch_ / time_stride` slots, and the
+    hole may not lap `time_capacity`. This is the *sample* form of the rule the 256-packet cap
+    states in packets -- the cap's own comment says 256 packet spans in one go is an outage, and
+    the invariant above says the number to weigh against the ring is `256 × batch_` and not the
+    256 -- and it has to exist in samples because a hole that laps the ring erases the history it
+    is meant to annotate, can never be backfilled (its slots are already overwritten) and is never
+    forgotten (`forget_holes_before()` waits for slots the ring has passed), so it leaves a
+    *permanent* band over a buffer that is all NaN.
+  What its absence looks like, which is why it is written down: a device whose counter counts
+  *samples*, or frames of an inner layer, reports a forward jump on every datagram while the wire
+  delivers on time. Every frame then reserves, and with `relative_time` every frame books NaN
+  slots by construction -- one band over the whole window with the samples washed out,
+  `backfilled=0` (no packet was ever missing, so nothing can repair it), and the status bar reading
+  `live` at the right rate the whole time. The refusal is counted in `StreamStats::gaps_refused`
+  and said once per connection with the numbers, because the status bar's `gaps` climbs either way
+  and the state is otherwise invisible; `tools/mock_udpstreamer.py --counter-step N` is the mock
+  shape (its counter is otherwise always +1, so this is the one wire shape it could not produce),
+  and `gaps_refused` rising while `nan_slots` stays 0 is the reading. A refused gap is not a silent
+  one: the timeline is not stretched over loss that did not happen, so it shows as the x
+  discontinuity it is.
+- **A re-plan drops every hole and restarts the producer's tick.** `rebuild_locked()` replaces
     the store, so `produced()` restarts at 0 and a hole's `slot_begin`/`tick_begin`/`x_begin`
     describe a buffer that is gone; it therefore clears `holes_` and bumps
     `ScopeModel::plan_generation()`, which the producer compares against the value it last saw
@@ -165,9 +206,36 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
     `backfill_from()` derives a slot index from — without it the amend falls outside the ring
     and repairs nothing while the hole is still marked repaired, a band saying the opposite of
     the truth. The generation is the signal and the stride/channel-count comparison is not: a
-    reconnect with an identical CONFIG rebuilds the store leaving both unchanged. `slot_base_`
-    is **not** reset — it is relative mode's clock origin, samples since the stream began, and
-    relative time must not jump backwards when the user retypes the window.
+    reconnect with an identical CONFIG rebuilds the store leaving both unchanged.
+- **The relative clock is accumulated in *seconds*, and a frame is only stamped into a model that has a
+  streamed channel.** Relative time's stamp is the declared interval counted from the stream's own
+  origin — `Acquisition::rel_base_s_`, which is advanced by the frame's own samples and by the samples a
+  reported gap spans. It is deliberately **not** `position × Partition::base_dt`, and the difference is
+  one defect: a plan is rebuilt whenever the channel list changes (a CONFIG, an enable/disable, a
+  session's math channels), and `base_dt` is the **1 kHz fallback** until a *streamed* channel declares a
+  rate. Recomputing from a position made a plan that *shortened* the interval put every later stamp
+  behind the one already written, and the frame loop's monotonic clamp then held the clock there for the
+  rest of the run. What that looks like: `ring=[a..a]` standing still while `n` climbs,
+  `history` never reaching the pre-window (so a trigger never latches and the display stays in `Waiting`,
+  which is blank), and — the reading that names it — `[udpscope] warning: the clock stalled ...`, printed
+  once per connection the first time a whole frame's stamps are all behind the clock. Accumulated, a plan
+  change is only a slope change and the clock cannot go backwards. The entry is the *other* half: the
+  ingest used to accept a frame as soon as `channels()` was non-empty, and a session's math channel
+  applied before the stream's own signals arrive is exactly one channel with a fallback plan. Such a
+  frame has nowhere to go (the value loop skips every derived channel) and its plan's interval is not the
+  stream's rate, so `on_data()` now requires a **streamed** channel and drops the frame otherwise, the
+  same way it always did for an empty list. `rel_base_s_` is **not** reset across a reconnect — the
+  origin survives, it is relative mode's clock origin — while `base_dt`'s *use* is what this rule took
+  away: it is read to *advance* the clock, never to recompute where the clock already was.
+- **The stream's epoch is adopted *once per connection*, and "unset" is a state, not the value zero.**
+  `epoch` is the stream time the display's x = 0 means, taken from the first frame's stamp. The test for
+  "not adopted yet" used to be `model.epoch() == 0.0`, which relative mode breaks by construction: its
+  first frame is stamped exactly `0`, so the *second* frame adopted the origin — and with
+  `rel = max(stamp - epoch, last_stamp_)` that put a whole frame's samples on one stamp and shifted every
+  later x by a frame's span. `Acquisition::epoch_adopted_` is the flag, re-armed by
+  `reset_session_state()` because a new session's clock is a new clock; the warning line above is what
+  caught it.
+
 - **A dropped time slot is clamped, never answered with a sentinel.** `acquire()` pins
   the published window to the value ring's base and both rings keep sliding afterwards —
   their capacities are equal, so there is no slack — which means the oldest few samples
@@ -253,8 +321,8 @@ already scaled against, and re-anchoring mid-stream would move x. The clock *cho
 per connection (`time_source_ = 0` on CONFIG) for the same reason: a session that dropped may
 come back with a different answer.
 
-Relative time's `slot_base_` also survives: it is samples-since-the-stream-began, the user's
-chosen origin, and must not jump backwards because the link blipped.
+Relative time's clock (`Acquisition::rel_base_s_`, seconds accumulated at the declared interval)
+also survives: it is the user's chosen origin, and must not jump backwards because the link blipped.
 
 ## There may be no store at all
 

docs/claude/invariants-gtk-and-chrome.md

@@ -1,6 +1,6 @@
-# Invariants: GTK traps, the status bar, the icons and the help
+# Invariants: GTK traps, the status bar, the icons and the manual
 
-The GTK signal-signature and dialog-lifetime traps this app has already fallen into, plus the status bar's two tiers, the bundled icons and the help pages.
+The GTK signal-signature and dialog-lifetime traps this app has already fallen into, plus the status bar's two tiers, the bundled icons and how the Mallard manual is installed and opened.
 
 Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to learn; read the ones touching the area you are editing before you edit it.
 
@@ -49,58 +49,26 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   one of them with reality): it is computed on the first *tick*, because the dump
   runs after the window is destroyed and asking GTK about a widget then is four criticals, which is
   how the first version of that line earned them. What stays in the menu is what acts on the *data*
-  (Fit, Export) and the two editors that are not panes (Layout, Signal list). The Arm/Disarm button in the trigger panel still has text.
-- **Seven of this app's icons are its own, and they are a `GResource` compiled into the
+  (Fit, Export, Configurations) and the one editor that is not a pane (the layout editor): the signal list
+  is the `signals` slide-over page, so there is nothing left to reveal or hide about it. The Arm/Disarm button in the trigger panel still has text.
+- **An overlay handle that follows what it drags reports gesture offsets in its own moving
+  coordinates; add its displacement back.** A `GtkGestureDrag` measures its offset from where the
+  press began *in the widget's own coordinates*. The layout editor's column handle sits on the
+  divider and `sync_layout_editor()` moves it every frame, so after a few motion events the
+  offset is the pointer's travel **minus** the handle's travel, and the divider converges on half
+  the pointer's travel (`D = P - D`). Record the handle's x in the overlay's coordinates at
+  begin (`gtk_widget_compute_point`) and add `handle_now - handle_begin` to the offset on every update
+  (`layout_col_total_offset()`). The same applies to any future handle that is repositioned
+  from the state its own drag changes.
+- **Six of this app's icons are its own, and they are a `GResource` compiled into the
   binary.** No icon theme has a glyph for an oscilloscope trigger, a pair of cursors or a
   measurement ruler, and the stock names those buttons used to carry said something else
   entirely: a *record dot* for the trigger and three different **magnifiers** for cursors,
-  measurements and math. `src/icons/scalable/actions/udpscope-{trigger,cursors,measure,math,events}-symbolic.svg`
-  are the five action icons; beside them in `src/icons/scalable/apps/` are the two
-  **application** icons, `org.udpscope.app.svg` (128px colour artwork) and
-  `org.udpscope.app-symbolic.svg` (16px). The `apps` context is where an icon theme keeps an
-  application's own icon and is where the **in-process** window icon resolves from; it is also
-  the layout that `cmake/install_desktop_entry.cmake` mirrors when it copies the same two files
-  into `$XDG_DATA_HOME/icons/hicolor/scalable/apps` and `.../symbolic/apps` — those installed
-  copies are what makes `Icon=org.udpscope.app` in the desktop entry resolve (a desktop shell
-  cannot read a GResource compiled into the binary).
-  All six are bundled by `src/icons/udpscope.gresource.xml` (CMake runs
-  `glib-compile-resources`) and reached through **one**
-  `gtk_icon_theme_add_resource_path()` in `run_ui()`, right after `adw_init()` — not at the top
-  of `build_toolbar()`, where it used to be: there are two consumers now (the window's own icon,
-  set before the toolbar is built, and the toolbar's buttons) and `run_ui()` is the one place
-  ahead of both. `adw_init()` calls `gtk_init()`, which is what makes
-  `gdk_display_get_default()` valid there.
-  A resource rather than files beside the binary because udpscope is run straight out of the
-  build tree and has no install step. Five authoring rules, each of which fails quietly:
-  * **GTK's symbolic recolour only reaches `fill` on `path`, `rect` and `circle`.** It wraps the
-    SVG in a stylesheet for those selectors, so a `stroke`, a `line` or a `polyline` keeps the
-    colour written in the file and stays dark on a dark theme. **In a symbolic icon everything is
-    therefore a filled `path`** — including anything that wants to look stroked, which is drawn as
-    a closed band (two offset curves joined) instead. The rule is scoped to symbolic icons on
-    purpose: `org.udpscope.app.svg` is 128px colour artwork that is never recoloured, so it strokes
-    its sine freely, which is the sane way to draw a smooth one. Do not "fix" one to match the
-    other.
-  * **Whole-pixel coordinates**, because these are drawn at 16 px far more often than not: the
-    first draft placed features on half-pixels and the whole icon was a grey smear at 1x.
-  * `fill-rule="evenodd"` is how the ruler's body is a hole *and* its ticks still fill -- a tick
-    inside the hole is three crossings deep, which is odd. Nonzero would fill the hole back in.
-  * Overlapping subpaths under the default nonzero rule must be **wound the same way** or they
-    cancel instead of uniting. All of them run clockwise.
-  * **A malformed SVG is a build error, and that is the only place it can be caught.** Every
-    `<file>` in `src/icons/udpscope.gresource.xml` carries `preprocess="xml-stripblanks"`, which
-    makes `glib-compile-resources` pipe it through `xmllint` — so `--` inside an XML comment, which
-    is illegal and which librsvg refuses the whole file for, fails the build with a file, a line
-    and a caret under the offending character (`…app-symbolic.svg:5: parser error : Double hyphen
-    within comment`). It has to be here because **no runtime check can see it**: librsvg refuses
-    the file but the icon *name* still resolves, so `gtk_icon_theme_has_icon()` returns true and
-    the icon draws nothing. `gtk_icon_theme_lookup_icon()` cannot tell either (see the `app icons:` line under
-    Verification), `GMarkup` accepts the double hyphen because it is a lenient subset parser, and
-    `gdk_pixbuf` goes through glycin here, which sandboxes a subprocess per load and refuses this
-    project's own icons outright. The cost is that the `xmllint` binary is a build dependency; it
-    ships with libxml2, which GTK already requires.
-  `gtk_icon_theme_has_icon()` is checked for every toolbar button and reported by the dump (see
-  `toolbar icons:` in [probe-readings.md](probe-readings.md)): a resource path that was never added does not raise an
-  error, it draws `image-missing`.
+  measurements and math. `src/icons/scalable/actions/udpscope-{trigger,cursors,measure,events,resize-rows,resize-cols}-symbolic.svg`
+  are the six action icons. `udpscope-math-symbolic` left with the toolbar toggle that was its last
+  user; `udpscope-measure-symbolic` **stayed**, because the Preferences window's Plot page carries it --
+  an icon with a live user is not an orphan, whatever the toggle that introduced it did -- and it is
+  the Preferences window's icon and the **Dock toggle's** (the ruler: the dock is the readouts).
 - **A shortcut table row's `accel` is GTK accelerator syntax, and a pointer gesture has
   none.** `src/shortcuts.cpp`'s strings are handed to `AdwShortcutsItem`, which parses them
   with `gtk_accelerator_parse()` — so they are `"space"`, `"<Control>e"`, `"<Control>slash"`,
@@ -129,19 +97,35 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   tick updates it, so a rebuild is a per-frame relayout of a widget on screen.
   `update_status_popover()` only ever calls `gtk_label_set_text()`, and `popover_rebuilds` in
   the dump is the assertion.
-- **The About dialog, the help window and the shortcut overview are opened by `show_about()`,
-  `show_help()` and `show_shortcuts()`, and each closes with the matching call.** There is
-  exactly **one `GtkWindow`** among the three — the paged help window. It closes with
+- **The About dialog and the shortcut overview are opened by `show_about()` and `show_shortcuts()`,
+  and each closes with the matching call; the manual is *not* one of these.** `show_help()` hands
+  the `help:<document>` URI to the desktop help viewer (`GtkUriLauncher`, i.e. Yelp) — a process of
+  its own that cannot be closed from here — because the manual is a Mallard set installed for the
+  freedesktop `help:` URI, not a GResource in this binary (see the help bullet below). So there is
+  exactly **one `GtkWindow`** among *that pair*: the shortcut overview. It closes with
   `gtk_window_close()`, which emits `close-request` so the handler that nulls the file-scope
   pointer runs. `gtk_window_destroy()` does **not** emit that signal and must not be used — the
   math dialog fell into exactly this trap, and the pointer then points at a dead widget until the
-  next attempt to open the same window. The other two — the About dialog (an `AdwAboutDialog`)
-  and the shortcut overview (an `AdwShortcutsDialog`) — are **`AdwDialog`s and not `GtkWindow`s**:
-  they close with `adw_dialog_close()` and clear on `::closed`, there being no `::close-request`
-  on an `AdwDialog`. Both share one `on_dialog_closed()` handler keyed by a **pointer to the
-  pointer** it must null (`&g_about`, `&g_shortcuts`), which is what keeps one handler honest for
-  two dialogs. One `GtkWidget*` (or `AdwDialog*`) per window, nulled in its own close handler, is
-  the shape that prevents the double-open defect across all three.
+  next attempt to open the same window. **A `close-request` handler's return value is load-bearing
+  too, and its absence is silent**: the signal is `gboolean`, `TRUE` means "handled" and suppresses
+  the default handler that destroys the window, and `G_CALLBACK` is a cast — so a `void` lambda in
+  the slot compiles without a warning and GTK reads whatever the compiler left in the return
+  register as the verdict. The Configurations dialog (`open_configurations()`) was written that
+  way, and the built binary returns non-zero from the lambda, so **both its Close button and the
+  window manager's close button emitted `close-request`, were told "handled", and the dialog stayed
+  up** — "the configurations dialog cannot be closed", which no reading of the callback's type can
+  see. Every `close-request` handler therefore returns `FALSE` explicitly (the chooser's
+  `on_chooser_close()`, the overview's `on_window_close()`, the math dialog's, and this one). The About dialog (an `AdwAboutDialog`) is an **`AdwDialog`
+  and not a `GtkWindow`**: it closes with `adw_dialog_close()` and clears on `::closed`, there being
+  no `::close-request` on an `AdwDialog`. It shares one `on_dialog_closed()` handler with the About
+  pointer, keyed by a **pointer to the pointer** it must null (`&g_about`), which keeps the handler
+  honest without knowing which dialog it is. One `GtkWidget*` (or `AdwDialog*`) per window, nulled
+  in its own close handler, is the shape that prevents the double-open defect. `close_help_windows()`
+  (misnamed now) closes just the two dialogs; a failed *launch* is reported by the launcher's own
+  callback with a `GtkAlertDialog`, so a click that cannot open the manual says so. That callback is
+  also `show_help()`'s **optional reporter** (`std::function<void(bool ok, const std::string& error)>`)
+  — the one hook that runs on the success path, where no window of ours is left to observe; the probe
+  uses it and nothing else does.
 - **`build_info.cpp` is generated, never committed.** `cmake/write_build_info.cmake` runs at
   configure time (so `add_executable` can name the file) and again on every build through
   `udpscope_build_info` (so the commit and the timestamp belong to the binary that is running).
@@ -155,19 +139,90 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   arrives with `Mod::Shift` set. Ctrl+Alt together zooms neither axis, which needs no special
   case. The guards are `deps/plotter`'s own `ctrl_plus_zooms_only_x` and `alt_plus_zooms_only_y`
   tests, plus `UDPSCOPE_PROBE_ZOOMKEYS_MS`.
-- **A help page is one `.txt`, one `<file>` line in the GResource manifest, and one `kPages`
-  row.** The bodies are Pango markup in a second GResource (`--c-name=udpscope_help`, so its
-  generated symbols cannot collide with the icons'), validated with `pango_parse_markup()` at
-  load; a page that fails either lookup or parse renders a one-line stand-in and is excluded from
-  `parsed`. `UDPSCOPE_PROBE_HELP_MS`'s `parsed` must equal `pages`.
-  A page may also carry screenshots (`HelpPage::images`, a null-terminated list of resources).
-  They are `GtkPicture`s **with a height request**: one created `can_shrink` asks for *no* height
-  at all inside a box, so without the request it is allocated nothing and the page renders its text
-  with a silent gap where its screenshots should be — which is what the first version did.
+- **A help page is a Mallard file, and the manual is *not* in the binary.** `help/C/<id>/` holds
+  `index.page`, one `<topic>.page` per subject, and the `figures/*.png` the pages link, and the
+  whole set is installed (the `install()` rule in CMakeLists) to `<datadir>/help/C/<id>/` — the
+  path the freedesktop Help System Specification's `help:` URI resolves `help:<id>` to. The
+  document identifier is *derived from the desktop file's basename* (`org.udpscope.app.desktop.in`
+  → `org.udpscope.app`), so it is the `.desktop` name, the GApplication id and the install
+  directory at once; `UDPSCOPE_HELP_NAME` and `UDPSCOPE_HELP_DIR` are compiled in from that one
+  place. `show_help()` opens `help:<id>` with `GtkUriLauncher` (Yelp runs in its own process, so
+  nothing here holds a pointer to it), and its failure callback shows a `GtkAlertDialog`. That
+  failure is **careful about which thing is missing**: `gtk_uri_launcher_launch_finish()` reports a
+  launch that could not be handed over — the *handler's* absence — and cannot tell that from a
+  document that was never installed, so `help_installed_path()` walks the specification's own
+  `$XDG_DATA_HOME/help/<lang>/<id>/` then `$XDG_DATA_DIRS/help/<lang>/<id>/` for an `index.page` and
+  the dialog says which one it is: with the manual there, install a viewer (for example `yelp`); with
+  it absent, the identifier and the install command, the **system-wide** form first
+  (`cmake -DCMAKE_INSTALL_PREFIX=/usr .. && sudo cmake --build build --target install-help`), the
+  no-root `install-help-user` second with its caveat (see the location rule below) — and a
+  viewer as well, the second possibility the error alone cannot rule out. Reporting a missing
+  *document* as a missing *handler* is the defect that shape avoids.
+
+  `UDPSCOPE_PROBE_HELP_MS` launches it too, and its `[help] launch attempted= done= ok= error=''
+  installed=` line is the reading — `ok=1` is the URI handed to a viewer and not a window on screen,
+  since Yelp is another process and cannot map one headlessly; `installed=` sits beside it because a
+  failing `ok=0` has to be read against whether the document was there at all.
+
+  `UDPSCOPE_PROBE_HELP_MS` no longer parses pages — they are files, not markup in a resource — so
+  its `[help]` line asserts the set is *there*: `topics` (the `.page` files other than
+  `index.page`), `index`, and `figures`, scanned from `UDPSCOPE_HELP_DIR`. `topics=0 index=0` means
+  the manual is missing from the tree, which is the finding the old `parsed != pages` used to name.
+  `cmake --build build --target test-help` checks the set the way `test-ui` checks the `.ui` files:
+  `yelp-check`'s offline subcommands (links, media, orphans, ids) and a `yelp-build html` render.
+  `yelp-check validate` is deliberately absent — it fetches the Mallard RelaxNG schema over the
+  network and fails offline for that reason, not for a fault in the pages. The figures come from
+  `tools/make-help-shots.sh`, which drives the app headlessly against the mock and annotates a grab
+  (GTK4 must be forced to the Cairo renderer, `GSK_RENDERER=cairo`, or the X11 surface reads back
+  blank). Mallard is translatable with `itstool`, but there is no i18n set-up here: only the `C`
+  set is authored.
+
+  **A user-local help set is one Yelp cannot draw the figures of, so the system-wide install is
+  the one to recommend — and this is a *location* rule, not a markup or a file rule.** Yelp
+  sandboxes its WebKit subprocess, and that sandbox exposes the system help directories
+  (`/usr/share/help`, `/usr/local/share/help`) but not `$XDG_DATA_HOME/help`: the pages load,
+  their `<media>` figures do not, because each figure is a *separate file* the page references
+  rather than something embedded in it. The symptoms read as anything but a location problem —
+  opening a page *as a file* renders it with no images, and opening it through the app's `help:`
+  URI leaves the viewer spinning **for ever**, the failed image fetch meaning the page's load
+  event never fires while the sidebar title still updates, which looks like a navigation failure
+  rather than a missing resource. A shipped GNOME page that carries a figure
+  (`/usr/share/help/C/accerciser/api_browser_plugin.page`) draws either way, which is what
+  isolates the cause to where the set *lives*. `make install-help` (into `/usr/local`) followed
+  by `yelp /usr/local/share/help/C/<id>/<topic>.page` works; the same set under
+  `~/.local/share/help` does not. Two genuine defects were chased and fixed before the location
+  was found — a `<figure>` with no `<desc>` and a `bKGD` chunk the PNG spec forbids on an
+  alpha image — so do not read a figure that will not draw as a repeat of either, and do not
+  revert those fixes: this is why both the failure alert in `src/help_window.cpp` and the
+  manual's own `overview.page` name the system-wide install first and state the user-local one's
+  caveat beside it.
+- **The chooser carries the same help affordances as the window, and the tour request crosses as a
+  value — not a global.** The source chooser runs *before* `App` exists, so a user who has not started
+  yet is the one least able to find the help; its header bar therefore has a help `GtkMenuButton`
+  (the `.ui` holds the button, code holds the rows) whose three entries are the window's Help view's
+  the same way — `ui_impl::menu_button()`/`menu_toggle()`, the app's own row shape — with the
+  `.udpscope-menu` class on the popover. That class's rules only exist once `install_css()` has run, so
+  `choose_source()` calls it before building the rows (`install_css()` is idempotent precisely because
+  it now has two callers; the app's `on_activate()` still calls it and is a no-op by then). The rows
+  show **no accelerators**: the window's Help view prints `F1`/`Ctrl+T` because the window binds them,
+  and this dialog binds none, so a key printed here would be documentation that does nothing.
+  *Documentation* calls `show_help()` straight from the chooser (the manual is another process and
+  needs nothing of the app); *Enable contextual help* writes the settings file, which is what the app
+  reads when it starts a moment later, and **re-syncs this dialog's own "(i)" rows** through
+  `chooser_help_sync()`; *Guided tour* starts a tour **of this window** -- the chooser's own walk --
+  and that walk's last stop sets **`Config::tour_pending`**, the one value `main()` owns and hands to
+  both `choose_source()` and `run_ui()` (`open_waveform` and the preferences' relative time cross the
+  same way). `on_activate()` schedules `tour_start_requested()` 1.5 s later, the same delay the
+  first-run auto-start uses, and **that callback is separate from `tour_autostart()` on purpose**: it
+  sets `tour_requested`, not `tour_auto_started`, so `help layer:` says which of the two started the
+  window's half instead of conflating a user's request with a first run. The chooser's half has its own
+  entry points in `source_dialog.cpp` (`chooser_tour_begin`, `chooser_tour_autostart`), and *that* walk
+  is what a first run meets first -- see the tour bullets in the help-affordance section below.
 - **A `GtkPaned` hands its start child at least its minimum unless the position says otherwise.**
-  Putting the events pane in a paned is what makes its width the user's to drag -- but with the
-  position left alone, `shrink-start-child` or not, the pane's minimum is reserved as an empty column
-  while it is *closed*, and the plot pays for a pane nobody opened. The position is the only knob that
+  (The events pane that taught this is gone -- its list is a slide-over page now, with no divider -- but
+  the rule holds for any paned.) With the
+  position left alone, `shrink-start-child` or not, a closed side child's minimum is reserved as an empty
+  column, and the plot pays for a pane nobody opened. The position is the only knob that
   says "no room": store the width when it is closed (reading `gtk_paned_get_position()` *before*
   zeroing it) and set 0, restoring it when the pane opens. `gtk_paned_set_shrink_start_child(TRUE)` is
   still needed, or the minimum would clamp even a zero position.
@@ -175,13 +230,68 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   = FALSE` makes both the revealer's minimum and its natural size zero -- and its box then hands it
   everything the expanding sibling beside it did not claim, so a *collapsed* pane reserved a
   310-pixel empty column between the window edge and a plot drawn 630 pixels wide in a 1270-pixel
-  window. Every vertical revealer in the side panel hides this, because there the leftover goes down
+  window. (That pane was a revealer beside the plot; it is a slide-over page now, so no revealer sits in
+  a horizontal box any more.) Every vertical revealer in the side panel hid this, because there the leftover goes down
   instead of across. `gtk_widget_set_visible()` is what a layout honours, so anything that must not
   take room has to be hidden and not merely unrevealed; the revealer keeps the slide while the pane
   *is* open. The allocated width is how this was found -- the revealer's own measure said 0.
+  **The sidebar is one dock now, and has no `GtkRevealer` left in it**: a single `GtkScrolledWindow`
+  (`dock_scroller`) holding only the compact **readouts** (`src/ui_dock.cpp`). It
+  replaced an `AdwViewSwitcher` over an `AdwViewStack`, whose four text tabs did not fit 320 px (and a source
+  can add more); a source kind's own panels are slide-over pages, not dock sections. The reason is the one
+  this trap teaches: full panels competing for one narrow column each left every one of them short of room.
+  The full cursors and measurements panels are now the `cursors` and `measure` **slide-over pages**, reached
+  by the readouts' **Edit** buttons, and `m` toggles `measure` (it no longer scrolls the dock;
+  `dock_show_section()` is gone); the signal list is the `signals` slide-over page, which `g` and the `+` badge
+  open. The header's Cursors toggle no longer opens anything: it only enables the cursors. A *feature's* on/off is no longer a visibility at all -- the
+  **cursors'** toggle sets its pane's **body** insensitive (and the dock's cursor grid beside it) -- the readout has nothing to show with the
+  instruments off -- and the *body* and not the pane, because the pane's heading carries its own switch
+  (see the next bullet). The **trigger's body is deliberately never disabled**: a trigger is configured
+  *before* it is switched on, so switching it off to change it, or to read what it is set to, is the
+  ordinary way to work. It used to go insensitive with the mode, which left the settings unreachable
+  exactly when a user wanted to change them; `trigger panel sensitive …=1` is the regression guard, and a
+  `0` there means the configuration has been locked out again. The
+  trap itself does not go away with the widget: a section scrolled out of view is still laid out, but
+  **ask about state, not about size** still holds for anything a tick reads.
+- **The dock is shown but insensitive until the stream has signals ("disable, do not hide").**
+  `update_side_visibility()` and the tick's per-frame block set the column's visibility from the user's wish
+  alone (`sidebar_wanted`) and the dock's *sensitivity* from `have_signals`; the toolbar's Dock button stays
+  sensitive throughout. The `cursors` and `measure` **pages follow the same condition** through
+  `update_signal_availability()` (called from `update_side_visibility()` and the per-frame block), so a
+  page opened by `m` before the stream has signals is insensitive, not refused. `[readouts] ... pages_sensitive=`
+  reads it. The wish is persisted (`dock = true|false` in the session file) and a change of it
+  schedules a save. `dock:` in the dump reads the result.
+- **The signal badge is the drag handle, and a drop handler only moves widgets.** Dragging a signal onto a plot
+  starts on its badge in the badge bar (a `GtkDragSource` on the badge's button, payload the signal index as a
+  decimal string, taken by the plot area's existing drop target); the list's rows are not drag sources. A drag
+  starting with the slide-over open would have part of the plot hidden under the panel, so the source's
+  `drag-begin` closes it (which only restyles the badges: nothing is destroyed mid-drag). A click without movement
+  never reaches the drag threshold and still opens the page; past it the source claims the sequence and the
+  button's click is cancelled. Each badge is also a `GtkDropTarget` for reordering: `on_badge_drop` calls
+  `gtk_box_reorder_child_after` and rewrites `App::badge_order` from the widgets, and **never rebuilds the badges** --
+  the dragged badge and the target whose `drop` emission is running must both survive it. A foreign drag whose string is not a
+  signal index is refused. `[sigbadges]` reads the controllers, the payload and the reorder; `pane drag:` reads the close.
+- **A stock icon name has to be one *Adwaita* has, and a blank button is the failure mode.** The
+  trigger pane's `[edit]` button is `document-edit-symbolic` (the pencil: edit) and `object-select-symbolic`
+  (the check: done). The done one was `emblem-ok-symbolic`, which breeze ships and **Adwaita does not** —
+  so the button that leaves configuration mode was blank, which no other reading could see: the button
+  worked, the layout was unchanged, and only `pane edits:` (the two names and
+  `gtk_icon_theme_has_icon()`'s verdict, clicked into each mode) would say so. Check a name against
+  `/usr/share/icons/Adwaita` before using it; a name found under `breeze` is not an answer.
+- **A pane's heading switch and the header bar's button are one control in two places.** Each pane's
+  heading (`build_trigger_panel()` builds the trigger's, `cursors-panel.ui` has the cursors' in its
+  `head`) carries a `GtkSwitch` that runs the *same action* the toolbar button runs, and
+  `sync_panel_switches()` re-reads each pair from the toolbar's state after any change — so clicking
+  either end moves both, and `panel switches: trigger=1/1 cursors=1/1` is the reading. Two traps:
+  a `GtkSwitch` emits `notify::active` for a *programmatic* write as well, so the sync holds a guard
+  (`App::panel_switch_sync`) or the program's own write comes back as a click; and the switch must
+  stay *out* of what the pane disables, because a control inside an insensitive parent cannot be
+  clicked — a switch that greyed out with its own pane could never turn it back on. That is why the
+  sensitive target is the pane's **body** (`trigger_body`, `cursors_body`) and not the pane.
 - **A list box outlives the children of the pane it sits in, and the teardown order is not yours to
-  choose.** Tearing the window down finalizes the events pane's buttons, then the list box, and the
-  list's own `selected-rows-changed` then reaches a handler holding the freed pointers: four
+  choose.** Tearing the window down finalizes the events page's buttons, then its list box, and the
+  list's own `selected-rows-changed` then reaches a handler holding the freed pointers (`update_group_buttons()`
+  therefore keeps its `app.window == nullptr` guard): four
   `Gtk-CRITICAL`s from `gtk_widget_set_sensitive` and a read of memory nobody owns. `close-request` is
   *not* the hook -- `UDPSCOPE_EXIT_AFTER_MS` ends the self-check with `gtk_window_destroy()`, which does
   not emit it. The hook that does work is `App::window`: every teardown path clears it *before* the
@@ -198,22 +308,26 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
 - **A pointer to a widget inside a list survives the list being rebuilt.** `events_thumb` named a row's
   picture across `refresh_events_pane()`, which removes every row first: the next reader of that
   pointer got a `Gtk-CRITICAL` from `gtk_picture_get_paintable` on freed memory (the four criticals
-  read as "the pane is empty"). A rebuild has to null what it is about to destroy, not only rebuild it.
+  read as "the page is empty"). A rebuild has to null what it is about to destroy, not only rebuild it
+  (`rebuild_events_pane_list()`, the page half of `refresh_events_pane()`, nulls `events_thumb` before it removes the page list's children). A handler on a
+  row that rebuilds the list destroys the widget it was emitted from: `outlive_the_rebuild(widget)`. The dock's
+  rows are a second list built from the same records; the dock row's click handler is safe only because
+  `replay_event()` never rebuilds the dock list.
 - **`gtk_picture_set_filename()` can render nothing, silently.** It hands the file to the image
   loader's sandboxed, asynchronous decoder, which on this machine fails without a message: the
   picture keeps a *paint-able* and takes an allocation, so a probe that checks
-  `gtk_picture_get_paintable()` reads success while the pane shows an empty rectangle (the event
-  pane's preview did exactly that). `gdk_texture_new_from_filename()` decodes the same file on this
+  `gtk_picture_get_paintable()` reads success while the page shows an empty rectangle (the event
+  page's preview did exactly that). `gdk_texture_new_from_filename()` decodes the same file on this
   thread and `gtk_picture_set_paintable()` hands over the result -- and a NULL texture at least says
   so. A picture that must be on screen is also a picture with a **height request**: `can_shrink`
   alone asks for no height at all in a box.
 - **A cache that is the *only* source of a widget's content must be created by the thing that reads
-  it.** The event pane's thumbnails come from an `EventThumbCache` hung off the list box with
+  it.** The events page's thumbnails (the dock's rows have none) come from an `EventThumbCache` hung off the page's list box with
   `g_object_set_data_full`, and `event_preview_texture()` answers out of that cache or not at all.
-  Nothing ever created it — so for as long as the pane existed, **every** row came up without a
+  Nothing ever created it — so for as long as the list existed, **every** row came up without a
   picture, which is what "event screenshot are unusable and sometime missing" was. A missing cache
   there is not a slow path, it is a blank one; `event_thumb_cache()` therefore creates one on first
-  use. Owned by the **list**, because nothing else has the pane's lifetime: textures of a list that
+  use. Owned by the **list**, because nothing else has the page's lifetime: textures of a list that
   no longer exists are so much held memory, and the destroy notify is where they are unref'd.
 - **Hover magnification is a tooltip, not a popover of ours.** A row's thumbnail is 138 px wide and
   the stored preview is 480: the small one says *which* event this is, and the zoom says what is in
@@ -412,3 +526,199 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
     is why every documented probe (all of them pass `--server`) is on exactly the path it was before --
     and a `--server` run never had a window to lose, so the post-present notice is the right place for it.
     `loading_hide()` is a no-op when none is up, so `run_ui()` needs no notion of which path it is on.
+
+## The help affordance layer
+
+The `Help` submenu, the contextual help's "?" and the guided tour, and the traps each of them met.
+
+- **`gtk_widget_measure()` includes the widget's own margins.** Measured: a box whose natural width
+  is 280 and whose `margin-start` is 453 reports `natural = 733`. That matters wherever a measure is
+  used to *place* the widget and the margin *is* the placement: the width the widget was placed at
+  comes back as its width, and the card of the guided tour walked between the bottom-right corner and
+  the left of the target from frame to frame because of it (a `place_natural()` that set no size
+  request did not help -- the margin alone was the loop). Take the margins off a measure that feeds a
+  position back. `hdl`/`bd`-style CSS padding is *not* part of it, and neither is the other axis's
+  margin, so it is `margin-start + margin-end` on the horizontal and top/bottom on the vertical.
+- **A widget's allocation is not `gtk_widget_get_width()`, and a measure is never a position.** GTK's
+  `gtk_widget_get_width()`/`get_height()` return the widget's **content** box: `size_allocate`
+  subtracts the CSS border and padding before storing them (measured on the tour card, which carries
+  `border 1px` + `padding 12px`: `get_width()` reads 254 where the rectangle on screen is 280), so a
+  card *placed* from it overhangs its own size and covers the target it is meant to sit beside.
+  `gtk_widget_compute_bounds()` is that rectangle -- border and padding in, margins out -- and is what
+  the probe's geometry and the help's figures already read. And `gtk_widget_measure()` cannot stand in
+  for it: its size includes the widget's margins (the bullet above), and asking for a **height with a
+  width** (`for_size`) on a widget whose margins were then subtracted from that width makes GTK warn
+  `Trying to measure GtkBox ... for width of N, but it needs at least M` **once per frame**, because
+  the for_size lands one margin short of the minimum the widget answers with. The guided tour's card
+  therefore takes its size from `compute_bounds()` once a frame has run and falls back to a measure
+  **with no for_size at all** (`-1`, the form GTK measures without that check) only on a frame with
+  nothing allocated yet. The warning reaches no probe -- GTK is built with **structured logging**, so
+  it goes through the log *writer* and never `g_log_set_handler()`/`g_log_set_default_handler()` --
+  which is why the exit dump counts GTK's own warnings through a writer function (`gtk warnings:`,
+  which must read 0) as the one reading that can assert the class away.
+- **The overflow menu's `Help` submenu is a two-page `GtkStack`, and neither of the obvious
+  alternatives works.** Rebuilding the rows -- the plot menu's own shape -- destroys
+  `app.layout_toggle`, which points into the main view and which `sync_layout_editor()` and the `L`
+  accel read; swapping the *popover's child* instead leaves whichever view is not showing with the
+  popover as its only owner, so it is finalized the moment it is swapped out. The popover's child is a
+  stack, the visible child is the view, and `gtk_popover_present()` re-measures a popover that is
+  already up. `UDPSCOPE_PROBE_MENUS_MS` walks the *visible page*, which is the one line the stack cost
+  the probe.
+- **A "(i)" joins its surface's row as a sibling, not as an overlay child.** An overlay child
+  sits *on* whatever is under it -- and every panel heading already has a switch or a pencil in a
+  corner. `src/ui_context_help.cpp` is a table of (id, title, body, shortcut, host) where the host is
+  the *row* -- a panel's heading usually, and the row of a specific control (the "record events"
+  switch, the pre-trigger share, the search block's expander *header*) where that is the thing being
+  explained. The one exception is the
+  plot, which has no heading: its "(i)" is an overlay child of the overlay the layout editor already
+  uses, and its corner is free. The icon is **`dialog-information-symbolic`** -- `help-about-symbolic`
+  is *already* the status bar's information button, and two "help" glyphs meaning different things on
+  the same line is the trap the seven app icons exist to avoid; the dump reads the name back through
+  the theme for the same reason the pane [edit] buttons do. `math_head` exists only while the math
+  editor is open, so that row is skipped when it is null.
+- **A `GtkMenuButton` ignores both `min-width` and a size request, and the icon is a node *below*
+  its `button` subnode.** The "(i)" is meant to be a *mark*, not a button, and the default is 34x34 (a
+  24 px floor plus 5 px of padding from Adwaita's `button` rule). Measured on libadwaita 1.10: setting
+  `min-width`/`min-height` on the widget changed nothing, and neither did `gtk_widget_set_size_request()`
+  -- the menu button's own measure wins. The node tree is `menubutton > button > box > image` (read off
+  the CSS node dump), so `install_css()` reaches the glyph as
+  `menubutton.udpscope-hint > button > box > image`. The direct-grandchild form `> button > image`
+  matches **nothing** and is silent about it -- the glyph keeps its natural 16 px, which is why an
+  earlier version shipped a 16x16 mark and took that for the floor it was not. Zeroing the outer node
+  and the `button` subnode and asking the glyph for **12 px** (`min-width`/`min-height` *and*
+  `-gtk-icon-size`, the latter what actually *scales* the drawing rather than clamping its box) gives
+  **12x12**. (A class on the outer node alone leaves the subnode at 34; a class on the subnode alone
+  shrank the width to 16 and left the height at 26.) There is no lower floor: the symbolic glyph renders
+  at any request (measured down to 4 px), so 12 px is a legibility choice and not a limit. The dump's
+  `hint=` reading is that number, measured with `gtk_widget_compute_bounds()` on the first *visible*
+  hint -- a hint inside a collapsed `GtkExpander`'s *child* is not in the widget-parent chain at all and
+  reads 0x0, which would look like a mark shrunk to nothing. That is why the search block's hint rides
+  the expander's **header** (a `label-widget` box, `search_head` in `src/ui/trigger-panel.ui`, which
+  *is* in the tree) rather than its child, and why the `[helpui] collapsed search:` reading asserts the
+  header hint is mapped and 12x12 while the block is collapsed.
+- **Off is gone, not greyed, and the buttons are found by a data key rather than kept in a list.** The
+  list is what the math editor cannot survive: its heading lives in a builder that is dropped and
+  rebuilt on every opening, so a stored pointer into it would go stale one dialog later. A key on the
+  button (`udpscope-help-hint`, carrying the surface's id) is both the mark that says "this is a hint"
+  and the name the probe and the dump report it by, and removing a hint is `gtk_widget_unparent()`,
+  which means the same thing for a box and for the plot's overlay. The button itself is
+  `ui_impl::hint_button()` reached either by the table's `context_help_sync()` or by
+  `context_help_button()` for a window with no `App` (the source chooser) -- one button, two callers,
+  so the two windows cannot drift into two affordances.
+- **A hint on a slide-over page's heading is attached all the time and drawn only while the page is open.**
+  The trigger's, signals', cursors' and measurements' headings (`trigger_head`, `signals_head`,
+  `cursors_head`, `measures_head`) live on pages that exist, unmapped, whether or not they are open, so
+  `context_help_sync()` attaches their "(i)" like any other and the count (`hints=12`) does not depend on
+  which page is up. There is **no second code path** and the dock's readouts carry no hint of their own: the
+  pages' hints say what the dock shows too (the cursors' and measurements' bodies mention the read-only copy
+  and the Edit button). A probe that must *see* one drawn needs its page open, like every other reading off a page.
+- **The tour has one stop for the readouts and none for the pages behind them.** The dock's stop
+  (`side`, target `side_box`, no `page`, so it closes the panel) describes the readouts, the **Edit**
+  buttons and the click on a measurement; the `cursors` and `measure` pages are reached from there rather than
+  walked. A stop for either would be one more `TourStop::page` (see the next bullet), and the plan's
+  length is asserted (`steps=6`, `steps=5` with the dock put away) -- a new stop changes both.
+- **The guided tour takes no grab, and that is the whole reason it is an overlay.** Four dim
+  rectangles around the hole are ordinary widgets that swallow the clicks that land on them and
+  nothing else; `Skip`, `Finish` and `Escape` hide them, and there is no popover, no gesture and no
+  grab to leak. The probe asserts it as a reading -- `controllers=` against the count taken before the
+  tour opened -- rather than as a claim, because "no lingering grab" is exactly the sort of thing a
+  later change can add back without noticing.
+- **Click-away coexists with the plot's gestures because the observer never claims the sequence.** The
+  slide-over closes on a press anywhere outside it, and the plot underneath already owns pan, zoom, drop and
+  right-click. A `GtkGestureClick` added to `plot_overlay` in `GTK_PHASE_CAPTURE` sees the press before the
+  plot's own controllers and **does not call `gtk_gesture_set_state()`**, so the sequence stays unclaimed and
+  the plot's gestures run exactly as before; claiming it (or putting a full-area target over the plot) would
+  swallow the very pan the click was part of. The observer decides inside/outside by
+  `gtk_widget_compute_point()` into the revealer plus `gtk_widget_contains()`, never by pick. The press
+  that closes the panel still reaches the plot, which is accepted: it is one click and not a drag the user
+  started on purpose. `[slideover]` reads `click_inside_closes=0 click_outside_closes=1`.
+- **`AdwToggleGroup` is the segmented switch** (libadwaita >= 1.7; the build asks for 1.8). It replaces the
+  `AdwViewSwitcher` for a source with several panels (the E-1608: Analog out | Digital I/O). Its toggles are
+  named by the slide-over page ids, and the group's `notify::active-name` is the *input*; writing it
+  ourselves (`slideover_open` on a source page) goes through `SlideOver::syncing`, or the program's own
+  write comes back as a click and re-opens the page it just opened. It is hidden unless a source page is
+  open and there are two or more, which `[badges] switch_visible=` reads.
+- **The tour is one implementation over two windows.** `ui_impl::TourView` holds the overlay children
+  and the walk's place in it (`tour_build`/`tour_begin`/`tour_advance`/`tour_end`/`tour_update`), and
+  what differs between the windows is only the *stops*: a `TourStop` names a widget the owner resolves,
+  so each window keeps its own table -- the main window's against `App` fields,
+  `source_dialog.cpp`'s `kChooserStops` against the `Chooser`'s. A walk that passes its last stop calls
+  the view's `on_done`; the window's passes null, the chooser's sets `Config::tour_pending`, which is
+  how the two halves are one tour. `App` carries its own `TourView` (`app.tour`), so the machinery is
+  compiled once and the probe reads either window's state by the same fields.
+- **A stop declares the page it stands on, and the tour selects that page as the stop is entered --
+  by a hook in the main window and by a stack in the chooser.** The main window has no page stack any
+  more: its pages are the slide-over's. A `TourStop::page` there is a slide-over page id (`trigger`), and
+  `TourView::on_page(page_user, page)` opens it -- or, for a stop whose `page` is null, **closes** the
+  panel, so the card never points at the status line over an open panel. `tour_end()` calls
+  `on_page(nullptr)` *only if a walk was running* (so Skip, Esc and the last Next close a panel the tour
+  opened, while dismissing an idle tour does not close one the user opened). The chooser has no hook and
+  keeps `TourView::page_stack` (an `AdwViewStack`, selected by name). `select_view_page()` is the single
+  entry for both, and `show_step()` calls it before anything is measured.
+  Two rules follow from a panel that *slides*. The page switch is **not** followed by a one-shot measure:
+  `tour_update()`, which already runs every frame, fills the spotlight in on a later one, and for a stop
+  with a page it waits for `TourView::page_settled` (the slide-over's `gtk_revealer_get_child_revealed()`)
+  -- until then the target is moving, so the surface is dimmed with an empty hole. And **the hole is the
+  target's bounds clipped by every `GtkScrolledWindow` above it** (`tour_target_bounds()`): a form taller
+  than the panel's scroller overruns it, and an unclipped hole spotlights the badge bar and the status
+  line under the panel. A target scrolled out entirely is a *measured, empty* rectangle (the function
+  returns true), not a failure -- `tour_update()` zeroes the hole on it, because taking "false" for "not
+  measured yet" keeps the previous frame's hole standing. A stack allocates a new page's widgets on the
+  frame after the switch, so a measurement taken in the switch's own tick reads zero (the allocation
+  bullet in [invariants-trigger-and-pinning.md](invariants-trigger-and-pinning.md)) -- reading the
+  page *name* back is fine immediately, because that is state and not geometry.
+- **The stop filter runs on `get_mapped()`, not `is_visible()`, and that is what separates a wrong
+  page from a collapsed pane.** GTK 4.24's `gtk_widget_is_visible()` walks only the widgets' own
+  `visible` flags up the parents; it does **not** consult `child_visible`. Both a `GtkStack`'s
+  non-current pages and `AdwOverlaySplitView`'s hidden sidebar are hidden with
+  `gtk_widget_set_child_visible()`, so a widget on another page, *and* one in a collapsed pane, both
+  read `is_visible() == TRUE` (verified against 4.24.1) -- the old filter kept a stop it meant to
+  drop and left the spotlight on a target with no allocation. `stop_is_walkable()` keeps a stop when
+  its target is **mapped**; a stop that names a page of a view with an `on_page` hook is **always**
+  kept (the hook opens the page whatever the dock is doing, since the slide-over does not depend on it);
+  and in a view with a `page_stack` a stop that names a page is kept when the stack is mapped -- a wrong
+  page leaves the stack mapped, so the page switch reveals it, while a collapsed pane leaves it unmapped
+  too and the stop is dropped. So the dock's stop is dropped in a window narrow enough to overlay it, and
+  the main window's tour is five steps there (`[toursurface] collapsed: ... steps=5`: the signals stop names
+  the `signals` slide-over page, which does not depend on the dock either). The filter
+  lives in `tour_begin()`, not in each window's `start_tour()`, so the two windows cannot drift
+  into two rules.
+- **The chooser's tour needs an overlay over its *whole* window, and `AdwWindow`'s content is
+  replaced, not wrapped.** Two of the chooser's stops name header-bar buttons, and an overlay inside
+  the `AdwToolbarView`'s `content` would give them negative coordinates and clamp the hole to the top
+  edge. So the overlay *becomes* the window's content and adopts the toolbar view -- and the order
+  matters: `gtk_overlay_set_child()` refuses a child that still has a parent, so
+  `adw_window_set_content(win, overlay)` goes **first** (that call is what unparents the toolbar view)
+  and `gtk_overlay_set_child(overlay, content)` second. The builder's object list still owns the view,
+  so nothing is finalized in between. Getting the order wrong is a `Gtk-CRITICAL` and an empty
+  chooser, which is exactly what the first version of this did.
+- **The chooser's hints are its own table because it runs before `App`.** An `AdwEntryRow` is not a
+  box and its editor is internal, so a hint cannot join the host/port fields as a sibling -- appending
+  it to the `AdwPreferencesGroup` would make it a row under the field rather than a mark beside it, so
+  no hint is invented for them and the group's own `description` carries that text. The two rows the
+  dialog *does* have -- the heading above the saved-source list and the waveforms page's action row --
+  carry `chooser_sources` and `chooser_waveform`, added with the same `context_help_button()` the
+  window uses and re-synced by its Help menu's toggle.
+- **The hole is kept from the last frame that could measure the target.** `gtk_widget_compute_bounds()`
+  answers nothing on a frame that lands between two layout passes, and letting the hole empty there
+  made the spotlight and the card jump to the corner and back; a *target that is not mapped* is the
+  different case (a genuinely absent surface) and is what empties it. The placement is also
+  re-measured on **every frame**, never once at the start: a widget's allocation is 0 on the frame it
+  is first shown, and a window resize moves it under a one-shot measurement.
+- **The first-run tour is a `settings.toml` key (`tour_seen`), written when the tour *starts*.** Not
+  "the settings file did not exist": a user who has already changed the theme has a file and has still
+  never seen the tour. Written on the way *in*, because a user who skips it in the first second has
+  still seen it. It starts **in the source chooser** when one is shown (the chooser is the surface a
+  first run meets first, and the window's own auto-start is unreachable until the chooser has returned
+  with a source) and in the window otherwise; either way it is a 1.5 s timer, so the window is up and
+  laid out before anything points at it. The chooser's walk writes the key itself and hands the second
+  half over by `Config::tour_pending`, so a first run is *one* tour that crosses the two windows.
+- **The `help figures:` line is captured on the tick, like every other size the dump prints.** It names
+  ten surfaces' window-coordinate rectangles for the help's annotated figures, and the dump runs after
+  the window is destroyed -- a `gtk_widget_compute_bounds()` there is the "no `gtk_widget_*` call in the
+  dump" rule again. `is_visible()` *and* `get_mapped()`, not `get_visible()`: a widget under a hidden parent -- the trigger
+  summary while the pane is in configuration mode -- keeps its own flag true and reads 0x0 (and a widget on a closed slide-over page, `trigger_*`
+  while the panel is shut, would read a bogus `630,46,0,0` without the mapped test), and a crop
+  box drawn from that is a box over the wrong thing. Its numbers depend on the *window's* size, which
+  under the documented `xvfb-run` is the window's 756x894 minimum (a 640x480 screen), so a run on a
+  larger screen gives different rectangles for the same panels.

docs/claude/invariants-math-channels.md

@@ -301,6 +301,17 @@ with at most the transient a re-start costs. The exit dump's `math '<name>': fin
 the assertion: `finite` must be about `M` minus the hole share, and `finite=0` beside non-zero
 `hole_slots` is this defect returned.
 
+- **A math channel is a row of the *signal* list, under a `MATH` divider, and there is no math pane.**
+  `append_math_signals_locked()` already puts every channel in `signals()`, so the pane was the same
+  list drawn twice; the divider is what the pane uniquely contributed. It is non-selectable and
+  non-activatable -- a heading that highlighted under the pointer would read as a row you can plot --
+  and it carries the `+` that creates a channel, appended even when there are none, because a `+` that
+  waited for a channel to exist could never create the first one. A math row's menu is *Edit graph…*,
+  *Default colour*, *Delete*: no Information and no Gain/Offset rows, because calibration is applied at
+  ingest and a derived channel has no stream to describe, and no rename, because the node editor owns
+  a channel's name and unit and a second place to change them would be a second answer to the same
+  question. A row's tick is the channel's own switch and must reach `App::math` -- the copy the
+  session file is written from -- or the list and the file disagree about what "enabled" was.
 - **A graph *edit* does not move the plan; adding or removing a channel does.** The plan is a partition over
   the channels, so `set_math_channels()` takes a surgical path whenever the *set* is unchanged -- same channels,
   names and enables: the store is never touched, every other channel keeps its samples **and** its runtimes, and
@@ -312,6 +323,28 @@ the assertion: `finite` must be about `M` minus the hole share, and `finite=0` b
   `[math-probe] graph edit: stored_slots N -> M` reads it: M must be at least N -- the store keeps filling
   while the edit runs -- and never 0.
 
+- **A recompute rewrites a ring *in place*, and both of the ring's counters have to survive it.**
+  `recompute_math_locked()` replays the inputs' **retained** window, which begins at the time ring's
+  `base()` and not at zero, so an emptied derived ring is restarted with `clear_to(base)` and never
+  `clear()`. With `clear()` the refill renumbered the channel from 0 and left its `produced()` short by
+  exactly `base` -- and `live_window_locked()` clamps its window against *every* channel's `produced()`,
+  so that one lagging channel answered `n = 0` for the live view, every pause view **and** every trigger
+  capture, until a whole ring of fresh data had gone by. That is the "a math edit freezes acquisition,
+  and the trigger stops firing on a channel that is not even derived" report, and it is **invisible
+  before the ring first wraps** (`base == 0`, where the two numberings coincide), which is why it reads
+  as intermittent and uptime-dependent. The dump's `math '<name>': N samples vs M time slots` is the
+  reading -- both numbers are `produced()`, so a mismatch *is* this defect -- but only on a run whose
+  ring has wrapped: give it a small `--buffer-samples`. `UDPSCOPE_PROBE_MATHWRAP_MS` is the probe that
+  arranges exactly that, and it exists because **`math_probe` structurally cannot** reach this state:
+  every edit that probe makes follows a structural change, which replans the buffer and restarts every
+  ring at absolute 0, where both halves of this are identities.
+  The published window is the second counter. `acquire()` is incremental, so a rewrite that leaves
+  `produced()` where it was publishes **nothing** and the pyramid -- what the renderer and every
+  measurement read -- goes on describing the samples the edit replaced. `ChannelBuffer::republish_from(base)`
+  is what puts it back, and it takes the ring's base rather than 0 because `invalidate()` would make the
+  next `acquire()` walk every absolute index ever produced (an hour at 1 MS/s is 3.6 G appends) to publish
+  one window.
+
 - **A math channel whose source is switched off is switched off with it.** `Source` resolves to a *channel*, so
   a derived channel cannot be computed from a signal nobody acquires: left enabled it would silently compute
   nothing, which is what "all math signals depending on it do not compute anymore" looked like from outside.

docs/claude/invariants-measurements.md

@@ -1,6 +1,6 @@
 # Invariants: the measurements pane
 
-Why the pane is refreshed on a cadence, why neither pass may read its window raw, and how a crossing is counted.
+Why the pane is refreshed on a cadence, why neither pass may read its window raw, how a crossing is counted, and which mean over a split is which.
 
 Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to learn; read the ones touching the area you are editing before you edit it.
 
@@ -16,9 +16,42 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   frame; the window is materialized in bounded chunks (never two whole-window f32 temporaries)
   and the loop holds it **by reference** (copying both vectors per measurement was 300 MB of
   memcpy a frame); and `measure_stats()` is one shared pass carrying both extremes with their
-  first positions, the sum and the count, so average/min/max/peak-to-peak/amplitude need no
-  pass of their own. **Adding a type must not add a pass** -- that is what `compute_measure()`'s
-  `stats` argument is for.
+  first positions, the sum and the count, so average/min/max/peak-to-peak need no pass of their
+  own -- `top`/`bottom`/`amplitude` take a second read of that same **bucket** list and never of
+  the window (the flat-level invariant below). **Adding a type must not add a pass** -- that is
+  what `compute_measure()`'s `stats` argument is for.
+  **The window a value is computed over is the *pin* while the view is pinned, and the viewport
+  otherwise.** A pinned view -- a held event, a paused stream, an opened file -- is a *still
+  frame*: the data behind it does not change, so a pan or a zoom only looks closer. Measuring the
+  pin (`RowSet::pinned_range()`, the same accessor `hold_pinned_window()` clamps into, so "what
+  frames this view" has one expression) is what makes a gesture change **no value at all** --
+  and it is decided in `update_measures()`, at the call site, rather than inside
+  `MeasureWindowReader`, because the decision is also *booked*: the window
+  `MeasureWindowReader` is handed is the same one the "it moved" test compares against
+  `App::measure_window`, so a gesture inside the pin spends no recompute either. A reader that
+  chose its own window would leave a pinned view recomputing on every gesture frame for a number
+  that cannot change (457 passes in one run is the shape that mistake took).
+  This test has been wrong in both directions and the reasoning is worth keeping. Suppressing it
+  while held (`moved = ... && !held`) left the pane describing the whole 2 s event
+  (`for=[0.47..2.47]`) while a 50 ms slice of it was on screen; *removing* the exemption was the
+  opposite mistake, and it is the reported "when measuring a still frame (a triggered event, or a
+  paused stream) moving the zoom makes measurements such as average or top change, which should
+  never happen". The two are one question asked of two different windows: **which window is this
+  pane about** (the pin, while pinned) and **has it moved** (asked of that window in every mode).
+  Answers: a pinned view still recomputes when it should -- a fresh latch, a re-stated pin, a new
+  snapshot, the held/live change -- and a settled one satisfies `swin == measure_window` exactly
+  and so reads `moved == false` on its own.
+  `[measurepin-probe]` is the reading: on a latched event zoomed to a quarter of itself,
+  `same=4/4 for_same=1 pass_delta=0` with the values bit-identical and `for=` still at the pin;
+  the same on a pause taken from a held event. Live is the case that must **not** be swallowed,
+  and it reads `same=0/4 for_same=0` with a positive `pass_delta`, `span_before=2.000000`,
+  `span_after=0.125000` and `follows=1` -- the results window narrowed with the viewport and the
+  values moved with it. The
+  one path that is *not* this rule is the window control: `apply_time_window()` unpins
+  (`set_time_window()` clears `pinned_`), so for the frames before the held branch re-states the
+  pin the view really is live-framed and the pane measures the viewport -- `[measure-trace]`
+  prints `pin=off` for exactly those frames, which is what makes them legible rather than looking
+  like the defect again.
   The marks' *ink* is set where they are created (`install()` in `plot_host.cpp`): 0.75 px and
   dashed 4/4 through `Plot::set_cursor_stroke()`, which is per cursor because the trigger marker
   (also a cursor) keeps the solid `line_width_px` stroke. A new measure mark must take that
@@ -57,10 +90,19 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   *finite* sample of the new side and an aggregate cannot say which that is); the caller then opens
   that bucket. **Nothing may be folded before a refusal** -- a refused bucket goes to
   `measure_accumulate()`, which adds the same samples again, and sums added above the `return false`
-  double-counted every opened bucket, reading `top=0.614304` on a unit sine against the 2/pi it must
-  be. Four things this rests on, each of which breaks it silently:
+  double-counted every opened bucket. That read as `top=0.614304` on a unit sine against the 2/pi a
+  mean over a half then gave; a *bucketed* window no longer reports `top` from those sums at all
+  (see the flat-level invariant below), which makes the rule easier to break silently rather than
+  less binding -- the sums are the fallback a window with no histogram reads, so a wrong one is a
+  wrong answer waiting for that window. Four things this rests on, each of which breaks it silently:
   * **Exactness is the point, so nothing may stride or decimate.** `peak to peak` must still read
-    exactly `2` on a unit sine and `top` exactly `0.636620` (2/pi). A bucket's sum is a sum.
+    exactly `2` on a unit sine, and it and `average` still come straight out of the one shared
+    `measure_stats()` pass. A bucket's sum is a sum. (`top` has no *exact* reading to protect any
+    more: it is a density estimate and not a mean, so the assertion that used to be
+    `top == 0.636620` on a sine now belongs to `above 50`, which *is* a mean over a side and reads
+    exactly 2/pi again -- see the band-average invariant below, and the flat-level one for what
+    `top` reads instead. Everything above is about the *bucket* path being a fast path and not an
+    approximation, and that is unchanged.)
   * **The bucket index space must be the window's.** `ChannelBuffer::acquire()` calls
     `pyramid_.drop_before(values_->base())`, so a channel's pyramid is in the value ring's
     absolute index space -- the same space `live_window_locked()` answers in, since a channel's
@@ -76,9 +118,160 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
     the pyramid for nothing.
   `measure cost:`'s `covered`/`buckets`/`raw` is the guard, and it needs the fast mock to say
   anything.
+- **A pass costs the window's buckets times the pane's *measured channels* and its *distinct
+  levels*, and the window's own size multiplies all of it.** The cadence above bounds *how
+  often*; this is *how much*, and it is the term a big time scale buys. Measured on the mock at
+  the user's scale -- a **15 s** window, `--buffer-samples 100M` (so `time_stride` stays 1 and the
+  window is 11.8 M samples, 184 k level-0 buckets), four signals, one row -- with
+  `[levels-probe]` (see [verification.md](verification.md)), `measure cost:` reading
+  `recomputes`/`each`/`covered`/`buckets`/`raw`:
+
+  | pane | `each` | `raw` | tick mean |
+  |---|---|---|---|
+  | empty | -- | -- | 1.34 ms |
+  | 1 measurement, 1 level | 6.58 ms | 0.1 % | 1.99 ms |
+  | 4 measurements, 4 shares on **one** channel | 10.28 ms | 0.4 % | 2.38 ms |
+  | 16 measurements, 16 shares on one channel | 24.55 ms | 1.2 % | 3.86 ms |
+  | 4 measurements, 1 share each on **four** channels | 35.69 ms | 2.6 % | 4.58 ms |
+
+  So a pane is priced per measured **channel** (one `MeasureWindowReader`, one fetch, one scan)
+  and per **distinct share** (one accumulator), and the window's samples are the multiplier on
+  both: the same pane over a 2 M-sample window is the 1.2--1.6 ms a recompute this pane's
+  budget was fixed at, and a machine's ten noisy channels at a 15 s window is **tens of ms a
+  pass**, several times a second. That lands on the **tick** -- `update_measures()` runs inside
+  it -- so `frame cost:`'s tick mean is where a pane's cost shows (1.34 -> 4.58 ms above), and
+  it is *not* an ingest problem: `gaps=`/`packets=` stay exactly clean even though each
+  `MeasureWindowReader` holds `model->mutex()` for its whole life, because a socket buffer
+  absorbs a few tens of ms of producer. Read the tick mean and `each` before blaming the
+  producer.
+  Inside a pass the terms are, instrumented per window at that scale: the **fetch** 3.3 ms
+  (three out-of-line `MinMaxPyramid` accessors and a 48-byte `MeasureBucket` per bucket),
+  `measure_scan_buckets()` 0.8 ms, and **pass two** 7.5 ms -- dominated by the per-(bucket,
+  level) fold. That fold is why `measure_accumulate_bucket()` is `inline` in `measure.hpp`: it
+  is the innermost loop of a walk whose iteration count is the window's buckets *times* the
+  pane's levels, and as an out-of-line call in its own translation unit it cost **30 % of the
+  pass** (sixteen shares on one channel: `24.55 -> 17.25 ms` a recompute). A caller adding a
+  per-bucket type keeps it in the header, and a caller adding a bulk one may not let it grow a
+  call per bucket either.
+  The third term is `raw`, and it is the **signal's**: a level that falls inside a bucket's
+  `[lo, hi]` has to be walked sample by sample (the fold cannot split a bucket), so a signal
+  whose local range covers the level everywhere -- white noise, a noisy machine channel --
+  degrades the pass to O(window) *per level*: measured `raw=4.6 %` on the mock's `noise` channel
+  against `0.1 %` on its `sine` at the same window. It is the field to read before blaming the
+  pane for a slow run, and no cheaper walk fixes it.
+- **`Top`/`Bottom`/`Amplitude` read a *flat* level, and the density that finds it is the buckets',
+  not the samples'.** A band-limited edge overshoots and rings -- the mock's `square` at 30
+  harmonics reaches ±1.179 where its plateau is ±1 -- so a measurement that reads the extremes, or
+  a mean over a side of a level, reports the ringing rather than the level the signal dwells at:
+  that is what made this change (`amplitude` read `1.179350` and `top` `0.986496` on the rippled
+  square, against `1.179350` of overshoot where the plateau is `1`). A flat level is a *density*
+  question: the plateau holds most of the samples and the ringing a few percent. So
+  `measure_scan_buckets()` folds a 64-bin histogram of the whole buckets' *midpoints* while it has
+  the list in hand -- one observation per bucket, each bin carrying its buckets' **exact** sum and
+  finite count -- and `measure_flat_levels()` takes, either side of the split, the densest bin that
+  holds at least half the densest one's buckets, **the outermost of those**, and the exact mean of
+  the samples of the buckets within **5 % of the window's peak-to-peak** of it. 5 % is *under* the
+  ~9 %-of-swing Gibbs overshoot, so the ringing's excursion falls outside the band while a
+  plateau's own ripple stays inside it; the outermost-of-the-equally-dense rule is what makes a
+  waveform with *no* plateau -- a sine, a ramp -- read its peak instead of an arbitrary mid-range
+  bin that a shifted window would move. `Amplitude` is then `top - bottom`, a bench scope's
+  `Vamplitude`, and **not** the half-swing it used to be, nor the peak-to-peak swing.
+  The readings, fast mock, 2 s window, `[measure-trace]`, harmonics `0` → `30`: `top` `1.000000` →
+  `0.999983`, `bottom` `-1.000000` → `-0.999983`, `amplitude` `2.000000` → `1.999966`, against
+  `peak to peak` `2.000000` → `2.358701` -- the extremes keep the overshoot, and that separation
+  *is* the measurement. On the probe's 1 Hz ±1 sine: `top` `0.957988` (it was `0.636620`, the
+  half-wave mean), `amplitude` `1.915983`, and `peak to peak` still **exactly `2`**; `[stats-probe]`
+  reads `top` `mean=0.957905 sd=0.0014 lo=0.951967 hi=0.962348` over a scrolling window, which is
+  the stability the value band buys -- the answer does not follow the window's alignment.
+  Five things this rests on, each of which breaks something silently:
+  * **Nothing may be read raw for it.** The histogram is the *same* fetched bucket list, walked a
+    second time inside `measure_scan_buckets()`; a histogram of the window's *samples* would be a
+    second O(window) walk, which is exactly what the pyramid path exists to avoid. `measure cost:`
+    is the guard and its `raw` does not move: the probe's pane reads
+    `covered=59684972 buckets=932446 raw=47640 (0.1%)` against the baseline's
+    `covered=61183221 buckets=955856 raw=47402 (0.1%)` -- the same `raw`, 0.44 → 0.50 ms a pass
+    (and `--noise 0.1`, `2.1%` both sides, 0.52 → 0.65 ms).
+  * **It is gated, and the gate is what keeps an unrelated pane free.** `measure_scan_buckets()`'s
+    `flat_hist` comes from `App::MeasureWindow::flat_wanted`, set by the first loop over the pane
+    and only for one of the three types. A pane of means and extremes pays nothing.
+  * **The bin range is the *buckets'*, not the window's.** The window's partial edge buckets and the
+    samples produced since `acquire_all()` are read raw and are not in the list, so
+    `measure_scan_buckets()` tracks its own `blo`/`bhi` over the **non-empty** buckets only -- an
+    all-non-finite bucket is an empty aggregate whose `lo`/`hi` say nothing, and taking them would
+    put a bucket at some arbitrary value. A degenerate range (`bhi == blo`) leaves `folded` at 0,
+    which is the caller's "no histogram at all".
+  * **The *window's* peak-to-peak is what the band is a share of**, and the *split* is sized exactly
+    as `measure_set_level()` sizes a level, so "the top" and "the level a period is counted about"
+    are placed by one rule. The band is a *value* band, which is why the reading does not move when
+    the window does.
+  * **The fallback is the split, and it is what a filtered or sub-bucket window reads.** `hf_fc > 0`
+    disables the pyramid (above) and a window shorter than a bucket has no bucket to fold, so
+    `top`/`bottom` fall back to the mean of each side of the split -- and `amplitude` to the
+    window's own peak to peak, which is the same number on a waveform with nothing to exclude.
+    There is no flat level in that mode to subtract, so `amplitude == top - bottom` is *not* an
+    invariant to lean on there. Measured on the rippled `square` at `hf_fc=100`:
+    `top=0.973824 bottom=-0.991731 amplitude=2.354173 peak to peak=2.354173`, `buckets=0
+    raw=200.0%` -- two raw walks and no density estimate, which is the honest reading of a window
+    the pyramid cannot summarize.
+- **`Above`/`Below`/`Between` are the *means over a side of a share*, and they are the readings
+  `Top`/`Bottom` gave before a flat level replaced them.** That change kept the split's two means as
+  its *internal fallback* for a window the pyramid cannot summarize (above); these three types are
+  that fallback, exposed and named, which is what lets the two different questions about one split be
+  asked side by side -- on a unit sine `above 50` reads `0.636620` (2/pi) where `top` reads
+  `0.957988`, and on the mock's band-limited square `above 50` reads `0.986496` where the plateau is
+  `1.000000` and `top` `0.999983`: the edge's ring is *inside* this mean and not inside that level.
+  Five rules, and the first two are what a reader is most likely to assume wrongly:
+  * **A band is not a wider split, and needs no walk of its own.** `Above`/`Below` are
+    `MeasureLevel::sum[1]`/`count[1]` and `sum[0]`/`count[0]` at the measurement's own share.
+    `Between` is the **difference of two levels' upper sides** -- `sum[1](lo) - sum[1](hi)` over
+    `count[1](lo) - count[1](hi)`, i.e. the samples above the lower edge and *not* above the upper
+    one -- and no single level's two sums can bound a band, because a band's two edges are two
+    thresholds. Both accumulators come out of one pass two over one window (the pane registers one
+    level per edge, `w.pct`, and both are deduplicated into it), so the difference is exact rather
+    than approximate. `v == level` is the below side, as everywhere, so the band is `(lo, hi]`.
+  * **It rides the bucket fast path unchanged.** A bucket wholly inside the band is strictly above
+    the lower level *and* strictly below the upper one, so both accumulators fold it whole; only the
+    buckets that straddle either edge are opened, exactly as for one level. `measure cost:` is the
+    guard: adding all three types to a pane of every type left `raw` at `0.1%` of `covered`
+    (`113966` of `240719031` with the ten types, `134978` of `255372033` with the thirteen), and a
+    band is *two entries of the level list*, not a second pass.
+  * **`measure_level_pcts()` is the only place the shares are read**, and it clamps both to `[0,100]`
+    and puts `Between`'s pair **in order**: "between 80 % and 20 %" is the band between 20 % and
+    80 %. Normalized rather than refused because the shares name two *edges*, and the band does not
+    depend on which the user typed first; the pane's dedup key and both accumulators are keyed on the
+    ordered pair, so one band is one walk however it was written.
+  * **Nothing to measure reads `--`**, exactly as for every other type: a side holding no sample (a
+    share at `100 %`, whose level is the window's own maximum) and an *interior* holding none are
+    both `invalid`/`--` and never `0`. The ideal `--square-harmonics 0` square is where the second
+    shows -- every sample is exactly +/-1, so the band `(0, 0.5]` holds nothing -- against the same
+    band on the band-limited square, which holds the edges' transitions (`between 50 75` =
+    `0.302744`, `between 25 75` = `0.000000`: the symmetric band's two halves cancel, the transition
+    being odd about its own midpoint).
+  * **The reading is a mean over the window's *samples*, so its sixth decimal follows the window's
+    boundary.** A live window is closed at both ends, so its oldest and newest sample share a phase
+    and the mean carries one sample that is not in an open interval -- about one unit in the sixth
+    decimal out of 2.6 M samples. Measured over one fast-mock run, `[measure-trace]`: `above 50` on
+    the sine printed `0.636620` on 48 lines and `0.636621` on 2, `below 50` `-0.636620` on 37 and
+    `-0.636619` on 18, `above 50` on the square `0.986496` on 32 and `0.986495` on 18, and
+    `between 50 75` on the ramp `0.250000`/`0.250001`/`0.249999`. The old `Top`/`Bottom` spread the
+    same way -- it is a property of a mean over a finite window, not of these types, and a reading
+    that has to be exact to six figures is read off `[bandavg-probe]`'s nine.
+  Measured on the fast mock, 2 s window, the mock's default 30-harmonic square, `[bandavg-probe]`
+  (nine significant digits, then what the pane prints):
+  `above 50` on the sine `0.636620262` -> `636.62 mV`; `below 50` on the sine `-0.636619283`;
+  `between 50 75` on the sine `0.255873597` -- the analytic `3(2-sqrt 3)/pi = 0.255873`, which is
+  neither the window's mean (`0`) nor the band's edge (`0.5`); `above 50` on the square
+  `0.986494746` / `0.986495505` (one or two samples at the window's end); `between 50 75` on the
+  `ramp` `0.250000385` and `above 50` `0.500000` -- a uniform density makes every band's mean that
+  band's own centre, so a quarter and a half of the range are the shape's prediction and not a
+  coincidence; `above 100` on the `ramp` `--`; and the ideal square's `between 50 75` `--`.
+  Editing the sine's band through the dialog to `50/90` takes it to `0.431361697`
+  (`0.8 / (2 asin 0.8)`), which is the check that the second share is the one the engine reads.
 - **`MeasureOptions::noise_pct` is a percentage, clamped in `measure_set_level()` to half the room to the
   nearer extreme**, so a band can never invert its own thresholds. It moves the **edge decision only**: the
-  sums still split at the bare level, because `Top` on a unit sine must read 2/pi (0.636620).
+  sums still split at the bare level, which is the *fallback* `Top`/`Bottom` read on a window with no
+  bucket histogram -- a band that moved that split would change what a filtered or sub-bucket window
+  reports, for no gain to a crossing count.
 - **`measure_accumulate` loops samples outer, levels inner, and that is not backwards.** The filter holds one
   state for the whole walk, so levels-outer would step it once per level *per sample* and hand every level but
   the last a different filter state.
@@ -105,9 +298,13 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
     decides that side and the measurement reads nothing at all, which is worse than reading
     something noisy. On a ringing 3.3 V logic signal at a 90 % split: `enters=0` with a fixed band,
     `enters=4 period=0.200000` with the clamp.
-  * **The `sum`/`count` split stays at the bare `level`.** That split *is* `Top`/`Bottom` -- the mean
-    above and below the threshold -- so a band there changes a documented exact reading. `top` on a
-    unit sine must still be `0.636620`.
+  * **The `sum`/`count` split stays at the bare `level`.** Four things read it and none may be
+    moved by a band: a crossing's *side* is decided by the sample's own value against the level
+    (`v == level` is the below side, as it always was), `Top`/`Bottom` fall back to the mean of
+    each side on a window with no bucket histogram, and `Above`/`Below`/`Between` read it on
+    *every* window -- their whole definition is that split, so a band folded into it would move a
+    documented exact reading (2/pi on a sine) for no gain to any crossing count. The band is about
+    *deciding a crossing*, not about where a sample lives.
   * **`h = 0` must reduce exactly to the single-level walk**, including the `v == level` skip, so the
     band is a parameter of the engine rather than a mode of it.
   The cost is the noise's, not the band's: the clean fast mock reads `raw=119412 (0.1%)` of 215 M at
@@ -133,6 +330,10 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   changed".** An explicit Reset, an add/edit/delete (all three funnel through
   `rebuild_measures_pane()`), a CONFIG, and a change of display window each change the
   *question*, so the history is cleared. A pause, a resume, a trigger latch, a pan and a zoom do
-  not: they change which samples answer it, which is precisely what averaging over many windows
-  is for. The pane-wide toggle does not reset either — it only shows and hides labels that are
-  always created and always fed, so reading the plot for a moment does not cost the history.
+  not: on a **live** view they change which samples answer it, which is precisely what averaging
+  over many windows is for -- and on a **pinned** one they change *nothing*, not even a value
+  (the window invariant above), so there is nothing for the history to see either way. The rule
+  is about the *accumulator* only; it is not a claim that a gesture leaves a value alone, which is
+  a property of the window a value is computed over and is the other half of this change. The
+  pane-wide toggle does not reset either — it only shows and hides labels that are always created
+  and always fed, so reading the plot for a moment does not cost the history.

docs/claude/invariants-plot-and-layout.md

@@ -1,6 +1,6 @@
 # Invariants: the plot, the figure and the layout
 
-How `plot::Figure`/`plot::Plot` may and may not be driven, what a row's state belongs to, the layout editor's overlay, and the rule that layout must not depend on content.
+How `plot::Figure`/`plot::Plot` may and may not be driven, what a row's state belongs to, the layout editor's and the slide-over's overlay children, and the rule that layout must not depend on content.
 
 Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to learn; read the ones touching the area you are editing before you edit it.
 
@@ -12,9 +12,9 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   from the paned's own width, re-parenting the column, the property form of its children, size requests):
   the *mechanism* was the fault. It is an **`AdwOverlaySplitView`** now — what a utility sidebar is in
   GNOME, as against `AdwNavigationSplitView`, which is for navigation lists — with `min-sidebar-width` =
-  `max-sidebar-width` = 320 in **pixels**, so the width is its own at any window size, and `collapsed` (set
+  `max-sidebar-width` = 280 in **pixels**, so the width is its own at any window size, and `collapsed` (set
   from the window's width in `tick()`) to *overlay* the plot when there is no room beside it rather than
-  being squeezed. `[sidebar-probe]` reads both states: `window=756 sidebar=320` under a 2x scale is exactly
+  being squeezed. `[sidebar-probe]` reads both states: `window=756 sidebar=280` under a 2x scale is exactly
   the case that used to be zero.
 - **The sidebar's button is the only input; `AdwOverlaySplitView:show-sidebar` is an output.** The split
   view writes that property *itself* — at startup, and when it collapses — with no user involved, so reading
@@ -23,12 +23,13 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   toggle is the same mistake in one line, and it cannot be told from a real change by a "is this our own
   write" flag either, since the toggle's signal may fire after the write returns. Instead `App::sidebar_wanted`
   holds the wish (written only by `on_sidebar_toggled`, guarded by `App::sidebar_syncing` around our own
-  `set_active`), `update_side_visibility()` is the single place that turns that wish plus "are there signals"
-  into the panel's *and* the button's state together, and `tick()` re-asserts them when the widget disagrees —
+  `set_active`), `update_side_visibility()` is the single place that turns that wish into the panel's visibility
+  and "are there signals" into the dock's *sensitivity* (the button stays sensitive), and `tick()` re-asserts both when the widget disagrees —
   which is also why a hide *gesture* does not stick: the panel stays where the button says it is. The
   no-signals case must leave the wish alone, or a source connecting later finds a sidebar the user never closed.
+  The wish is the session's `dock` key: a change of it (not a program's own write, and not a restore) schedules a save.
 - **`AdwOverlaySplitView:sidebar-width-fraction` is a 0..1 fraction of the window, whatever
-  `sidebar-width-unit` says.** Setting a pixel count there (320) is a `GObject` critical, and it silently
+  `sidebar-width-unit` says.** Setting a pixel count there (280) is a `GObject` critical, and it silently
   falls back to 0.25 — which reads as "the sidebar is mysteriously 560 px wide" on a wide window with no
   error anywhere the build would catch. Pin the width with `min-sidebar-width`/`max-sidebar-width`.
 - **A `GtkPaned`'s position is stated after both its sides are filled**, and that is a fact about the
@@ -39,11 +40,19 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   moved the plot column by about 180 px, which the layout probe read as a different `done_box` and a
   taller figure.
 
+- **Events never take the plot's width.** The events list is a slide-over page (an overlay child over the plot) and
+  the dock's Events block lives in the fixed 280 px column, so there is no events divider, revealer or pane beside the
+  plot to squeeze it; the first latch must not move the plot area (`[events] ... plot_w_stable=1`, which compares the
+  allocated width before and after). A dock row is a fixed-width ellipsized label (title at 18 characters, `#seq`), the
+  list is a fixed 112 px scroller capped at `kDockEventsMax` rows plus one "N more" row, and it has no thumbnails: the
+  dock's width and height do not depend on how many events there are or what they say ("layout must not depend on
+  content"). The thumbnails are the *page's* (138 px wide).
+
 - **`plot::Plot` cannot remove or retarget a trace.** Hence fixed trace slots created
   up front and rebinding via `SlotSeries`; a *name* change (legend text) is the one
   thing that forces a rebuild. Cursors are parked outside the axis range instead of
   removed.
-- **A `Figure`'s row count is fixed at construction**, so `RowSet::rebuild_all()` builds
+- **A `Figure`'s shape (its cells per row) is fixed at construction**, so `RowSet::rebuild_all()` builds
   a *new* figure and the area is handed it (`PlotArea::set_figure()`); it costs no GL
   state. That makes one path for "a row's traces changed" and "the row count changed",
   and it is why `rebuild_all()` restates a pinned event window (`pinned_pre_`/
@@ -96,6 +105,153 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   an equal division. `sync_layout_editor()` runs every frame on purpose:
   `gtk_widget_set_margin_*()` returns early on an unchanged value, so a settled layout costs
   the comparisons and nothing else, and a resize needs no notification.
+- **A figure row can be split into cells, and every plot index in the host is the flattened one.**
+  `RowSet::row_count()` is the number of **plots** and `row(i)`, `Row::plot`, the cursors, the
+  measurements, `bind()`, the readouts and the persistence layers all index plots row-major (row 0's cells
+  left to right, then row 1's); `figure_row_count()` is the number of figure rows, and
+  `cells_in_row()`/`first_plot_of_row()`/`figure_row_of()`/`cell_of()` translate. **Code that means "the
+  rows of the figure" -- the editor's row `+`, the row drag, the row weights, `fl.rows` -- must say
+  `figure_row_count()`**: with no split the two are equal and a slip passes every unsplit probe, which
+  is how a row weight once drifted off its row (see the `row-weights` reading). The caps are
+  `kMaxCellsPerRow` = 4 per row and `kMaxRows` = 8 **plots** in all (the constant bounds plots now, not
+  figure rows), so every per-plot structure sized for 8 is unchanged. `plot_label()` is what the UI
+  prints for a plot: the row's number (`2`) for a one-cell row, the number and a letter (`2a`..`2d`) for
+  a split one -- never a flat index, which is 0-based and says nothing about where the plot is.
+  What the cells share and what each keeps:
+  - **One time window.** Every cell of every row is a member of the one x link group, so a pan or zoom
+    in any cell moves them all, the crosshair is one x drawn in every cell (the hovered cell shows its
+    y), and the **vertical cursor pair is one shared time drawn in every cell** (`cursors_aligned`).
+    A split is an arrangement of more plots, not a second time scale: nothing about the time axis changes
+    (see [invariants-time-axis-and-window.md](invariants-time-axis-and-window.md)).
+  - **One y per figure row.** The cells of a figure row share one y range (the plotter's
+    `Figure::set_share_row_y(true)`, which `rebuild_all()` sets before the cells are populated): one y
+    axis (auto or fixed), one pair of horizontal rulers, one fit. A wheel or axis drag in any cell moves
+    the row, an x gesture on any cell that carries an x strip moves the shared window. The host therefore acts on the
+    **figure row** of a plot it is given (`set_y_auto`, `set_y_range`, `fit_all`, the Auto/Fixed dialog,
+    `row_unit`, which joins the units of every cell and reads "" if they differ). The rulers are stored on
+    the row's first plot index, copied to the other cells by `sync_cursors()` / `insert_cell()` /
+    `rebuild_all()` and placed in every cell by `place_cursors()`. The cursors pane lists **one ruler line
+    per figure row**: `row N` with N the 1-based figure row for a split row, and the 0-based plot index
+    for an unsplit row (the pane read that before splitting existed). Readouts and measurements stay per
+    trace and per plot index; only the axis is shared.
+  - **The x axis is the bottom row's for every run of rows with the same columns.** A figure row gets
+    `XStrip::None` only if the row directly below has the same columns (same cell count and same
+    normalised cell weights); a row whose columns differ keeps its own strip under each of its cells
+    (`[1][2]/[3]` has axes on 1, 2 and 3), because the axis below is at another width and scale. The
+    rule is structural and transitive, never a function of content. Every cell that carries a strip is
+    a place a middle-drag on the axis works. The `t0` caption belongs on every cell that carries a strip,
+    not only the last figure row's.
+  - **The right gutter is the last cell's.** In a split row with a shared y the plotter gives
+    `right_gutter` to the last cell alone and takes it off the row like the y gutter, so the visible gap
+    between two plots is `col_gap` and equal weights give equal axes widths.
+  - **One left gutter, on the first cell only.** The y gutter is one maximum for the whole figure with the
+    same reserved floor as before (`Figure::set_min_y_gutter()`). It is carried by the first cell of each
+    row alone: `Figure::layout` gives every other cell `YStrip::None` from its column index (structurally,
+    never from what it holds), which forces its y label width, title width and reserved floor to 0. A
+    `None` cell contributes 0 to the common maximum, so a split row's non-first cells cannot widen the
+    gutter and a row's gutter does not depend on how many cells it has. A per-column gutter sized by the
+    labels would make a cell's width depend on its content, which "layout must not depend on content"
+    forbids. A row whose labels are narrower than the gutter simply has a wider margin. The weights apply
+    to **plot widths**, not cell rects (below).
+  - **Widths are weights with a floor.** The plotter keeps 64 px logical per plot and a column gap
+    (`kColGap`, 6 px); the editor's drag is stricter (below). The floors and the weights act on **plot widths**: the row's y gutter (carried by the first
+    cell) is taken off the row width first, then the cells share the rest, so equal weights give equal plot
+    areas and the first cell's rect is its gutter plus its plot width. A weight is a share of what is
+    left *after* the gutter and the floors, so cells of `{3, 1}` read 524:229 (rects) in a 756 px
+    figure, not 3:1, and the editor's 96 px drag floor is a floor on the plot *width*, not on the share. Because a cell's width is
+    `64 + extra * weight / total` and not proportional to its weight, `layout_col_apply()` does not scale
+    the pair's weights by the width ratio: it keeps the pair's weight sum `S` from the drag's *start*
+    (`layout_col_drag_start`) and gives the left cell `S * (want_left - 64) / (pair - 128)`, clamped to
+    `[0.001, 0.999]` (the plotter refuses non-positive weights; `0.5` if the pair is not wider than 128).
+    `want_left` and the pair are plot widths (`layout_col_drag_begin` reads each plot's `layout().axes.w`, after a `layout()` on the current figure, so the gutter and the inter-axes gap are never counted as weight); `want_left` is the pointer's width clamped to `[96, pair - 96]` logical px. The divider therefore
+    follows the pointer, the shrinking cell reads 96 px at the extreme and the pair keeps its total width
+    (the split probe's `col-drag` line asserts all three). `kPlotterMinCellPx` (64) mirrors the plotter's
+    `kMinCellWidthLogical`; both are logical px (the plotter scales it by `ui_scale`, which is
+    `PlotArea::device_scale()`, the divisor used to turn layout rects into logical px), so the two
+    must change together.
+  - **A cell is removed with its traces, and a new cell is empty.** `insert_cell(fr, at)` pushes the
+    cells at and after `at` right *with their contents* (the same rule as `insert_row()`), and
+    `remove_cell(plot)` on a one-cell row removes the row. Both return false at a cap or when they would
+    leave no plot, and never grow past 4 / 8.
+  **The editor's controls** (`rebuild_layout_editor()`): a cell `+` (`kLayoutCellKey`, tooltip "split
+  here") at a row's left edge, at its right edge and at every internal boundary -- `n + 1` of them for a
+  row of `n` cells, so a one-cell row can be split from either side -- inserting at that position; a drag
+  double-headed arrow (`kLayoutColKey`, `udpscope-resize-cols-symbolic`) at each internal boundary that moves the boundary between
+  its two neighbours, **each floored at `kMinCellPx` = 96 px logical** (or half the pair when the pair is
+  narrower) and measured from the two widths at drag start, so the drag does not compound. **The handle follows the divider it
+  drags, so the gesture's offset shrinks by the handle's own displacement**: `on_layout_col_update` adds it back
+  (`layout_col_total_offset(offset, handle_x_now, handle_x_at_begin)`, the handle's x in overlay coordinates, stored by
+  `on_layout_col_begin` in `layout_col_drag_handle_x0`) before multiplying by the scale; without it the divider settles at half the pointer's travel. The per-plot
+  `×`, which removes the cell in a split row ("remove this plot") and the row in a one-cell row ("remove
+  this row"), insensitive when it would leave no plot. Cell `+` is insensitive at 4 cells in its row or 8
+  plots in all; the row `+` is insensitive at 8 plots. **The cell `+` is keyed by `kLayoutCellKey` (figure row * 8 + position + 1) and
+  never by `set_row_key()`**: `row_key()` is a plot or boundary index, `layout_button()` finds a button by it,
+  and a cell `+` that also carried one would be found as a row button; `sync_layout_editor()` tells the kinds
+  apart by which key it finds. Like every editor control the
+  cell buttons are placed from `FigureLayout::cells`, divided by `device_scale()`, and the editor does
+  not draw while the figure's rects are not yet one per plot.
+- **The slide-over is the second thing placed over the plot, and it is one opaque widget, not a
+  transparent area.** The same pick rule as the editor's buttons applies, harder: the panel is a
+  `GtkRevealer` aligned to the end edge (`halign=END`, `valign=FILL`) at `kSlideOverWidth` = 360 px, so
+  its allocation *is* the part of the plot it covers and everything to its left is still the plot's --
+  pan, zoom, drop and hover are untouched. A full-area child with a panel drawn in it would swallow all
+  of them. Closed, the revealer is `can_target(FALSE)` (and `gtk_overlay_set_clip_overlay()` keeps its
+  slide-out inside the plot), so the frames of a slide-out do not eat input either. `[slideover]` reads
+  it back: `outside_hits_plot=1 inside_hits_panel=1`. Three consequences:
+  the panel **never resizes the plot** (it is an overlay child; `plot_unchanged=1`), its height is the
+  plot's and never the page's (each page has a `GtkScrolledWindow` with a `NEVER` horizontal policy that
+  does not propagate its child's height), and content that is taller than the plot -- the trigger form
+  on a 470 px window -- scrolls inside the panel instead of growing it. The widgets that go in a page
+  are reparented into it; their widths must fit 360 minus the border (the trigger form measures 267
+  minimum, the E-1608's panels 197). **One page wider than that widens the panel
+  for all of them** (the stack measures every page): the signals page's hint line once did, unwrapped, and
+  `[slideover] panel=` read 376 instead of 360; the label now wraps.
+- **The badge bar has a fixed height and sits outside the overlay.** `badge_bar` is 36 px
+  (`height-request`) between `plot_overlay` and the status line, so the plot above it never moves when a
+  badge's text changes (`bar_h` = `bar_h_after` in `[badges]`). This is "layout must not depend on
+  content" for the new row: the Trigger badge's state is a word from a short fixed set and the Source badge
+  (shown only when the kind has source pages; hidden otherwise) is a kind's display name only (no connection state: that is the status bar's), so what changes with the stream is the row's *width* (the bar has room to
+  spare on the right) and never its height. The badge labels are not ellipsized: a name long enough to
+  need it would be a defect of the kind's `display_name()`. Rows that appear by trigger condition appear
+  inside the slide-over's scroller, never in the bar.
+- **The signal badges live in a scroller, so the bar's minimum width never depends on the signal count.**
+  The bar's signals slot holds a `GtkScrolledWindow` (horizontal `EXTERNAL`, vertical `NEVER`) around one
+  row of badges and the `+`, because a button row's minimum width is the sum of its children: nine badges
+  (the E-1608: eight inputs and the counter) would push the window's minimum width past a laptop screen.
+  Past `kMaxSignalBadges` (6) the row is replaced by one "N signals" badge, which also stands for the `+`.
+  The bar's height stays 36 px in every one of these states (`bar_h_fixed` in `[sigbadges]`), and
+  `bar_min_w` reads the same with one signal, nine signals and the overflow (244 on the E-1608, 124 on UDPS:
+  the Source badge is on screen for the E-1608 and hidden for UDPS, and its text differs by kind). A change that makes it grow with the signal count has
+  taken the scroller out of the measurement.
+- **The dock's width is fixed too, and it is the readouts' width that holds it there** (`side_column`
+  `width-request` 260, the split view's 280 px floor and cap). The dock holds only the compact readouts and the Events block (a fixed-height list, below), so a
+  section's visibility is never what makes it taller; the scroller absorbs the rest. **The readouts' minimum
+  width is the sum of their cells' character widths, and it must stay under 280** (the Readouts box is 268:
+  280 less its 6 px margins): a cursor line is the `who` cell (5 characters) plus three value cells (9 each),
+  every one ellipsized at that width (`width-chars` = `max-width-chars`), so a long value is cut and its
+  tooltip carries the text and the layout never depends on what a value reads. The `who` cell was 8
+  characters, which made the readouts' minimum width 304 px; that pushed the sidebar to 304 px
+  (`dock_w=304`) and defeated the 280 pin. Widening any cell is the same
+  trap -- read `[readouts] ... dock_w=` (must be 280) and the `dock cursors:` / `dock measures:` `fits=`, and for the Events block `dock events: ... dock_w=` (268).
+- **The readouts strip is a fixed 26 px, scrolls sideways, and is shown only when the dock is not beside the plot and there is something to read.**
+  `readouts_strip` (a `GtkScrolledWindow`, `height-request` 26, horizontal `external`, vertical `never`) sits
+  in `left_column` between `plot_overlay` and `badge_bar`. Its height is a request and not a measurement of
+  its chips (the buttons are trimmed by `button.udpscope-strip-button` in `ui_widgets.cpp`, or Adwaita's
+  34 px flat button would push it past 26), the chips' cells are fixed-width ellipsized labels like the
+  dock's, and an overflow scrolls with no bar taking height: "layout must not depend on content" for the
+  strip, the same as for the badge bar. It is *visible* exactly when (`show-sidebar` is false **or** the split view is `collapsed`)
+  **and** (the cursors are on **or** there is a measurement)
+  (`sync_readouts_strip()`, from the tick after the wish is re-asserted and before `set_collapsed()` -- so
+  `show-sidebar` is the wish and not the split view's collapse-time write, and `collapsed` is the previous
+  frame's value). Hidden with a wide window and the dock beside the plot, so the plot's 26 px go to one
+  pane of readouts and never both, and hidden with nothing to read (cursors off, no measurement). That last
+  is a deliberate, user-requested exception to "disable, do not hide": an empty strip is 26 px of nothing, and
+  the dock keeps both blocks on screen so the empty state is never invisible; the strip's two groups and the
+  separator follow the same rule (`strip_cursor_group` with the cursors, `strip_measure_group` with
+  measurements, `strip_sep` with both). In a collapsed window the dock is an overlay on the plot and the strip
+  stays, overlay open or not. The plot is 26 px shorter while it shows; that is the dock's and the window's
+  state moving the layout, not content. Reading `h=26` with `visible=1` (and `h=0` with `visible=0`) in
+  `strip:` is the assertion, `visible_ok=1` that `visible` equals `expected` and `groups_ok=1` that the groups agree.
 - **Trace slots are identified by signal name, not channel index.** Enabling a signal
   or a new CONFIG renumbers the channel list, so an index would silently re-point a
   trace at another signal.
@@ -118,6 +274,8 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   per-channel list, and why `format_elapsed()` steps to a coarser unit instead of
   letting the counter grow: each is a status field whose *width* would otherwise depend
   on the stream, and the status row is directly above the plot.
+  A split row keeps this rule: cell widths come from the weights and the 64 px floor and never from what
+  a cell's labels need, and the gutter stays one figure-wide maximum.
   The reservation goes on the **figure** (`Figure::set_min_y_gutter()`, added to the
   plotter for this), not on the rows: `Figure::layout()` clears every row's
   `set_min_y_gutter()` to measure what its own labels need, so a floor written onto the

docs/claude/invariants-readouts-and-cursors.md

@@ -41,6 +41,38 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   window's **first sample** and never from history before the window, so a measurement never depends on data
   outside the window it reports on: the left-edge step transient is removed by the seeding, not by priming
   from earlier samples.
+- **The dock's readouts and the pages' panels are one string, never two.** The dock (`src/ui_dock.cpp`)
+  shows a read-only copy of the cursors table and of the measurement values, and it must not format
+  anything: `update_cursors_pane()` and `update_measures()` format each value **once**, into a local, and
+  hand that same variable to the page's label **and** to `dock_cursor_cell()` / `dock_measure_value()` --
+  on every branch, including the `"--"` blanking one (cursors off, no sample). A second formatter in the
+  dock would be two spellings of one reading that drift the first time `format_measure()` changes, and
+  the dock exists so that the two can be read side by side. The `who` cell is copied from the page's label
+  verbatim (markup chip and name), and the dock's lines are rebuilt from the page's whenever the page
+  rebuilds (`dock_rebuild_cursors()`, `dock_rebuild_measures()`), so the line counts agree by
+  construction. A cell is **ellipsized at a fixed character count** (who 5, values 9, measurement type 12) with
+  the full text in its tooltip: the dock is 280 px wide and its layout must not depend on what a value
+  reads, so a long value is cut and quoted whole in the tooltip rather than widening the column (the
+  `who` cell was 8 characters, which made the readouts 304 px wide and pushed the sidebar past its
+  pin). `[cursors-probe] ... dock cursors:` and `[measures-probe] ... dock measures:` assert it: `same_text=1`
+  compares `gtk_label_get_text()` (the untruncated text) of every dock label with the page's, and
+  `fits=1` that the Readouts box is no wider than the dock.
+- **The readouts strip is a third reader of the same string, never a second formatter.** When the dock is
+  not beside the plot (hidden, or the window collapsed so the dock is an overlay) the readouts are shown in the strip under the plot (`readouts_strip`, `src/ui_dock.cpp`): the
+  cursor chips' `who` and *delta* labels and the measurement chips' value labels. They are written **in the
+  same call** as the dock's -- `dock_cursor_cell()` and `dock_measure_value()` set the strip's label from the
+  argument they were handed, and `dock_rebuild_cursors()` / `dock_rebuild_measures()` rebuild its chips
+  beside the dock's lines -- so a value is still formatted once, into one local, and a feature that writes a
+  dock cell without going through those two setters leaves the strip stale. The strip keeps the dock's
+  rules: the same fixed-width ellipsized cells (who 6, type 10, value 9 characters, full text in the
+  tooltip), the delta cell reads `--` on the same branches, and the cursor chips are *insensitive* with the
+  cursors off -- through `dock_set_cursors_sensitive()`, which writes the dock's grid and the
+  strip's chip box together; a second `gtk_widget_set_sensitive()` on either is two spellings of one state.
+  The one place the strip hides what the dock only disables: with the cursors off the strip's Cursors group is
+  not shown, with no measurement its Measures group is not, and with neither the strip is not (the dock keeps
+  both blocks, `no measurements` included; the strip has no placeholder). That is
+  `sync_readouts_strip()`, not a sensitivity.
+  `[cursors-probe]` / `[measures-probe]` `strip: ... same_text=1` asserts it.
 - **`format_measure()` is the one formatter for both panes, and its SI prefix does not depend on
   there being a unit.** The cursors pane's values and the measurements pane's `text=` go through
   it, so a change reaches both. The prefix ladder used to be inside `if (!unit.empty())`, which
@@ -54,6 +86,12 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   unit and a spaced `m` alone reads as metres; with one it stays spaced and the prefix joins the
   unit (`636.62 mV`). Below `1e-12` the ladder runs out, and `%.2f` would print `0.00` again, so
   that range falls back to `%.3g`.
+- **With the instruments off the readout blanks, and the panel stays on screen.** Cursors-off makes the
+  pane *insensitive* (the page's body, and the dock's cursor grid beside it) rather than hiding it -- a panel you can still see is a panel you can read, and the
+  settings you are about to switch back on must not vanish while you look for them -- and every cell in
+  it is written `"--"`, the spelling an unavailable cell already uses. A readout quotes a stored sample;
+  with nothing bracketing one there is no sample to quote, and keeping the last values would be quoting
+  a sample the cursors no longer name. Two spellings of one state in one grid would be the defect.
 - **The cursors are read back from the plots only while a gesture is on that row.** `Cursor::x`
   is the *free* pointer position while a drag runs and the snapped value otherwise -- which is
   what the app itself wrote a frame earlier, or the snap of it. A tick that reads a row on

docs/claude/invariants-session-and-export.md

@@ -4,14 +4,42 @@ What a session persists and in what order, when a save is refused, and when an e
 
 Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to learn; read the ones touching the area you are editing before you edit it.
 
+- **The trigger is persisted, settings and state both.** Its condition, its channel (by *name*), its
+  pre-trigger share, hold-off and mode, and whether trigger mode was on — written even while it is off,
+  because a trigger configured once and switched off is still the trigger you come back to. The two
+  enumerations are stored as the *words the panel's dropdowns show*, not as their indexes: an index ties
+  the file to a declaration order, which is the lesson `math_op_at()` carries, and the words are shared
+  with the panel so the two cannot drift. The channel resolves when the acquired channels exist
+  (`rebuild_trigger_signals()` picks up `App::pending_trigger_channel`, or `apply_trigger_layout()`
+  resolves it itself when they are already there) — a name that resolved to nothing would silently move
+  the trigger to channel 0.
+- **A session that loaded is what locks the trigger pane.** Locked is the returning user's mode: the
+  trigger pane shows one compact line and offers no control that changes the configuration (the signals
+  have no lock). A *first run* — no session file for that source — never
+  reaches `apply_layout()` and stays in configuration mode, which is what a first run is for. The mode
+  is a mode and not a setting: it is deliberately not persisted, so a scope reopened tomorrow starts
+  where a returning user expects to start. **Dragging a signal onto a plot is not configuration and survives
+  the lock**: it is the signal *badge's* drag (the list's rows are no longer drag sources, and the badges do
+  not follow the lock). `[sigbadges] drag_sources` is the reading, and `drag_sources` on the `signals panel:`
+  line must be 0.
 - **The session is the layout.** `LayoutState` persists what makes a reopened scope look like the
-  one that was closed: the window, the rows and their slot signals, the calibration, **the enabled
+  one that was closed: the window, the rows and their slot signals, the calibration, **the unit renames**
+  (`[[unit]]`, `name` + `unit`, only the overrides; `ScopeModel::set_signal_unit` re-applies them to every CONFIG,
+  and `set_signals()` takes them off the incoming units before the "same stream" comparison so a reconnect still
+  keeps its history), **the enabled
   signals**, **the chosen trace colours** (`[[color]]`, `name` + `rgb = "#RRGGBB"` — only the
   *overrides*, so a stream's new signals still take the positional palette and a saved session does
   not freeze a colour that is meant to follow the signal list), **the math channels with their
   graphs**, **the measurements pane**, and **`measure_stats`** — the measurements statistics
   toggle; written as a bare top-level boolean (`measure_stats = true/false`), defaults to `false`
-  when absent. Signal identity
+  when absent, and **`dock`** -- `LayoutState::dock_shown`, the Dock button's state (the user's last word on it,
+  `App::sidebar_wanted`): a bare top-level boolean written where `side_tab` used to be, default `true`.
+  It is the **only** thing the dock persists -- its 280 px width is fixed, so there is nothing to store --
+  and **the open slide-over page is deliberately not persisted** (a panel that opens by itself at start-up
+  is a surprise, and a page id from another source kind may not exist). The parser ignores unknown keys
+  (its key chain has no erroring final `else`), so a file written before the tabs became a dock
+  (`side_tab = "measure"`, or `side_tab = "source-ao"`) still loads and opens with the dock shown;
+  nothing reads the old key, and `[dock-session]` asserts it. Signal identity
   is the *name* throughout (a CONFIG renumbers channels), 'enabled' is read off the channels the
   model built -- an enabled signal is exactly one that produced a channel -- and `apply_layout()`
   installs the graphs **before** assigning the rows, since a row may hold a math channel's name and
@@ -23,9 +51,35 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   was parsed into the last calibration record and the enable state was lost without a word.
   `mkdirs()` used to create only components with a trailing slash, so `~/.config/udpscope` was never
   made and the *first* save failed silently -- worth knowing when a layout change "does not stick".
-- **Measurement options persist under *named* keys -- `noise` and `hf` -- so a file written before them
-  loads at the defaults**, which are exactly the behaviour it was written against: `noise = 10` is the
-  hysteresis band the app has always counted with, and `hf = 0` is no filter.
+- **A `[[plot]]` table is one *plot* (one cell), and carries `row` and `width` for the horizontal split.**
+  `plots = N` counts plots, as it always did. `row` is the 0-based **figure row** the plot sits in and
+  `width` the cell's share of that row's width (`LayoutState::Row::row`, `::width`); the tables run in
+  the flattened order, so a row's cells are consecutive and left to right. The row's height share
+  `weight` stays per *figure row* but is **written on every cell of it** (so a table read alone is
+  complete) and **read from the row's first cell**; `collect_layout()` takes it from
+  `row_weights()[figure_row_of(plot)]`, not from `row_weights()[plot]` -- the latter is a plot index into
+  a figure-row vector, right until the first split. The file is written `row`, `width`, `weight`,
+  `signals`; a state built with `row < 0` (nothing in the app does) omits `row` and `width`.
+  Three loading rules, all in `apply_layout()` and none of them a refusal, because a session is the
+  user's arrangement and not worth losing to a malformed key:
+  (1) **a file with no `row` loads as one cell per row** -- every session written before the split --
+  with the per-plot `weight`s as the row heights, exactly as it opened before;
+  (2) **a `row` sequence that cannot be a layout loads the same way**: some plot without a `row`, a row
+  number that goes backwards or skips one, a first row that is not 0, more than 4 cells in a row, or
+  more than 8 plots; the signals stay on the plots they were on (`invalid-rows` is the reading);
+  (3) **cell widths are applied after the arrangement**, because `set_cells_per_row()` resets them, and
+  only for rows of two or more cells -- a one-cell row has no widths and its `width` is ignored.
+  Both new keys are parsed with the file's other forgiving rules: `row` must be an integer >= 0 and
+  `width` a number > 0, anything else leaves the default. A save after loading a pre-split file writes
+  the `row`/`width` keys, which is how an old session is upgraded without anyone asking.
+- **Measurement options persist under *named* keys -- `threshold`, `threshold2`, `noise` and `hf` -- so a
+  file written before them loads at the defaults**, which are exactly the behaviour it was written against:
+  `noise = 10` is the
+  hysteresis band the app has always counted with, `hf = 0` is no filter, and a file with no
+  `threshold2` -- every file written before `between` existed -- leaves that measurement at
+  `threshold2 = 75`, which is the value the dialog offers a new one. The *pair* is stored as written
+  rather than as ordered: `measure_level_pcts()` is what puts a reversed pair in order on read, so a
+  file records what the user typed and a measurement file round-trips unchanged.
 - **The math node string is thirteen pipe fields, and the reader accepts twelve *or* thirteen.** `med_n` is
   the thirteenth, after `y`; a twelve-field node is a file written before the de-noise node existed, and its
   `med_n` stays at the struct's default -- which is what such a file meant. Field 0 is the op as a
@@ -33,6 +87,40 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
 - **The export is collected at click time, not in the file-dialog callback.** The live
   view keeps scrolling while the chooser is up, so a late collection would write a
   window the user never saw. The writer is picked by the chosen path's extension.
+- **The MDF export is MDF 3.30 written by hand, and its layout is the reader's, not the
+  standard's prose.** No dependency is added: MF4 is HDF5 and would need a library, while MF3 is a
+  handful of fixed-size blocks, so `write_mdf()` spells them out. The field list comes from
+  `asammdf` 8.8.27 (`blocks/v2_v3_blocks.py`, `blocks/mdf_v3.py`, which parses MF3 by explicit
+  offsets) and was confirmed byte for byte against a known-good 3.30 file asammdf wrote (one
+  group, a `time` master and two `V` channels). The shape, in file order: the **ID block** is 64
+  bytes with *no id/length header* (`"MDF     3.30"`, byte order, version `330`) — a writer that
+  emits `ID` + size + links at offset 0 produces something no reader accepts, since the first real
+  block starts at 64; the **HD block** is 208 (164 common + 44 of the 3.2-era time fields) and
+  points at the data group; a **TX** comment follows it; then the **samples**; the **DG** is 28; a
+  **CC** (conversion, 46 — a `NONE` conversion is the common fields alone) then a **CN** (channel,
+  228) precede each channel; and the **CG** (30) is last. Address fields are absolute file offsets
+  written *forward*, so the whole address map is computed before a byte is written, and every
+  block length is checked after it is built: a field at the wrong width does not fail the write, it
+  leaves the reader in the middle of the next block.
+- **The data group's data address holds the raw records, with no `DT` header** — which is what
+  asammdf's *writer* does and what its *reader* assumes (`DataBlock` is documented as "a pseudo
+  block not defined by the MDF 3 standard"). This is the one place the file follows the reader
+  rather than a narrow reading of the standard, and it is the assumption ScryLab compatibility
+  rests on: a file with a `DT` block there would have its header read as sample bytes.
+- **In MDF the master is `abs_seconds`, named `time`, and the relative axis is a channel
+  `time_relative`** — the same two numbers the `.npy`/`.csv` table holds, in the other roles. A
+  master off the relative column is 0 at a different sample in each display mode, so it would put a
+  live export and a held event's export on two timelines, which is the one thing the second column
+  exists to avoid; both carry the unit `s`, and the signal columns follow in the `.npy`/`.csv`
+  order. **The unit** is the client's CONFIG unit (a math channel's own), and it is written into
+  the CC block because that is the only place MDF 3 keeps one — and the place ScryLab reads a
+  signal's unit from. `ExportTable::Column` gained the field for it; the two older writers ignore
+  it, and their bytes are unchanged. **The names** are sanitised and de-duplicated against each
+  other *and* against the two reserved names before being cut to 31 bytes (the CN name field is 32
+  with its NUL): ScryLab imports only the **first** occurrence of a channel name, so a cut made
+  before de-duplication could silently drop a signal. `write_export()` is the one place the
+  extension picks the writer (`.csv`, `.mf3`/`.mdf`, anything else `.npy`), and both the dialog and
+  the self-check's export probe come through it so the two cannot offer different formats.
 - **The chooser runs before `ScopeModel` exists, and `--server` is what decides.** `Config` carries
   `server_specified`, set only by the `--server` branch, and `main()` asks only when it is false —
   so declining costs no buffer and no socket, and `ScopeModel`, `Acquisition`, `RowSet` and
@@ -81,7 +169,7 @@ expression of the scheme, and the name is `sanitize()`d exactly as the host is,
 with a slash cannot escape the directory.
 
 A configuration carries the whole session *and* the settings that can only be decided before the
-first socket: `buffer_mb`, `relative_time`, `capture_packets`. The startup chooser applies them
+first socket: `buffer_samples`, `relative_time`, `capture_packets`. The startup chooser applies them
 (`apply_source()`), which works because `choose_source()` runs before `ScopeModel` is constructed
 — the one moment a buffer size can be applied at all. Switching configurations inside a running
 app applies what can change live and says in the status line that the rest takes effect on the
@@ -92,9 +180,9 @@ A configuration's *startup* settings reach the model from two directions, and bo
 named with `--server`, which never reaches the chooser at all. Without the second, a saved host's
 buffer size, clock and capture ring were silently ignored — the layout still applied, because the
 app loads that separately once a CONFIG names the signals — so an edit to any of the three read as
-one that never took effect. **A flag the user typed wins over the file** (`--buffer-mb`,
+one that never took effect. **A flag the user typed wins over the file** (`--buffer-samples`,
 `--relative-time`, `--capture-packets`): the file fills in what the command line did not say, and
-`Config::buffer_mb_specified` is what tells "not asked" from "asked for the default".
+`Config::buffer_samples_specified` is what tells "not asked" from "asked for the default".
 
 The `active` file is written on every save and by the chooser's pick, so "which configuration was
 I on" survives a restart. A session written before configurations existed is **imported once** as

docs/claude/invariants-time-axis-and-window.md

@@ -73,8 +73,9 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   crawled across the plot under a pan and drifted under a zoom, which is what "[t0=...s] move
   slightly around when user zoom/pan" was. Three things follow. The **text is the host's**, because
   the caption has to name the anchor precisely enough that label + caption is the exact absolute
-  time and `format_time()` would round it to three figures (`"t0 = %.6g s"`); only the **bottom
-  row** of the figure carries one, every other row being set to `""`; and the renderer measures it
+  time and `format_time()` would round it to three figures (`"t0 = %.6g s"`); only a plot
+  whose x strip draws labels (`plot::x_strip_has_labels(x_strip_mode())`: the bottom row, and any row above it whose
+  columns differ from the row below's) carries one, every other plot being set to `""`; and the renderer measures it
   rather than `Plot::layout()` — it reserves no space and nothing can be picked on it, so there is
   no rect to read back, and a caption explaining the x labels must not be able to move the layout
   those labels were measured into. The guards are the library's
@@ -86,7 +87,8 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   path a resume takes). Pinned — a held event, a filling capture or a paused view — it is the
   **pin's** full range, which is the snapshot's own stamps and may be legitimately *narrower*
   than the requested window. It must write the per-row **member** axes as well as the link group:
-  `hold_pinned_window()` prefers a member that differs from `pinned_stated_`, which is how it
+  `hold_pinned_window()` prefers a member that differs from `pinned_stated_` (it scans **every**
+  row's member, in order, since a labelled strip on a row other than the first takes x gestures too), which is how it
   tells a real gesture from its own echo, so writing the group alone is reverted to the zoomed
   range on the next frame. `fit_all()` is the y fit plus this, shared rather than duplicated so
   the two cannot drift apart.

docs/claude/invariants-trigger-and-pinning.md

@@ -18,8 +18,43 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   reports it as `zoom ... span=.. window=.. limited=1`.
   Its pan clamping is likewise gated on the data being wider than the view, or the empty
   left-hand side drags the live edge off the right-hand edge.
+- **The compact pane's arm control is built in the heading, and *one* function states both arm
+  buttons.** Arming is a runtime decision and the locked pane is exactly where it is made, so the
+  control cannot live in the body — that is the part which goes away. `sync_arm_buttons()` is what
+  states the label, the sensitivity and the visibility of both buttons, and it is called from the four
+  places any of its three inputs can change (the click, the toolbar toggle, the curator's re-read,
+  `apply_pane_lock()`). Visibility is `enabled && locked`: with trigger mode off the line beside it
+  already says "stream (trigger off)" and there is no engine to arm, and with the pane open the body's
+  button is the one on screen — **two arm buttons at once would be two controls for one state**, which
+  is why the probe reads the body's allocation as `-1` while the compact one is up.
+  **The same function states the Force button beside the arm one, and the Force button is in the body
+  only.** Its sensitivity is the same `enabled` (a trigger that is off has no engine to force) and it
+  is stated in `sync_arm_buttons()` for the same reason the pair above is stated there — one place, so
+  nothing can drift — but it is *not* armed-gated: in Single mode the previous acquisition leaves the
+  engine disarmed, which is exactly when a user reaches for Force again, so a button that greyed out
+  with the engine's armed state would be unavailable for the one thing it is for. It stays in the body
+  because the heading's single control is the runtime *state* a locked pane exists to change, while a
+  force is an action whose subject — the condition, the level, the pre/post split and the mode that
+  decides whether one acquisition is all of it — is in the body; a second Force in the heading would
+  be a second control for one action whose settings are off screen.
+- **A widget's allocation is not readable in the tick it is first shown.** The compact arm control is
+  created hidden and shown for the first time inside a signal handler, so `gtk_widget_get_width()` in
+  that same tick reads `0` while `gtk_widget_is_visible()` already says `1` — and its sibling's stale
+  allocation (270 px, from when the *body* was still on screen) reads as a live one, because
+  `gtk_widget_get_visible()` is the widget's *own* flag and stays true under a hidden parent. The width
+  only becomes the proof that a control is on the surface **one frame later**, which is why the probe
+  has a `compact_arm_step()` of its own; and the control to compare against must be measured with
+  `is_visible()` or not at all.
 - **Signals start disabled** — enabling is what starts acquisition. A trigger on a
-  signal nobody acquires can never fire, so selecting/arming enables it.
+  signal nobody acquires can never fire, so selecting/arming enables it. **And the signal is resolved
+  *through* the channel, never taken as one.** `TriggerConfig::channel` indexes `channels()` (the
+  acquired ones) while `ScopeModel::set_signal_enabled()` indexes the stream's `signals()`, and the
+  two are not the same index: with one signal acquired, channel 0 *is* that signal while signal 0 is
+  the stream's own clock. Passing one for the other switched on the time base, left the signal the
+  trigger watches exactly as it was — and, because a signal the panel was not showing *is* a change,
+  rebuilt the buffer under the click and dropped its history, which is precisely the pre-trigger
+  window an arming, and now a force, was about to capture. `trigger_signal_index()` is the one
+  resolution and both buttons go through it.
 - **The trigger's event window is separate from the display window**, and
   `pretrigger_pct` is a share of the *event* span, not of the ring.
 - **The event window is counted in stream seconds end to end; nothing converts it to
@@ -35,8 +70,15 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   `Acquisition::on_data()` on **every packet** out of `model_.trigger()`. `TriggerConfig::channel`
   is an index into `channels()`, and that index is not stable: every rebuild of the channel list
   renumbers it — enabling a signal that sorts before the trigger's own is enough — and
-  `ScopeModel::set_signal_enabled()` re-resolves the trigger by name and writes the *new* index
-  back. Keying the reset on the index therefore made any such rebuild abandon the capture **and
+  **`ScopeModel::rebuild_channels()` re-resolves the trigger by name and writes the *new* index
+  back, for every caller.** It lives there and not at the call sites because the function *is* the
+  renumbering, and a caller that forgot is a trigger that silently stops: the name-based restore
+  used to be in `rebuild_enabled_locked()` alone, so adding or removing a math channel went through
+  `set_math_channels()`'s structural path with no restore at all, `rebuild_locked()` clamped the
+  now-wrong index to `-1`, and `process()` returns at once on a channel of `-1` while the panel went
+  on naming the channel. That is the second half of the "it sometimes does not trigger, even with
+  the trigger on a non-math channel" report. Keying the reset on the index made any such rebuild
+  abandon the capture **and
   set no hold-off**, so the next edge inside the post window became t0: that is the "the trigger
   re-triggers during a capture and the hold-off does not apply" defect, and it needed no glitch
   and no user action beyond enabling a channel. The name changes when the source genuinely
@@ -57,13 +99,20 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   the far threshold of the side it is leaving. Seeding the previous side from `0` -- the undecided code --
   fires on a signal that starts *inside* the band and leaves it without ever reaching the level, an event the
   trigger is not supposed to see.
-- **A pinned window is *clamped* into the event every frame, and a zoom in is allowed.**
+  **A pinned window is *clamped* into the event every frame, and a zoom in is allowed.**
   While an event is held, a capture is filling, or the view is paused, `tick()` calls
   `RowSet::hold_pinned_window()`, which caps the span at `[-pinned_pre_, +pinned_post_]`'s and
   clamps the position into it (and states `Off`, since a following group would re-derive from a
   live edge). **A zoom in must keep working** -- "not outside the event" is not "not readable",
   and this function's first version *re-stated* the pin every frame, which made the wheel a no-op
   in single trigger mode: an acquired event could not be examined at all.
+  **What a gesture inside the pin may *not* move is a measurement**, and it is not this function
+  that holds that: `pinned_range()` is the one expression of the pin's extent, and
+  `update_measures()` measures *it* rather than the viewport while the view is pinned, so a pan
+  or a zoom on a still frame changes no value and spends no recompute (see
+  [invariants-measurements.md](invariants-measurements.md); `[measurepin-probe]` is the reading,
+  `pin=`/`for=` in `[measure-trace]` the field to watch). The pin is therefore load-bearing twice
+  over, and a change to what `pinned_range()` says changes both the framing and the numbers.
   **The request is read from the row's own axis, not from the group.** A member's `set_x_range`
   -- what the controller writes for a gesture -- is *not* adopted into the group while the follow
   is off, so a clamp that read the group only ever saw its own previous answer (the probe showed
@@ -124,6 +173,18 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   afterwards if the probe zoomed in. Before the fix the two disagreed outright:
   `axis=[-1.44..0.56]` over data that started at `0.0`. (The event pin already worked this way; the
   pause now agrees.)
+- **The pause reads the display offset *before* it sets the pause state, and a pause taken on a
+  held event depends on that order.** `on_pause_toggled()` reads the row's axis and
+  `stream_at_x0()`, cuts `view + offset` out of the ring, and hands the same offset to the
+  snapshot as its `x_offset`. `stream_at_x0()` follows the *display*: the moment `paused` is true
+  with no pause view published yet it answers `-display_epoch()`, which on a `Held` view is **0**
+  -- so the cut searched the ring at the event's edge-relative x, found nothing, and froze an
+  **empty** picture: `ev=0` on the probe's line, every measurement `--` and every ruler gone,
+  which is a much louder symptom than the empty margin above and reaches a user the same way
+  (pause while an event is on screen). Read first, it is the offset the axis is actually
+  displaying, which is what the whole scheme requires. The live case is unchanged -- there the
+  epoch does not depend on `paused()`, which is why the pause probe, which pauses a *live* view,
+  never saw it.
 - **The event axis is pinned from the snapshot's own stamps, not from the request.** A
   capture may legitimately be shorter than asked for — the ring need not reach back a
   full pre-trigger share on the first latch after arming, so `snap=[-0.339..1.000]`
@@ -158,6 +219,42 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   export.** Both need the same absolute index range over the time ring and every value
   ring, or an export and a capture of the same window would hold different samples. Call
   it under `mutex()`.
+- **Force is a synthetic edge, and the latch is still the only publisher.** The trigger panel's
+  Force button opens one capture at the *present* moment through `TriggerEngine::force()`: the
+  newest stored stamp becomes the event's own time and the engine enters the same pending state an
+  edge leaves it in, so the ordinary latch cuts, publishes, counts and frames the acquisition. A
+  forced acquisition therefore obeys every rule a latched one does — the axis pinned from the
+  snapshot's own stamps, a `pre_s` shorter than the request when the ring does not reach back that
+  far, and the frame that frames it being the one that consumes its `event_seq()` — and the button
+  owns no window, no publish and no framing of its own: **the event it publishes is cut by the same
+  code as a latched one.** Two things it deliberately does *not* do, both of them choices:
+  - **It skips the pre-window gate.** `force()` does not test `event_t - oldest_s_ >= pre_seconds_`:
+    "capture now" is a request for the history that *exists*, and refusing it because the ring is
+    young would refuse the one thing the button is for. The snapshot reports its own `pre_s`, and the
+    pin follows it — which is also how the pin gets *read*: with a request the ring cannot satisfy (a
+    100 s window at 99 % pre) the axis must come out a few seconds wide, where a pin stated from the
+    request would come out a hundred.
+  - **It does not restart a capture already filling.** That capture *is* the acquisition being asked
+    for: the display is already showing it fill (`live(capturing)`), and restarting it would throw
+    away the post window it has collected and move the marker to the press. The click is refused, and
+    named on stderr, rather than silently reinterpreted.
+  What the trigger *is* afterwards is still the mode's decision, and it is made where it always was —
+  in the latch: Normal leaves the engine armed with the latch's hold-off, Single disarms it. One
+  acquisition, whether an edge produced it or the button.
+- **The Force request is written under the model lock and consumed at the end of a packet.** It is
+  one atomic flag on `Acquisition` (`request_force()`), read with `exchange` after the channel loop
+  and before the `trigger_pending()`/`capture_edge()` publish — after the loop because the cut
+  `publish_event()` is about to make clamps to every value ring's `produced()`, so the newest sample
+  of every channel has to be in by then, and before the publish so the capture the click opened is
+  reported by the same packet that opened it. The *write* belongs under `ScopeModel::mutex()` and in
+  the same critical section as the `armed` flag the click also sets: the producer holds that lock for
+  a whole packet, reading the panel's `armed` at the top of one and the request at the bottom, so a
+  request written in between would be read by a packet whose engine was still disarmed and then
+  dropped — and dropped is right, because a momentary request must not be replayed later on a trigger
+  the user has stopped watching. With **no channel resolved** (no signal acquired) the click is
+  refused in the handler and not left to the producer: `on_data()` returns at once for a model with
+  no *streamed* channel, so a request parked behind that return would fire on the first signal
+  switched on afterwards.
 - **The trigger engine is not fed a reserved hole's samples.** A NaN comparison is false anyway,
   so the engine would not latch; but the real reason the samples are withheld is the other one:
   feeding them would advance the hold-off clock across time nothing was sampled in. The probe
@@ -180,18 +277,187 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   `process()` uses that for `last_trigger_s_`, `pending_start_s_` **and** the pre-window gate —
   all three, or the marker, the cut and the gate would disagree with each other by the width of
   a pulse.
+- **The trigger's whole input is the stored clock, so a clock that stops is a trigger that never
+  fires — and *that* is what a blank trigger-mode display is.** `Acquisition` feeds
+  `TriggerEngine::process(value, rel)` with the same `rel` it stamps the ring with, and the engine
+  has no other clock: the pre-window gate measures the event against the retained history
+  (`event_t - oldest_s_ >= pre_seconds_`), the post window counts *stream seconds* past the edge,
+  and `holdoff_until_s_` is set from `now_s` at the arm. A timeline that stands still therefore
+  reads as `history=0.0000/1.0000 s` for ever, on every line of `trig engine:`, no matter how many
+  samples arrive — and with no latch, `display_mode()` never leaves `Waiting`, whose bind is
+  *nothing* by design, so the plot is blank and the other traces are blank with it (the renderer's
+  bound window is empty too, so the same emptiness shows with the trigger off). Nothing about that
+  picture says "clock": it is "in trigger mode, with a math channel enabled, the data disappears",
+  which is how it reached a user. The reading is the `trig engine:` line's own pair — **`n` climbing
+  while `ring=[a..a]` stands still** — and the one-shot
+  `[udpscope] warning: the clock stalled ...` that `on_data()` prints at the first whole frame whose
+  stamps are all behind the clock. See
+  [invariants-data-path.md](invariants-data-path.md) for the two entries (a plan whose interval
+  moved under the stream; a frame accepted into a model with no streamed channel) and for why the
+  relative clock is accumulated in seconds.
+
+- **Persistence is the older acquisitions drawn *over* the current one, and "a layer is not a
+  signal" is what keeps them from becoming one.** Trigger mode may keep the last `N`
+  acquisitions -- `TriggerConfig::persist_depth`, the panel's *persistence* spin, 1 = the event
+  on screen alone -- and draw the older ones dimmer, which is the whole feature. The machinery is
+  the layer machinery the accumulate path already has: one **layer** per (signal, age), in the
+  same trace slot the accumulate path puts its own extra events in, named with the same suffix
+  vocabulary (` (A)`, ` (B)`, ` #4`), so `layer_base_name()` gives the base signal back and the
+  signal list, the colour resolver, the measurements and the layout writer all keep seeing **one**
+  signal where the plot draws several traces of it. Four consequences, each of which is a rule:
+  * **A layer slot holds no channel.** `RowSet::bind()` resolves a layer's *base* signal (it must
+    still be acquired -- switching a signal off takes its traces off every plot, layers included)
+    and then finds the channel **by name inside the snapshot** (`EventSnapshot::channel_names`),
+    because the channel list is renumbered by any structural change since that acquisition was
+    cut -- the rule `TriggerEngine` already follows, for the same reason. It leaves
+    `Row::channel[]` at `-1`, which is what makes every reader that asks "is this slot a trace of
+    a signal" skip it: the trace counts, the cursors pane's `mix` mask, the measurement marks, the
+    dump's per-slot lines, `collect_layout()`. A persistence layer is therefore invisible to the
+    signal list, the calibration table and the measurements by construction and not by a check;
+    the *measurements* go on describing the current frame because they resolve a channel from the
+    signal name the user configured, and `sine (A)` is not a signal anybody can configure.
+  * **Its brightness is a property of the slot, and it is applied where the trace is created.**
+    `Row::slot_alpha` is `RowSet::persist_alpha(age)` -- **half per acquisition**, so the schedule
+    is 1, 0.5, 0.25, 0.125, ... and the seventh layer is 0.8 %, i.e. gone; it does *not* depend on
+    the depth, so raising N adds dimmer acquisitions instead of restating the ones already on
+    screen. `install()` mixes `slot_alpha * trace_alpha_` into the trace's colour, because a
+    `Plot` fixes a trace's colour **at `add_trace()`** and a brightness nobody can set later is a
+    brightness that has to be a rebuild. Two things follow: a per-layer alpha is impossible
+    without a per-slot one, and **`set_trace_alpha()` is finally read** -- it was set by the
+    accumulate path and read by nothing, so an accumulation's "translucent, so agreement is
+    brightness" was opaque in fact while the docs claimed otherwise.
+  * **The dimmest trace is created first.** A `Plot` draws its traces in the order they were
+    created and cannot reorder them, so `install()` creates them sorted by brightness and the
+    *newest* acquisition is the ink on top. A layer drawn over the event would take its colour out
+    of the event's own trace wherever the two agree -- the opposite of what a persistence display
+    shows.
+  * **Every slot the plan does not fill is freed, and the plan does not depend on the data.**
+    `RowSet::sync_layers()` (called from the tick, before the frame's `bind()`) re-plans one layer
+    per (signal, age) into the row's free slots, *layer by layer* -- age 1 for every signal first,
+    then age 2, as the accumulate path does -- so a row that runs out of room draws the sharper
+    layer for each of its signals and stops. The plan is a function of the rows, the depth and
+    nothing else, so a **latch costs no rebuild**: the slot names and ages stay put and only the
+    snapshot behind them changes.
+- **An older acquisition is *drawn*, and it may not move anything.** The current event is the one
+  the axis is pinned to, and persistence must not disturb that, so `RowSet::event_data_window()`
+  -- the union the pin is re-stated from every frame while an event is held -- **skips layer
+  slots**: a wider older acquisition would otherwise re-pin the axis, and with it the window a
+  pinned measurement reads, which is a *measurement* moving because a display option was turned
+  up. The layers are bound only in `Held` and `Capturing` (a live view has no current event to be
+  the newest of them, a `Waiting` display is blank by design, and a pause view's stamps are on the
+  live window's clock, not on an edge): in `Waiting` and `Live` the layer slots are planned but
+  bound to nothing, and a trace with no series is not drawn and not listed in the legend. The one
+  thing they do share with the signal is the **row's y axis**, so the y auto-fit sees them -- a
+  y axis that ignored the traces it draws would clip the excursion the display exists to show.
+- **A retained acquisition is a whole window copy, so the depth is capped by bytes and by what a
+  row can draw.** `publish_event()` moves the outgoing `event()` into the retention before it
+  publishes the new one: `ScopeModel::persist_event(age)` is the event `age` latches back, one
+  atomic `shared_ptr` slot per age, read by the tick without a lock exactly as `event()` is.
+  `snapshot_bytes()` is the honest cost of one -- both stamp arrays, every channel's `f32` samples
+  and the LOD pyramids built for them, i.e. ~4.5 bytes per sample per channel plus 8 per sample of
+  clock -- and `prune_persist_locked()` cuts the set to **both** bounds: the depth, and
+  `persist_budget_bytes()`, which is the planned ring bytes (`Partition::bytes()`), because persistence is a copy
+  *of* what the rings hold and holding as much again is the honest ceiling for a display of it.
+  `kMaxPersistDepth` is 8 for the different reason the panel needs one: the layer there is already
+  invisible (0.8 %) and seven is all the free slots a one-signal row has. The depth is not the only
+  thing that limits what is *drawn* -- a row of `S` signals with 8 slots shows
+  `floor((8 - S) / S)` ages of each, so the default four-signal row shows one older acquisition
+  and a row per signal shows all seven. The two shortfalls are **separate readings**, and a caller
+  that conflated them would report a shrunken display as complete: a *slot* shortfall is
+  `placed < want` (what `RowSet::sync_layers()` returns against what the depth asked for), while a
+  *budget* shortfall is a `kept` below the depth plus the count `persist_dropped()` carries -- and in
+  that case the layer slots **exist and draw nothing at all**, so `layers=`/`placed=` alone say
+  nothing is wrong. The panel's notice therefore names both numbers -- `D of W layers fit, K of A
+  older acquisitions retained` -- because a user who asked for eight layers and sees two has no other
+  way to tell "the display is deliberately shallower" from "the feature is broken".
+- **Depth 1 is not a mode, it is the *absence* of one.** `persist_depth = 1` retains nothing at
+  all -- no copy, no layer, no rebuild -- and `set_persist_depth()` prunes the set **at once**
+  rather than at the next latch, because lowering the depth is a user asking to stop paying, and a
+  trigger that has stopped firing never reaches another publish. A depth change is therefore also
+  how the memory comes back.
+
+- **The phosphor density is the *trace*, and that is a different display from the layers above, not a
+  mode of them.** The trigger panel's `Advanced` block offers both, and the words matter: *multiple
+  events* is `persist_depth` (N retained acquisitions, N traces, dimmer with age) while *persistence*
+  is `TriggerConfig::density` -- the plotter's `Plot::set_density()`, an intensity grid
+  **per trace, drawn in that trace's own colour**, every acquisition deposited into it, which fades
+  either by a time constant or by a per-acquisition factor. There is **no depth** on the density and
+  no per-acquisition memory: the image is `traces * columns * rows * 4` bytes, and both factors are
+  bounded -- the grid is the row's axes rect in device pixels **up to the plotter's
+  `kDensityCellCap`**, and there is one grid a trace the row draws. Four traces in a row
+  therefore hold at most 4 MiB between them, whoever dragged the window where (the probe's
+  one-signal-per-row run reads `cells=1044714`, 4 178 856 bytes), so a thousand acquisitions cost
+  what one costs and *neither* a wide window nor a long run can make the image grow. A cell's value
+  is a number of *sweeps*: the library
+  deposits a cell once per trace per sweep however many of that trace's own samples crossed it
+  (`[density-probe] on` reads `peak=1.0000` for one sweep; a per-hit deposit read 18) -- dwell is
+  `Style::intensity_grading`'s question, not this one's. The colour is the trace's own
+  (`RowSet::signal_color()`, the same source the trace was built with and never a second one), so a
+  saturated cell is that signal's colour at full strength and two signals agreeing in a cell are two
+  quads of two colours rather than a blend.
+  Five things hold it together, each of which is a rule:
+  * **It is a trigger-mode display.** `apply_density()` (the tick) states `Held` and `Capturing` as
+    the states it is on in; `Live`, `Waiting`, `Paused` and a file are not, and turning it off drops
+    the grids **at once** rather than at an acquisition a quiet trigger never sends (the rule
+    `set_persist_depth()` follows). So it goes away with the trigger, and a re-enable starts from an
+    empty image rather than a stale one at another scale.
+  * **One deposit per acquisition, one frame *after* the frame that frames it.** `Plot::accumulate_density()`
+    deposits what the plot currently holds through the transforms of its **last** layout, because the
+    frame's own layout is computed inside the paint that follows the tick: `density_pending` is set
+    where a snapshot is *framed* -- beside `record_pending` -- and consumed by the next tick, so the
+    deposit is of the new acquisition drawn at the axis that acquisition is pinned to. Doing it in the
+    same tick was right on the common Held-to-Held transition and wrong on the first latch, whose axis
+    was still the live ring's.
+  * **The switch deposits what is already on screen.** `on && !density_was_on` sets the same pending
+    flag, so a user who turns persistence on while an event is held sees it instead of waiting for a
+    latch that `single` mode may never send.
+  * **No trace is drawn over it, and the newest acquisition is inside it.** `Renderer::draw_traces()`
+    returns at once while a density is on: the trace ink *is* the image, so the acquisition just
+    deposited is a sweep in it and fades with the rest. Drawing the polyline too put a solid,
+    unfading stroke over its own faint ghost -- the reported "persistent image + last acquisition",
+    where the last acquisition never faded in time mode -- and the assertion is a **framebuffer** one:
+    `a_phosphor_density_is_the_trace_in_its_own_colour` reads the same pixel before and after one
+    time constant and requires it dimmer (`full=224 -> faded=115`, the trace's own `0xE0` green),
+    which a stroke over the density could not do.
+  * **The brightness ceiling is the trace's own brightness, and the ramp is linear in sweeps.** The
+    app leaves `DensityConfig::full_scale` at the library's default of **one sweep** and `gamma` at
+    1.0, so the acquisition just deposited reads as the trace it is a picture of and a signal crossing
+    the same place every acquisition settles *at* the trace's colour (the ceiling clamps), rather than
+    a fraction of a brighter steady state. The old ceiling -- the fade's steady state, `1/(1-factor)`
+    for the acquisition fade -- is the gain offset a user reported between the latest acquisition and
+    the persistent image, and the "dimmer by design" headroom that made the ramp visible is reversed
+    here.
+  * **It is the plot's, so a figure rebuild resets it** -- the grids live on each `Plot`, and
+    `rebuild_all()` builds new ones. That is the one state a structural change (a row added, a signal
+    switched off, a trace recoloured) does not carry: it costs the accumulated image and nothing else,
+    and the alternative -- keeping the grids in the `RowSet` -- is what would make it not a plot
+    feature. The layout is unaffected either way: the density reserves no space and nothing on it can
+    be picked, exactly as `set_invalid_spans()` does.
+  * **The session carries it.** `trigger_density`, `trigger_density_decay`, `trigger_density_tau` and
+    `trigger_density_factor` in the layout file, written whether or not it is on -- a display set up
+    once and switched off is still the display you come back to. The decay is the *word* the panel's
+    dropdown shows ("acquisitions"/"time"), for the reason the condition's shapes are text.
 
 ## A latch is also a file
 
-The pane that lists the cache is **on demand**: the toolbar's event-history button and the pane are
-collapsed until it is asked for, because a column of stale events beside a live plot is what a user
-who has stopped looking at events does not want. What makes it *available* -- (recording is on) or
-(an event is on screen) -- is decided in one place, `sync_events_availability()`, so the button and
-the pane cannot disagree; a disabled cache with nothing being examined takes the button away *and*
-collapses the pane, because a visible empty column is what "off" must not look like. Trigger mode is
-deliberately **not** one of the conditions: a stored event being examined is a file, which has no
-trigger, and tying the pane to the trigger would close the list under the click that opened an event.
-The recording switch lives in the trigger panel, not in the pane it empties.
+The cache is listed twice, from one `EventStore::list()`: the dock's compact **Events block** and the full list on the
+`events` slide-over page (the left pane, its divider and the header toggle are gone, so events no longer take
+any of the plot's width). What makes it *available* -- recording is on, **or** a replay is on screen, **or** the
+cache already holds something (`event_recording || replaying || events_cached`) -- is decided in one place,
+`sync_events_availability()`, and it sets the block's sensitivity (`dock_events_set_sensitive()`) and the page's
+(`events_box`) from the one `available`, so they cannot disagree. Unavailable means **insensitive, never hidden**
+("disable, do not hide"): the block stays on screen greyed, and turning recording off with the page open leaves it up
+and greyed rather than stale and live.
+
+**This deliberately differs from the redesign spec**, which has the block insensitive "outside trigger mode". Trigger
+mode is *not* one of the conditions: a stored event being examined is a file, which has no trigger, and a replay or a
+group *leaves* trigger mode, so a block that went grey outside trigger mode would grey itself under the very click
+that started the replay -- the one-click replay in the dock would disable the dock it was clicked in. Do not "fix" this
+to match the spec. The recording switch lives in the trigger panel, not in the block it empties.
+
+The two views follow the latch on different cadences: the dock is rebuilt on **every** latch (`record_event()`), the
+page's list only while the page is open, and `open_events_page()` refreshes it when it was closed; a caller that
+opens the page any other way shows a list that is as stale as the last time it was open.
 
 ## Opening a file is a detour, so *Go live* is a restore
 
@@ -224,13 +490,18 @@ is the complaint this answers.
   - `rebuild_trigger_signals()`, finding a `channel` of `-1` after the rebuild renumbered the
     channels, silently settles on the first signal *and* re-defaults the level -- which is why
     `trigger_level_touched` is restored with the configuration.
-- **It waits for the stream's own channel list, gated on `generation()` having moved.** The restored
-  name has to be resolved against the live channels, and those do not exist until the first CONFIG of
-  the restarted client lands on the producer thread. `App::live_restore_generation` is the generation
-  read when *Go live* was pressed; `live_restore_pending` stays set until it differs **and**
-  `channels()` is non-empty. A `pending=1` that never clears is therefore a reading about the
-  *stream*, not about the restore -- see `invariants-session-and-export.md` for the save that made it
-  stick at `channels=0`.
+- **It waits for the trigger's channel *name* to resolve again, not for `generation()` to move.** The
+  restored name has to be resolved against the live channels, and a file view that renamed its channels
+  (`square (A)`) must be gone first or the name selects the wrong signal. `App::live_restore_pending`
+  stays set until `channels()` is non-empty **and** a channel carries the snapshot's name (or the
+  snapshot named none). Gating that on the generation was wrong in the common case: a *single* event
+  keeps the stream's own channel names, and the restarted client's CONFIG is identical, which the model
+  treats as **no change on purpose** (`same_stream_signals()`) -- so the generation never moved and the
+  restore waited for something that could not happen. What shook it loose was toggling the trigger,
+  which *is* a structural change: "click live, then toggle the trigger a couple of times" was the
+  symptom. A `pending=1` that never clears is a reading about the *stream* (no channels yet), not about
+  the restore -- see `invariants-session-and-export.md` for the save that made it stick at
+  `channels=0`.
 - **Only the two controls a file view actually moved are restated** -- the signal dropdown and the
   level spin. The rest of the trigger panel was never touched, and writing to a control fires its
   handler, so the ones with nothing to put back are left alone. Both writes are inside

docs/claude/verification.md

@@ -13,30 +13,57 @@ xvfb-run -a env UDPSCOPE_EXIT_AFTER_MS=8000 UDPSCOPE_ENABLE_ALL_MS=1000 \
   ./build/udpscope --server 127.0.0.1 --port 8000
 ```
 
-Two baselines every run is read against. A clean build emits **four** warnings and no more: two
-`-Wmissing-field-initializers` on `MathNode::source` and `-Woverlength-strings` on **both**
-generated GResource `.c` files — the help pages' and the icons', whose blob crossed C99's
-4095-byte string-literal limit when the two app icons joined the four action ones (a note about a
-generated file, which GCC itself supports). The fifth warning that used to appear here was an unused
-`output_built` in `math_probe()`; it was **deleted** as dead code — redundant with the
-`output_after_add` already printed on the same line — and that deletion is what dropped the baseline
-from five to four. Nothing started reading it. And an exit-dump run emits **no** `Gtk-CRITICAL` at
-all. A fifth warning, or any critical, is a finding.
+Two baselines every run is read against. The UDPS runs must be **unchanged by the source-plugin work**:
+a UDPS self-check, number-normalised (`sed 's/[0-9.]\+/N/g'`), diffs empty against one taken before it.
+For the badge bar / slide-over / dock redesign the same diff is taken **against the commit before that
+series (`c572ec2`)**, from a fresh `XDG_CONFIG_HOME` on each side (a stored mock session changes the
+trigger lines), and it is "unchanged except" exactly these lines: `panels:` loses `switcher=` (the
+trigger form is read through the slide-over, so its width and height change, and the `compact arm
+probe` width with them); `switcher:` becomes `dock: shown= sensitive= w= scroller_pages=`;
+`panel controls:` prints `dock=` for `switcher=`; `help figures:` loses `side_switcher=`, replaces
+`side_stack=` with `badge_bar=` and `dock=`, moves the `trigger_*` rectangles into the slide-over and
+shortens `plot=` by the 36 px bar; and the `tour started: steps=` count. A self-check taken **before**
+`c572ec2` is no longer the baseline for those lines. The rest is the mock's own jitter (the sign of a
+`square y=[...]` or a `trig engine:` figure, the position of one `trigger: edge` line), which the
+normalisation does not remove -- anything else is a finding.
+For the horizontal plot split the same diff is taken against the commit before it (`18b91c8`, with
+`deps/plotter` at its pre-split pin `f79a97b`), and it is "unchanged except" exactly two things on the
+layout lines: **`buttons=`** grows (the editor now carries the cell `+` buttons and the column arrows:
+`3P + 2F + 2` for `P` plots in `F` figure rows, so `5 -> 7` for one row and `8 -> 12` for two), and the
+layout probe line and the exit dump's layout line gain the **`cells=[..] colweights=[..]`** fields.
+Everything else -- cursors, measurements, readouts, signal pages, math, trigger, help figures, the
+E-1608 -- reads as before; a difference there is a finding, not the feature. Take a second baseline run
+as a jitter control before believing one (a few mock readings, such as the sine's membership of the
+cursors mix list or a V/mV flip, move between two runs of the *same* build).
+A clean build emits **one** warning and no more: a `-Woverlength-strings` on the icons'
+generated GResource `.c`, whose blob is **10146** against C99's 4095-byte string-literal limit with
+the six action icons and the two app icons that remain (a note about a generated file, which GCC
+itself supports). History: the help pages' generated `.c` (**516044** bytes) went when the manual
+became a Mallard set installed for Yelp; an unused `output_built` in `math_probe()` was deleted as
+dead code; and the last two, `-Wmissing-field-initializers` on `MathNode::source` in `math_probe()`,
+went when the probe's `MathNode{MathOp::Gain, {}}` / `MathNode{MathOp::LowPass, {}}` named the
+field (a partial brace-initialiser on `MathNode` re-adds one: `source` has no default member
+initialiser). Re-measure by touching `src/icons/udpscope.gresource.xml` and rebuilding; any
+second warning is a finding. And an exit-dump run emits **no** `Gtk-CRITICAL` at all, nor any `Gtk-WARNING`: the dump's
+`gtk warnings:` line counts GTK's own log (through a writer function — GTK is built with structured
+logging, so the handler API never sees its messages) and must read `0`; see
+[probe-readings.md](probe-readings.md).
 
-An *incremental* build reads **two** of those four: the generated GResource `.c` files are not
-recompiled when only `src/` changed, so their `-Woverlength-strings` do not reappear.
+An *incremental* build reads **zero**: the generated GResource `.c` is not recompiled
+when only `src/` changed, so its `-Woverlength-strings` does not reappear.
 
 A third reading every run offers for free: **how many `[udpscope] buffer allocated:` lines it
 printed.** The line is not behind a probe — it is in every build — and one line is one *real* change
 of buffer plan, each of which blocks the main thread for the time it takes to touch the whole
-`--buffer-mb`. A normal run prints two or three. Fifteen at startup is the defect it was added for;
+planned buffer. A normal run prints two or three. Fifteen at startup is the defect it was added for;
 see [probe-readings.md](probe-readings.md).
 
 That second baseline used to be "exactly two, `gtk_widget_get_height` and `gtk_widget_get_width`,
 from the dump asking a destroyed widget for its size", and tolerating them was a mistake: the dump
 runs from the destroy handler, so the widget pointer is **freed memory**, and a critical is only
 the lucky reading of it. A run that had built and destroyed other windows first —
-`UDPSCOPE_PROBE_HELP_MS`, which opens three — has had that memory reused, and the same two calls
+`UDPSCOPE_PROBE_HELP_MS`, which opens the About and shortcut dialogs and then closes them — has had
+that memory reused, and the same two calls
 then **SIGSEGV in the middle of the dump**, which reads as a truncated dump rather than as a
 crash in a debug line. Every size the dump prints is therefore captured on the *tick*, while the
 window is alive (`App::dbg_*`), and **no `gtk_widget_*` call may appear in the dump** — the
@@ -50,6 +77,115 @@ precedent, not an exception.
   `UDPSCOPE_TRIG_TRACE_MS` — schedule individual probes. `UDPSCOPE_PROBE_DISARM_MS` only
   *starts* its sequence: it switches the trigger on and then polls for a capture to open,
   so the Disarm lands ~300 ms into one rather than wherever a fixed delay happened to fall.
+- `UDPSCOPE_PROBE_FORCE_MS` — the trigger panel's **Force** button: one acquisition at the present
+  moment, with the pre/post window the panel is set to, without waiting for the condition. It is a
+  chain, not an instant — `MS` is when it *starts*: it forces trigger mode **off** through the toggle
+  (a session file remembers the trigger, so the off state is stated rather than assumed) and reads the
+  button's stated state 300 ms later; it then sets a level no mock signal reaches (9 V), a 2 s window
+  at 50 % pre, acquires the mock's `sine` and turns the trigger on; it presses Force 2.5 s after that
+  (the window write re-plans the buffer and clears the history, so the ring needs the time to fill
+  past the 1 s leg A asks for); it presses a second time on a 100 s window at 99 % pre — a request no
+  run this short can satisfy — 400 ms after the first latch. **Run it alone, against the plain mock**,
+  with time for both legs:
+
+  ```sh
+  python3 tools/mock_udpstreamer.py --port 8114 --rate 10000 --batch 100 --duration 30 &
+  sleep 1.5
+  xvfb-run -a env UDPSCOPE_EXIT_AFTER_MS=14000 UDPSCOPE_PROBE_FORCE_MS=3000 \
+    ./build/udpscope --server 127.0.0.1 --port 8114 2>&1 | \
+    grep -E 'force-probe|trigger:'
+  ```
+
+  Being alone is load-bearing twice: the level is chosen so the engine *cannot* latch on its own, so
+  a latch count that moves is the force's and nothing else's — any other probe that arms a reachable
+  condition adds latches of its own — and `UDPSCOPE_ENABLE_ALL_MS` before it would acquire four
+  signals, which changes the level's default range and the plan. Two lines per pass are in
+  [probe-readings.md](probe-readings.md); **`latches=P->Q` with `Q == P + 1`, `display=event(frozen)`,
+  `matches_request=1` in leg A, `pin_is_snapshot=1` in both** are the assertions, and leg B's
+  `matches_request=0` is *expected* — a ring that cannot reach back 99 s is the only state where
+  "pinned to the snapshot, not to the request" is a reading rather than a coincidence.
+- `UDPSCOPE_PROBE_PERSIST_MS` (+ `UDPSCOPE_PROBE_PERSIST_DEPTH`, default 4, 1..8) — the **persistence
+  display**: trigger mode keeps the last N acquisitions on screen, each older one drawn at half the
+  previous one's brightness. It enables the signals itself (one call, as a restored session does) and
+  arranges one signal per row — the arrangement the app gives an opened file, and the one with room
+  for every age — sets the depth **through the panel's own spin**, arms the trigger on the mock's
+  `square` and polls until the retention is full: an event on screen and as many older ones kept as
+  the depth asks for. The depth is *left* where it put it, so the run's own tail is the display at
+  that depth:
+
+  ```sh
+  python3 tools/mock_udpstreamer.py --port 9541 --rate 500000 --batch 1000 &
+  PY=$!; sleep 0.5
+  xvfb-run -a env UDPSCOPE_EXIT_AFTER_MS=16000 \
+    UDPSCOPE_PROBE_PERSIST_MS=2500 UDPSCOPE_PROBE_PERSIST_DEPTH=4 \
+    ./build/udpscope --server 127.0.0.1 --port 9541 2>&1 | grep -E 'persist-probe|persistence:|layout:'
+  kill $PY
+  ```
+
+  **Not with `UDPSCOPE_ENABLE_ALL_MS`**: that probe ends by switching a signal off two seconds later,
+  which takes the row that plotted it — and its layers with it — out of the middle of the measurement.
+
+  **Read it as a pair of runs**: the same command at `..._PERSIST_DEPTH=1` is the display *without*
+  the feature, so its `kept=0`, `layers=0`, `bytes=0` and its `layout:` line holding only the signals
+  is the "N = 1 is exactly the old behaviour" reading, and it is also the run the exit dump's
+  `frame cost:` line is compared against — the tick/draw means are means over the whole run, and the
+  depth is raised at `MS`, so the difference is a *lower bound* on what the layers cost. **`ev_is_snap`
+  and `pin_is_snap` must be 1 in both runs**: the older acquisitions are drawn and never pinned, so
+  the axis, the framing and the measurements still describe the current event. `alphas=` is the decay
+  schedule in use, oldest first — halves, and `1/2^age` at that. Both lines and the two exit-dump
+  lines are in [probe-readings.md](probe-readings.md).
+- `UDPSCOPE_PROBE_DENSITY_MS` (+ `UDPSCOPE_PROBE_DENSITY_TAU`, default 1.0 s) — the **phosphor
+  density**: an intensity image **per trace**, in that trace's own colour, the axes rect in device
+  pixels up to the plotter's `kDensityCellCap` (past which it scales the rect down uniformly and
+  magnifies the image back over it with a linear filter), every
+  triggered acquisition accumulated into it (the newest included), drawn *in place of* the traces,
+  fading by a per-acquisition factor or by a time constant. It states the display
+  **off** through the panel's own switch first, so the `off` leg is the run without it, then arms the
+  trigger on the mock's `square` with one signal per row — the arrangement the persistence probe uses
+  — and only then switches it on, so the acquisition already on screen is the first image. Four legs,
+  each a separate `g_timeout`, so whole frames happen between them:
+
+  ```sh
+  python3 tools/mock_udpstreamer.py --port 9551 --rate 500000 --batch 1000 &
+  PY=$!; sleep 0.5
+  xvfb-run -a env UDPSCOPE_EXIT_AFTER_MS=14000 \
+    UDPSCOPE_PROBE_DENSITY_MS=2500 ./build/udpscope --server 127.0.0.1 --port 9551 2>&1 | \
+    grep -E 'density-probe|density:'
+  kill $PY
+  ```
+
+  **The assertions, in order:** `off` reads `rows=0 traces=0 cells=0 ink=0.0 peak=0.0000` (there is no
+  grid at all); `on` reads `rows=4` — every row has its own image, one per trace in its own colour,
+  so `traces=4` with one signal a row — and **`peak=1.0000`**, one sweep's ink
+  being one per cell it covers; `step-acquisitions` reads **`peak=1.5000`**, which is the panel's
+  0.5 applied to the old image plus the new sweep's own pass; and `step-time` reads
+  **`ratio=0.367879`**, one step of `dt = tau` through the plot's own `decay_density()`. A `peak` in
+  the tens for the `on` leg is the *per-hit* deposit -- one sweep counted once per sample that
+  crossed a cell -- which saturates a single acquisition and hides the sweeps behind it. The line
+  also carries the app's own A/B of the frame cost (`tick`/`draw` before and after the switch, in
+  one run), and the exit dump's `density:` line says what the last frame it was on held. Both lines
+  and the dump line are in [probe-readings.md](probe-readings.md).
+
+- `UDPSCOPE_PROBE_NOTRACE` (no value; **not** a scheduled probe, and off unless it is set) — the
+  per-paint detail behind the exit dump's `traceless paints:` counter: one `[notrace]` line for each
+  of the first 40 paints after the first bind that staged no trace, naming the mode, the axis the
+  frame was asked for and every slot's bounds. It is behind a variable because a state that draws
+  nothing lasts as long as it lasts, so an ungated line is one per frame for the whole time -- and it
+  is *not* printed for a frame a phosphor density is drawing, which stages no trace by construction
+  (the frame's ink is the image) and would otherwise be counted as well. The counter itself is in
+  every build; see [probe-readings.md](probe-readings.md).
+
+- `UDPSCOPE_PROBE_HEADER` (no value; **not** a scheduled probe) — the once-a-second
+  `[udpscope] header: window_button_w=… bar_w=…` line. The widths are sampled either way (the
+  exit dump reads them); the line is behind this variable because it is detail behind that
+  reading, not a line every run should print. An unallocated window reads `0` for both.
+- `UDPSCOPE_PROBE_RENDERER` (no value; **not** a scheduled probe) — the renderer pair
+  `--renderer` should have exported, printed from `main()` before GTK initialises
+  (`[renderer] option=… GSK_RENDERER=… LIBGL_ALWAYS_SOFTWARE=…`), then the renderer GTK
+  built (`[renderer] realized=…`) once the window has one. Run it with `--renderer cairo` to
+  check the option reaches the environment before `gtk_init()`/`adw_init()`; run it without
+  the option to check the default is untouched.
+
 - `UDPSCOPE_PROBE_TRIGRENUM_MS` — the trigger's capture must survive a **renumbering of its own
   channel**. It sets the reported geometry through the real widgets (1 s window, 10 % pre share,
   hold-off from `--holdoff`) on the mock's *square* alone, polls for a capture to open, and then
@@ -69,6 +205,35 @@ precedent, not an exception.
   with, so a synchronous sequence would read every position one action stale. It clicks by
   emitting `::clicked`, never `gtk_widget_activate()`, which holds a `GtkButton` for its
   250 ms `ACTIVATE_TIMEOUT` and then emits into a button the rebuild has already destroyed.
+- `UDPSCOPE_PROBE_SPLIT_MS` — drive the horizontal plot split, 28 steps 250 ms apart (so a run needs
+  `UDPSCOPE_PROBE_SPLIT_MS=1500 UDPSCOPE_EXIT_AFTER_MS=12000` at least; it enables and assigns the
+  signals itself, so `UDPSCOPE_ENABLE_ALL_MS` is not needed). Each step restructures the cells,
+  re-points the area at the new figure and lets the *next* step read a frame that was actually laid out
+  with them, which is why every report line describes the previous step's change. It splits and
+  weights a row, fills the caps, round-trips a session through `collect_layout()` / `save_layout()` /
+  `load_layout()` / `apply_layout()` (and a copy with its `row`/`width` lines stripped), clicks the layout
+  editor's real cell `+` button, drives the column drag handler, and checks the signals page, the drop's
+  `row_at()`, the cursors pane's ruler labels and the shared y axis of a split row (`shared-y`). Run it once, serially, on its own mock port, from a
+  fresh `XDG_CONFIG_HOME` (the probe deletes the temp files `udpscope-split-probe.toml` and `.legacy` it
+  writes under `g_get_tmp_dir()`, but the editor's clicks schedule a real session save). Read it against
+  the `[split-probe]` section of [probe-readings.md](probe-readings.md); the run must still end with
+  `gtk warnings: 0`.
+- `[levels-probe] N measurement(s) over K channel(s), shares='...' -> W window(s), L level
+  walk(s)` (stderr, `UDPSCOPE_PROBE_LEVELS_MS`) — **prices a measurement pane**, which is what a
+  report of "it is slow with many measurements" has to become before it is a number. It adds one
+  `above` per share in `UDPSCOPE_PROBE_LEVELS` (comma separated, default `50`), spread in turn
+  over the first `UDPSCOPE_PROBE_LEVELS_CHANNELS` channels (default 1), and reports the two
+  things a count does not name: how many **windows** (one `MeasureWindowReader`, one fetch, one
+  scan per measured channel) and how many **level walks** (one accumulator per *distinct* share)
+  the pass then had to take. `50,50,50,50` on one channel is four pane rows and **one** walk;
+  `5,10,15,20` is four rows and **four**; the same four shares over four channels is four
+  windows *and* four walks. Read the `measure cost:` line it leaves in the exit dump and the
+  sweep in [invariants-measurements.md](invariants-measurements.md) — and read it against a run
+  with `UDPSCOPE_PROBE_LEVELS_MS` unset, because the pane's cost is a *difference* between two
+  tick means. **Run it at the scale being asked about**: the cost is the window's, so a 2 s
+  window prices a 15 s one at nothing (four measurements over four channels read `35.69 ms` a
+  recompute and a 4.58 ms tick mean at a 15 s window against `6.58 ms`/1.34 ms for one window at
+  the same window).
 - `[measure-probe] N measurements on 'X'` (stderr, `UDPSCOPE_PROBE_MEASURE_MS`) — adds one
   measurement of each statistical type (average, top, peak to peak, amplitude) on the first
   *channel* and forces a recompute. It must name a **channel**, not `signals().front()`: the
@@ -77,13 +242,37 @@ precedent, not an exception.
   collecting anything -- that is how the first baseline of the stall below read 0.4 ms).
   The values are in the exit dump as `measurements: <type>=<value>`; on the fast mock
   (`tools/mock_udpstreamer.py --rate 1300000 --batch 2000`) a unit sine must read
-  `peak to peak=2`, `amplitude=1`, `average=0` and **`top=0.636620`** -- 2/pi, the half-wave
-  mean of a sine, which is the check that the threshold types are not merely plausible.
-  `[measure-trace] view=[..] <type>=<value>... marks=N level:V/time:V...` is a repeating line
-  (250 ms) from the probe: the pane's numbers beside the *current* window and the marks actually
-  placed, which is the only way a stale result or a mark that should not be drawn shows up as a
-  number. It must never print `marks=0` while measurements with `show_on_plot` are on and the
-  data is there -- that was the rulers blinking off at a mode change.
+  `peak to peak=2` **exactly**, `average=0`, and the two flat-level types as their definition
+  says: **`top=0.957988`** and `amplitude=1.915983`. `top` is no longer 2/pi -- it is the *flat*
+  level of the upper side, read from the density of the window's buckets, and a sine has no
+  plateau so the densest band is at its peak; `amplitude` is `top - bottom` (a scope's
+  `Vamplitude`), not the half-swing it once was. The check that the flat levels are *levels* and
+  not extremes is the same probe against the mock's `square` (`--square-harmonics 30`, the
+  control being `0`): `top`/`bottom` `0.999983`/`-0.999983` rippled against `1.000000`/`-1.000000`
+  ideal, `amplitude` `1.999966` against `2.000000`, while `peak to peak` reads `2.358701` rippled
+  against `2.000000` ideal -- the ±1.179 edges'
+  overshoot, kept by the extremes and excluded by the levels. The per-type values, the reason for
+  each, and the cost of the histogram are in
+  [invariants-measurements.md](invariants-measurements.md).
+  `[measure-trace] mode=M view=[..] s0=S swin=[..] pin=[..|off] for=[..] passes=N
+  <type>=<value>... marks=N level:V/time:V...` is a repeating line (250 ms) from the probe: the
+  pane's numbers beside the *current* window and the marks actually placed, which is the only way a
+  stale result or a mark that should not be drawn shows up as a number. `swin` is `view` moved onto
+  the stream's clock by `s0` (`stream_at_x0()`), `pin` is the pin's own extent in that clock (`off`
+  when nothing is pinned) and `for` is the window the printed numbers were computed over -- so a
+  reading that moved while `view` stood still is a change of `s0` (a new snapshot under the same
+  mode) and not a stale pass, and only these fields tell those apart. `passes` beside them says
+  whether a recompute answered the move. **While the view is pinned, `for` must equal `pin` -- and
+  `swin` is free to sit anywhere inside it** -- through any number of zooms and pans: a latched
+  event's numbers are the *frame's*, so a gesture inside the pin changes neither them nor `passes`.
+  Read the other way round it is the defect: `for` following `swin` into the zoom while the values
+  move is the reported "on a still frame the measurements change when I zoom". Neither reading is
+  the old "measurements stand still while the data moves", which was `for=[0.47..2.47]` against a
+  `swin=[1.417..1.467]` with `passes` frozen -- the pane describing a window the plot had left.
+  The line must also never print `marks=0` while measurements with `show_on_plot` are on and the
+  data is there -- that was the rulers blinking off at a mode change. `pin=off` while the mode is
+  `held` is not a stale reading but the window control: `apply_time_window()` unpins, and for those
+  frames the view is live-framed and measuring the viewport is right.
   `measure cost: N recomputes, X ms total, Y ms each, data D ms (P%), covered=C buckets=B
   raw=R (F%), N ns/covered sample` follows it: **read it against a run with
   `UDPSCOPE_PROBE_MEASURE_MS` unset**, because a frame mean cannot attribute a cost. The last
@@ -99,13 +288,64 @@ precedent, not an exception.
   (`tools/mock_udpstreamer.py --rate 1300000 --batch 2000`), where a window is ~2 M samples.
   `--noise 0.1` there reads **2.0%** at 1.96 ms a recompute against the clean 0.1% at 1.41 ms, and
   that is the interferer's own cost rather than a regression -- the figure to compare a change
-  against is the **clean** one.
+  against is the **clean** one. `raw` is also the guard on the flat-level types, which are the one
+  thing that reads a second time: `top`/`bottom`/`amplitude` fold a histogram out of the **same**
+  fetched bucket list, so they add buckets and not samples (measured: `raw=0.1%` and `2.1%` with
+  the interferer, against `0.1%`/`2.1%` before those types had a flat level, for 0.44→0.50 ms and
+  0.52→0.65 ms a pass -- the buckets are the budget). It is the guard on the band averages for the
+  same reason: `between` is a *second level in the same walk*, not a second pass, and measured on
+  the fast mock at a 2 s window with the measurements probe adding one of **every** type, `raw`
+  stayed at a fraction of a percent of `covered` —
+  `covered=240719031 buckets=3760828 raw=113966 (0.0%)` for the ten types before, against
+  `covered=255372033 buckets=3989978 raw=134978 (0.1%)` for the thirteen after, at 0.8 → 1.1
+  ns/covered sample (`data` 156.85 → 178.38 ms: the pane holds three more measurements and one more
+  level, and both walk the same fetched bucket list).
   Note the **final** `measurements:` line and `[measure-trace]`'s last lines may read `--`:
   `UDPSCOPE_EXIT_AFTER_MS` arms the trigger before it dumps, so the dump can land in `Waiting`
   with nothing bound and the axis at its default. The race-free reading is an earlier
   `[measure-trace]` line, which carries its own `view=`; those lines are also where the
   level-mark fallback is visible (an invalid pass must still print its `level:` marks).
 
+- `[bandavg-probe]` (stderr, `UDPSCOPE_PROBE_BANDAVG_MS`) — the **band averages**:
+  `above`/`below`/`between`, the plain means over one side of a share and over a band, which are
+  *different numbers* from `top`/`bottom`'s flat levels (see the band-average invariant in
+  [invariants-measurements.md](invariants-measurements.md)). It adds seven measurements, on the three
+  shapes whose band means can be computed by hand, and the four figures to read are:
+
+  * the 1 Hz unit sine at a **2 s window**: `above 50` = **`0.636620`** (2/pi) and `below 50` =
+    **`-0.636620`** — the exact figures the old `top`/`bottom` documented, and the reason this type
+    exists at all; `between 50 75` = `0.255873` (`3(2-sqrt 3)/pi`), an interior mean no side and no
+    whole-window statistic reports;
+  * the mock's band-limited `square` (30 harmonics, its default): `above 50` = **`0.986496`**, the
+    reading the commit that made `top` a flat level recorded as the *old* `top`;
+  * the mock's `ramp`, whose density is uniform: `between 50 75` = `0.250000` and `above 50` =
+    `0.500000` — a band's mean *is* that band's centre, so the shape predicts the number;
+  * and the two nothing-to-measure readings: `above 100` on the `ramp` and `between 50 75` on
+    `--square-harmonics 0` (whose samples are all exactly +/-1) must be `invalid`/`--`, never 0.
+
+  **Run it at a 2 s window** (the probe waits for a full one before it reads anything — the mock
+  delivers about 0.5 MS/s of the 1.3 MS/s it declares, so a freshly enabled ring needs seconds of
+  wall clock), and **not** with `UDPSCOPE_PROBE_MEASURE_MS` or `UDPSCOPE_PROBE_MEASURES_MS`: all
+  three add measurements to one pane. `UDPSCOPE_EXIT_AFTER_MS=17000` covers its sequence. The
+  command, both mock flavours and the lines are in [probe-readings.md](probe-readings.md):
+  `--square-harmonics 30` for the `0.986496` and the `0.302744`, `--square-harmonics 0` for the
+  `1.000000` and the empty band.
+
+- `[measurepin-probe]` (stderr, `UDPSCOPE_PROBE_MEASUREPIN_MS`) — **what window a measurement
+  describes**: on a still frame the pane is about the *frame*, so a pan or a zoom changes no
+  number, and on a live view the numbers still follow the window. Three legs — a latched event, a
+  pause taken from it, and a live view after the trigger is switched off — each read the pane
+  before and after a *gesture* written on the row's own axis (never the window control, which
+  calls off the pin). The assertions, in order: the pinned legs read **`same=4/4 for_same=1
+  pass_delta=0`** with `for=` still at the pin (the values bit-identical and no recompute spent on
+  the gesture), and the live leg reads **`follows=1`** with `for_same=0`, `pass_delta>0` and the
+  results window's span narrowed to the axis'. Its sequence is about 12 s, so
+  `UDPSCOPE_EXIT_AFTER_MS=20000`; run it on the fast mock with a batch the datagram limit allows
+  (`--rate 1300000 --batch 1500 --freq 1`, **not** `--batch 2000`, which is 80 kB of payload and
+  dies with `Message too long`). The lines, the fields and the settle wait are in
+  [probe-readings.md](probe-readings.md); the window rule itself is in
+  [invariants-measurements.md](invariants-measurements.md).
+
 - `[pan-probe] asked=[..] was=[..]`, `[pan-probe] after=[..] held=D asked=[..]`, then
   `[pan-probe] zoom asked=[..] after=[..] span=S window=W limited=L`
   (stderr, `UDPSCOPE_PROBE_PAN_MS`) — **`held` must be 1**: a gesture must not move a window
@@ -124,7 +364,7 @@ precedent, not an exception.
   *tick*, one frame after the ask: a `g_timeout` was the first version and it drifted past the
   paused/resumed boundary under load. The probe then asks for a **zoom-out** ten times the current span and reports
   the span the next frame produced: **`limited` must be 1**, i.e. `span <= window`. Run it with
-  a ring that holds *more* than the window (`--buffer-mb 64` past the window's own seconds) —
+  a ring that holds *more* than the window (`--buffer-samples 2M` past the window's own seconds) —
   that is the state the old `max(retained, window_s_)` bound leaked in, and it showed up here as
   `span=2.502550 window=2.000000 limited=0` against `span=2.000000` after the fix.
 
@@ -191,8 +431,8 @@ precedent, not an exception.
   nothing. Its four lines are in
   [probe-readings.md](probe-readings.md).
 - `UDPSCOPE_EXPORT_MS` (+ optional `UDPSCOPE_EXPORT_PATH`, default
-  `/tmp/udpscope-export`) — collect the export table and write it both ways, skipping
-  only the file chooser.
+  `/tmp/udpscope-export`) — collect the export table and write it all three ways (`.npy`,
+  `.csv`, `.mf3`), skipping only the file chooser.
 
 - `UDPSCOPE_PROBE_CONDITION_MS` — arms a qualified trigger against the mock and reports the latched
   `t0`, the measured pulse or band width, and sample values for the window condition. Schedules its
@@ -205,6 +445,139 @@ precedent, not an exception.
   pauses, reports again with `dn=` per measurement, then resets and reports a third time. Three
   phases: `phase=0`, `phase=1` (after pause) and `phase=2` (after Reset). Needs
   `UDPSCOPE_ENABLE_ALL_MS` ahead of it and `UDPSCOPE_PROBE_MEASURE_MS` to add measurements first.
+- `UDPSCOPE_PROBE_SIDE_TAB_MS=3000` with `UDPSCOPE_EXIT_AFTER_MS=11000` — the measurements while the
+  `measure` page is **closed**: it adds four measurements, opens the page for a forced pass (the baseline),
+  closes it, and reads the accumulators again two seconds later. **`advanced=<rows>` is the assertion**
+  (every accumulator gained passes while the page was off screen); `advanced=0` is the defect where the
+  accumulation is gated on what is visible, which would leave a gap in min/max/avg for exactly as long as the
+  page was shut. It enables *and plots* its own signal, so it needs no other probe ahead of it, and it
+  re-arms once after 400 ms (a buffer rebuild between baseline and report reads as a gated pass). It needs a
+  config that has seen the first-run tour, which would close the page it opens (see the next-but-one bullet).
+  The reading's own entry is in `probe-readings.md`. (Probe name `dock_section_probe`; the variable and the
+  `[side-tab-probe]` tag keep their old names so existing scripts keep working. The measurements used to be a
+  dock section the probe scrolled out of view, with padding; the dock now holds the readouts and the Events block, so there is
+  no scroll and no padding.)
+- `UDPSCOPE_PROBE_CURSORS_MS` and `UDPSCOPE_PROBE_MEASURES_MS` also print the dock's copy of what they read:
+  a `dock cursors:` line after every `[cursors-probe]` report and a `dock measures:` line at the
+  measures probe's added / settled / final stops, each with a `strip:` line beside it (the readouts strip,
+  shown when `(!dock_shown || collapsed)` and the cursors are on or there is a measurement; `expected=` is that, `visible_ok=1` that the strip agrees, `groups=`/`groups_ok=1` the same for its Cursors / Measures groups and separator; the measures probe's `start` line, before it adds anything, is the hidden "neither" state -- run it from a fresh config); each probe
+  ends by hiding the dock for 0.6 s and reading the strip (`dock hidden`, `dock restored`: under xvfb the
+  window is collapsed, so `visible=1 expected=1 h=26 same_text=1` on both, given something to read). **`same_text=1` on every one** is the assertion that the
+  dock, the strip and the page show one string; `fits=1` that the Readouts box is no wider than the dock. Entries in
+  `probe-readings.md`. The exit chain also prints one `[readouts]` line (pages registered, the dock page's three
+  children, the dock's width, the pages' sensitivity, whether the stream has signals) on every exit-dump run.
+- `UDPSCOPE_PROBE_DOCK_SESSION_MS=2500` with `UDPSCOPE_EXIT_AFTER_MS=8000` -- the session file's `dock` key,
+  end to end: the dock hidden, saved and reloaded; shown again; and a file from the previous version
+  (`side_tab = "measure"`, no `dock`) loaded without an error. Three `[dock-session]` lines, each `ok=1`;
+  entries in `probe-readings.md`.
+- `UDPSCOPE_PROBE_SLIDEOVER_MS=1500` with `UDPSCOPE_EXIT_AFTER_MS=5000` (and `UDPSCOPE_ENABLE_ALL_MS=500`) -- the
+  slide-over panel over the plot's right edge, opened on a throw-away `probe` page, read 0.5 s later. Two
+  `[slideover]` lines. Line 1 must read `panel=360x<overlay height> ... edge_flush=1 full_height=1
+  outside_hits_plot=1 inside_hits_panel=1 ... plot_unchanged=1`: a 360 px opaque panel flush to the overlay's
+  right edge and as tall as it, a pick outside it landing in the plot and one inside it in the panel, and the
+  plot's width unchanged by the panel being open (`plot_w before=` equal to `open=`).
+  `outside_hits_plot=0` means the panel has an allocation wider than 360 or a transparent parent that
+  swallows the plot's pan, drop and hover; `plot_unchanged=0` means the panel resized the plot. Line 2 must
+  read `click_inside_closes=0 still_open=1 click_outside_closes=1 esc_closes=1 closed=1`. For a screenshot
+  add `UDPSCOPE_PROBE_SLIDEOVER_HOLD=1`, which leaves the page open after line 1 (run with `GSK_RENDERER=cairo`
+  and `import -window root`): the panel must be drawn over the traces, opaque.
+- **Slide-over and page probes (`SLIDEOVER`, `BADGES`, `SIGNAL_PAGES`, `SIGNAL_BADGES`, `SIDE_TAB`, `KEYS`) need a config that has already seen
+  the first-run tour**: a fresh `XDG_CONFIG_HOME` auto-starts the tour at about 1.5 s, and a tour stop with no page closes the
+  slide-over under the probe. Seed it with `mkdir -p $D/udpscope && printf 'tour_seen = true\n' > $D/udpscope/settings.toml`
+  (or one short throw-away run, which writes the key when the tour starts) and run with `XDG_CONFIG_HOME=$D`. Delete the
+  per-source subdirectory (`$D/udpscope/<host>_<port>`) between runs that must start from a first-run layout.
+- `UDPSCOPE_PROBE_SIGNAL_PAGES_MS=1500` with `UDPSCOPE_EXIT_AFTER_MS=5000` and `UDPSCOPE_ENABLE_ALL_MS=500` -- the
+  per-signal `signal:<name>` slide-over pages. **Against a config that has already seen the tour** (a first run's
+  auto-tour closes the slide-over at about 1.5 s, which is when this probe opens its page). One `[signalpage]` line;
+  see [probe-readings.md](probe-readings.md).
+- `UDPSCOPE_PROBE_SIGNAL_BADGES_MS=1500` with `UDPSCOPE_EXIT_AFTER_MS=5000` and `UDPSCOPE_ENABLE_ALL_MS=500` -- the
+  signal badges in the badge bar. **Against a config that has already seen the tour**, as above (the probe clicks
+  the badges, and the auto-tour would close the page). One `[sigbadges]` line; see
+  [probe-readings.md](probe-readings.md).
+- `UDPSCOPE_PROBE_BADGES_MS=2000` with `UDPSCOPE_EXIT_AFTER_MS=5000` and `UDPSCOPE_ENABLE_ALL_MS=500` -- the badge
+  bar under the plot. One `[badges]` line, which must read `table_bad=0 fixed=1 open_marked=1 page_open=1
+  closed_unmarked=1`: `table_bad` counts the rows of the 16-input `trigger_badge_state()` table the probe
+  gets wrong; `fixed=1` is the bar's height being the same (and at least 36 px) before and after the
+  `trigger` page was opened and closed -- `0` means the bar's height depends on content and the plot above it
+  moves; `open_marked`/`closed_unmarked` are the `udpscope-badge-open` class following the slide-over's page.
+  `trigger_state=` is the state word as read then (`off` with the trigger toggle off). **The trigger form is
+  a slide-over page**, so a probe that reads one of its widgets' *allocation* (a width, a height) must
+  `slideover_open(*a, "trigger")` and read after the 120 ms reveal, as `exit_probe_step1` and `force_probe` do;
+  a sensitivity, a visibility or a value needs no open page.
+  **The source kind's panels are slide-over pages too** (`source-<id>`: the E-1608's `source-ao` and
+  `source-dio`, Flat UDP's, the probe kind's), so the same rule holds for them. The probe appends a second
+  `[badges]` line for the Source badge: `[badges] source name=<kind> pages=<n>
+  visible=<0|1> switch_visible=<0|1> can_target=<0|1> second_page=<id|-> second_ok=<0|1> open_marked=<0|1|-1>
+  closed_unmarked=1`. `pages` is the number of source pages, `switch_visible` is the segmented switch
+  being on screen after the first source page was opened (`1` for the E-1608's two pages, `0` for one page
+  or none), `second_page` is what `slideover_page()` read after the switch selected the second page
+  (`second_ok=1` when it is that page), `visible=0` with `pages=0` is the UDPS badge being **hidden** (a kind with no source page
+  has nothing for it to open; `can_target=0` goes with it) and `open_marked=-1` is that no-page case (there is
+  nothing to open); `visible=1` with `pages>0`.
+- `UDPSCOPE_PROBE_SOURCE_KINDS=2000` with `UDPSCOPE_EXIT_AFTER_MS=5000`, run as `--source probe --source-opt rate=500`
+  -- the source-plugin path end to end. The variable's presence also registers the test-only `probe` kind (a
+  synthetic sine with one panel), so it is the only way a run sees that kind; its value is the delay in ms.
+  Nine `[source-kinds]` lines (one `form` line per registered kind: `udps`, `e1608`, `flatudp`, `probe`); the
+  reading's own entry is in `probe-readings.md`.
+- `UDPSCOPE_PROBE_E1608=1500` with `UDPSCOPE_EXIT_AFTER_MS`, run as `--source e1608` against
+  `tools/mock_e1608.py` -- the MCC E-1608 end to end: panels present and sensitive, a DAC write, a
+  digital-output toggle and a counter reset each reaching the mock, the stream's channels and rate, the
+  factory calibration applied, the capture button disabled, and a hand-computed decode. It enables the
+  signals itself, so do **not** add `UDPSCOPE_ENABLE_ALL_MS` (that probe switches the first signal off
+  after two seconds). Three runs, each short and serial, with the mock killed afterwards:
+  - **no board:** panels `sensitive=0`, `connected=0`, no retry flood on stderr (the one
+    `[e1608] handshake with ...: Connection refused` line is printed once, not per retry);
+  - **the mock:** `--drop-after 3 --log /tmp/e1608-mock.log`, options `scan_rate=1000 ai0=BIP10V
+    ai1=BIP5V plot0=1 plot_counter=1 dir1=o ao0_init=1.5`, with `UDPSCOPE_PROBE_E1608=1500
+    UDPSCOPE_PROBE_E1608_RECONNECT=8000 UDPSCOPE_EXIT_AFTER_MS=10500`; then read the mock's log: the AO
+    levels `1.5, 2.5, 1.5` (the log prints the quantised voltage, so `1.4999, 2.4999, 1.4999` is the
+    expected text), the DOUT bytes `0x00, 0x02, 0x00`, one `COUNTER_RESET`, one `DROP`;
+  - **a rejected code:** mock `--code 1234`, app `code=7`: one error line, the retries stop.
+- `UDPSCOPE_PROBE_E1608_GEN=1500` with `UDPSCOPE_EXIT_AFTER_MS=5500`, run as `--source e1608 --source-opt
+  address=127.0.0.1 --source-opt port=54711 --source-opt ao0_init=0 --source-opt gen_rate=100` against
+  `tools/mock_e1608.py --port 54711 --log /tmp/e1608-gen100.log` -- the generator's update rate: it starts a Sine
+  on DAC 0 through the Analog out panel (and opens the `source-ao` slide-over page, since the panel refreshes on
+  its frame clock, which does not tick for a page that is off screen; the page is closed again at the end),
+  waits 2.5 s, reads the achieved rate and the panel's "Update rate" row, stops the generator and reads both
+  again 400 ms later. Two lines, in `probe-readings.md`. Then count the mock log's `AOUT` lines: about 250 with
+  `gen_rate=100` (the generator ran for about 2.5 s) and about 125 for a run without the option (default
+  50 Hz). Short and serial, the mock killed afterwards. It enables nothing else, so it can run alone.
+- `UDPSCOPE_PROBE_E1608_RECONNECT=8000` -- reads the source after the mock dropped the link and 500 ms
+  later checks the frame count moved on. The reading's own entry is in `probe-readings.md`.
+- `UDPSCOPE_PROBE_E1608_SCAN=1000` with `UDPSCOPE_EXIT_AFTER_MS=6500`, run as `--source e1608 --source-opt
+  address=127.0.0.1`. Start `tools/mock_e1608.py` first on its default port 54211 (the form scans that port; do
+  not pass `--port`) and kill it afterwards. The value is the delay of phase 1; phase 2 follows 2 s after it and
+  phase 3 (the line) 2 s after that, so phase 3 runs 4 s after phase 1 and the delay must stay below about
+  2500 ms for the line to print before the exit at 6500 ms. It builds
+  the connection form, presses **Scan network**, expects the mock to be listed, clicks the result (address
+  filled, MAC and subnet cleared), presses **Use MAC** (MAC filled, the others cleared), scans again and checks
+  the results were replaced. `UDPSCOPE_PROBE_E1608_SCAN_MAC` names another board (a real one) instead of the
+  mock's `00:80:2f:00:16:08`. One `[e1608] scan:` line. It needs a non-loopback up interface with a broadcast
+  address; when the board did not answer a second line says so, and the run proves nothing about the scan.
+- `UDPSCOPE_PROBE_FLATUDP=2500` with `UDPSCOPE_EXIT_AFTER_MS`, run as `--source flatudp` against
+  `tools/mock_flatudp.py` -- the flat UDP source end to end: a hand-computed codec and decode check and the connect form's validity rules and signal-row editor (both
+  need no source; it covers the `w` suffix, the waveform and 256-channel rules, the channel decode and the
+  float64/uint16/int32/uint32/int64 types in both byte orders), the stream's channel names (`Wave[0]`..
+  for a `channels` vector) and declared rates (`rate * count` for a waveform), the channel count, value
+  continuity per row (and the offset between a vector's elements, or a waveform's block phase), the
+  wrong-size accounting and the capture button. It enables the signals itself, so do **not** add
+  `UDPSCOPE_ENABLE_ALL_MS`. Runs, each short and serial, with the mock killed afterwards (quote the `signals`
+  value: zsh globs the `[4]`):
+  - **mixed list, gap and bad datagrams:** mock `--rate 1000 --signals 'Trigger:uint8,Ia:float32,Cnt:uint64,Wave:int16[4]'
+    --gap 8,4 --bad-every 1` started 1 s before the app, the same `signals` as a `--source-opt`, with
+    `UDPSCOPE_PROBE_FLATUDP=2500 UDPSCOPE_PROBE_FLATUDP_GAP=1500 UDPSCOPE_EXIT_AFTER_MS=14500`; stderr carries
+    exactly one `datagram of 22 bytes, expected 21` line. The silence probe is a 100 ms poll that waits for the
+    stream, then for the 2 s of silence to take the source down, then for it to come back, so it does not
+    depend on when `xvfb-run` finished starting; the only requirement is that the mock's gap begins after
+    the app connected (the mock's clock starts about 4 s before the app's) and ends in time to read the return
+    (`--gap 8,4` with a 14.5 s run does both with several seconds of margin);
+  - **waveform-only list:** mock `--signals 'Wave:int16[4]w'`, app `--source-opt 'signals=Wave:int16[4]w'`,
+    `UDPSCOPE_PROBE_FLATUDP=2500 UDPSCOPE_EXIT_AFTER_MS=5000`: one channel at `rate=4000`;
+  - **big endian (decode of every width through the stream):** mock `--big-endian` on the mixed list, app
+    `--source-opt endian=big`, `UDPSCOPE_PROBE_FLATUDP=2500 UDPSCOPE_EXIT_AFTER_MS=5000`;
+  - **no sender:** `connected=0` throughout, a reading and not a failure.
+- `UDPSCOPE_PROBE_FLATUDP_GAP=1500` -- starts the silence poll described above (2 s after the source's last
+  datagram it must be disconnected; then it must reconnect and the frame count move on).
 - `UDPSCOPE_PROBE_SEARCH_MS` — runs a buffer search for the armed condition, cross-checks the live
   trigger's own `t0` against the nearest hit (`agree=1` is the load-bearing reading), and jumps to
   hit 0. Reports the resulting `mode=`, `axis=` and `marks placed=`.
@@ -224,9 +597,14 @@ as distinct from the fault injection below, which exercises ingest:
   conditions for the first four: the mock at `--rate 10000 --batch 100 --freq 5`, udpscope with
   no extra options, under `xvfb-run` with
   `UDPSCOPE_EXIT_AFTER_MS=8000 UDPSCOPE_ENABLE_ALL_MS=600 UDPSCOPE_EXIT_DUMP=1
-  UDPSCOPE_PROBE_RESEQ_MS=5000`. Delete `~/.config/udpscope/127.0.0.1_8000.toml` first: a
-  session left by an earlier run restores its math channel, and five channels instead of four
-  change `channels=`, `span=` and every count derived from them.
+  UDPSCOPE_PROBE_RESEQ_MS=5000`. Move `~/.config/udpscope/127.0.0.1_8000/` aside first (the
+  per-endpoint session is a *directory* now -- `active` plus one `.toml` per named configuration;
+  a bare `127.0.0.1_8000.toml` is a pre-migration leftover): a session left by an earlier run
+  restores its math channel, and five channels instead of four change `channels=`, `span=` and
+  every count derived from them. It restores the **window and the measurements** too, which is
+  the subtler trap: a run after a zoom-sweep probe starts at `window_s = 0.05` with the previous
+  runs' measurements still in the pane, so `measures window:` then reports a short-window
+  sawtooth (144 %, marks off screen) on a run that asked for none of it.
 
   | case | mock extra flags | key reading |
   | --- | --- | --- |
@@ -269,11 +647,19 @@ as distinct from the fault injection below, which exercises ingest:
   and **`finite=0` beside a non-zero `hole_slots` is the defect** (a biquad that integrated the
   hole's NaN, permanently). The filters' `sd` must stay near the no-drop value; run the same
   command without `--drop-every` as the control, where every `finite` reads 4000.
+- **A math edit on a ring that has already wrapped.** `UDPSCOPE_PROBE_MATHWRAP_MS` — installs one
+  `Gain` graph over the mock's sine, waits for the ring to **saturate**, and only then edits the gain,
+  which is the one state `UDPSCOPE_PROBE_MATH_MS` cannot reach (each of its edits follows a structural
+  change, and a replan restarts every ring at absolute 0). It therefore needs a **small buffer and a long
+  run**: `--buffer-samples 65536` against `--rate 20000 --batch 200`, with
+  `UDPSCOPE_PROBE_MATHWRAP_MS=1500 UDPSCOPE_EXIT_AFTER_MS=25000`. `base > 0` on its second line is the
+  precondition — **`base=0` means the run tested nothing** — and the third line's `produced == slots` and
+  `y=±0.5` are the two assertions; both are in [probe-readings.md](probe-readings.md).
 - `UDPSCOPE_PROBE_CONFIGS_MS` — saves the running session as a configuration named `probe` with a
   note, through `save_configuration_as()` (the same entry point the dialog's button uses), then
   reads it back off disk. Reading: `save-as=1`; `names=` gains `probe`; `active=probe`; and the
   round trip must carry the note **and** the startup settings —
-  `comment='written by the configs probe' buffer_mb=8 relative=0 capture=0`. A `buffer_mb=0` there
+  `comment='written by the configs probe' buffer_samples=10000000 relative=0 capture=0`. A `buffer_samples=0` there
   is the per-source buffer size not being written, which is the one setting a user notices only
   after a capture has been sized wrong. Run it with a throwaway `XDG_CONFIG_HOME`; the probe
   deletes its own configuration at the end (`after forget names=…`).
@@ -293,6 +679,34 @@ as distinct from the fault injection below, which exercises ingest:
   `GtkMenuButton`-owned submenu failed, its row going dead on the second click. Each view is
   measured a step after the click that swapped it in, because a popover allocates its new child on
   the next layout pass.
+- `UDPSCOPE_PROBE_HELPUI_MS` — the help affordance layer, end to end, in ten steps 300–400 ms apart:
+  the **first-run auto-start** (run it once with a throwaway `XDG_CONFIG_HOME` to see `auto=1`, and
+  again against the same one to see it not repeat), the menu's seven rows and the **four entries of
+  the Help submenu**, the **contextual-help toggle** with the count of "(i)" affordances on either side
+  of it, the tour **started from the probe** and stepped forwards, back and dismissed, and `help
+  figures:` read in both of the trigger pane's modes. Its lines and what each asserts are in
+  [probe-readings.md](probe-readings.md); the two things to read first are **`hints=0`** while the
+  toggle is off (off is *gone*, not greyed) and **`controllers=12 (was 12)`** after the dismissal (no
+  lingering input grab — a tour of ordinary overlay widgets takes none), and **`hint=12x12`** is the
+  size the shrunk "(i)" must keep (the default menu-button mark is 34x34). The `collapsed search:` line
+  is the header hint read on the search block's expander while it is collapsed. The chooser's own tour is
+  the other half and has its own entry points — see the **chooser** bullet below. Give it
+  `UDPSCOPE_EXIT_AFTER_MS=9500 UDPSCOPE_EXIT_DUMP=1` to get the `help layer:`/`help figures:` dump
+  lines as well, and note the tour **auto-starts** in any run whose settings file does not carry
+  `tour_seen` — **in the source chooser when there is one**, in the window otherwise (see the chooser
+  bullet) — so a probe run against a fresh config directory will have it on screen for the first
+  second and a half, and that start *writes* `tour_seen` to whichever config directory the run is
+  using, which is why the second run against the same one reads `auto=0`.
+- `UDPSCOPE_PROBE_TOUR_SURFACE_MS` — the tour's *surface* switch: it opens a slide-over page (`trigger`),
+  starts the window's tour from that state and walks all six stops a stop per tick, reading the
+  slide-over's open page and the spotlight/card at each. The trigger stop must read `slideover=trigger` and
+  the next `slideover=none`; the first stop closes the panel the probe left open, and the end of the walk
+  (and a dismissal on the trigger stop) leave none. It then puts the dock *away* and starts the tour again:
+  the dock's stops are dropped while the trigger stop, which does not depend on the dock, stays.
+  `[toursurface] stop=3/6 … slideover=trigger … contains=1` and
+  `[toursurface] collapsed: side_box_mapped=0 steps=5 trigger_stop=1 signals_stop=1` are the assertions; its
+  lines are in [probe-readings.md](probe-readings.md). Run it alone with
+  `UDPSCOPE_EXIT_AFTER_MS=9000 UDPSCOPE_EXIT_DUMP=1` against a live source.
 - `UDPSCOPE_PROBE_DEFAULTS_MS` — opens **Calibrate** and reads every spin button in it and in the
   trigger panel: `[defaults] calibrate: 1 0 model=1 0 | trigger: 0.001 0.002 0 0.001 0 50 0.01`. A
   `GtkSpinButton` starts at its range's *minimum*, so a `-1e12` here is an unseeded button the
@@ -301,10 +715,26 @@ as distinct from the fault injection below, which exercises ingest:
   `[defaults] calibrated: 2.5 -1.25 model=2.5 -1.25` — **the dialog must show the signal's stored
   calibration**, and the two halves must match.
 - The **chooser**, display-free: `UDPSCOPE_PROBE_SOURCES=1` prints `[sources] N known:` with one
-  entry per configuration (`host:port/name … buffer= relative= note='…'`), and
+  entry per configuration (`host:port/name … samples= relative= note='…'`), and
   `UDPSCOPE_PROBE_PICK_MS=800` opens the chooser, picks the first row and prints
-  `[sources] picked host:port … buffer=64 relative=0 capture=0 config=… note='…'` — the settings the
-  configuration carried, into the `Config` the model is built from. A legacy file
+  `[sources] picked host:port … samples=2097152 relative=0 capture=0 config=… note='…'` — the settings the
+  configuration carried, into the `Config` the model is built from. **With no `--server` and no probe
+  the chooser blocks in its own nested loop** (no frame to end and no dump), so a chooser run is
+  always this probe. It also prints the dialog's frame *and its own help layer*:
+  `[sources] chooser ui: … hints=[2 {chooser_sources chooser_waveform}] hint=12x12` with the setting
+  on, `hints=[0 {}] hint=0x0` with it off. `UDPSCOPE_PROBE_CHOOSER_HELP=1` drives the **Enable
+  contextual help** row and reads the file back; `UDPSCOPE_PROBE_CHOOSER_TOUR=1` drives the **Guided
+  tour** row and walks the chooser's own tour to its last stop, printing `[sources] chooser tour: …`
+  and the handoff (`tour_pending=1`); `UDPSCOPE_PROBE_CHOOSER_TOUR_MS=<ms>` walks it a stop per tick
+  instead, printing the page the stack shows at every stop and stepping **Back** off the stop that
+  stands on the waveforms page — the reading for the surface a stop changes. It starts the walk
+  itself when one is not running, so it does not need a first-run config; pair it with
+  `UDPSCOPE_PROBE_PICK_MS` after the walk so the application's half follows. A working run: seed a
+  source once (`./build/udpscope --server 127.0.0.1 --port N` against a mock, under the throwaway
+  `XDG_CONFIG_HOME`), then run bare with
+  `UDPSCOPE_PROBE_CHOOSER_TOUR_MS=2000 UDPSCOPE_PROBE_PICK_MS=4500 UDPSCOPE_EXIT_AFTER_MS=12000
+  UDPSCOPE_EXIT_DUMP=1`. Its lines and what each asserts are in
+  [probe-readings.md](probe-readings.md). A legacy file
   (`<host>_<port>.toml`) produces `layout loaded from …/<host>_<port>/default.toml`, an `active`
   holding `default`, and the old file renamed `.imported`.
 - **The loading window covers the gap, and only on the path that asked.** The same
@@ -316,41 +746,50 @@ as distinct from the fault injection below, which exercises ingest:
   leg of it (`title='Opening <basename>' detail='reading the recording'`, before `waveform loaded:`).
   A run that names its source with `--server` prints **no** `loading:` line at all: every other probe
   here is on that path and must stay on it.
-- **The event cache round-trips, and only where it is available.** `UDPSCOPE_PROBE_EVENTS_MS` reads
-  the pane's availability first, in the state the app starts in -- `[events] live: button_visible=0
-  pane=0 recording=1`, **no pane and no button without trigger mode** -- then turns trigger mode on
-  through the real toggle (`[events] after trigger on: button_visible=1 pane=0`: the button appears,
-  the pane stays collapsed) and clicks the button, waits for a latch, then reads the cache and replays
-  the newest event through the pane's own row:
+- **The event cache round-trips, and only where it is available.** `UDPSCOPE_PROBE_EVENTS_MS` needs a
+  config that has seen the tour (it opens a slide-over page) and a throwaway `XDG_CACHE_HOME`. It reads the
+  availability first, in the state the app starts in -- `[events] live, recording off: available=0
+  dock_sensitive=0 page_sensitive=0 page=none` (the dock block and the page agree, both insensitive and neither
+  hidden) -- then switches recording on (`available=1 dock_sensitive=1 page_sensitive=1`; **trigger mode is not
+  a condition**, and the line after the trigger is turned on reads the same), opens the `events` page with
+  `open_events_page()` (`page=events`, `[events] open alone: page=events page_box=347`), waits for a latch, then
+  reads the cache and replays the newest event through the page's own row:
   `[events] dir=… n=1 newest: dur=2.000000 pre=1.000000 post=1.000000 edge=… signals=4 samples=20001
-  rate=10000 seq=1 thumb_bytes=230454 recorded=1 pane=1`, then
-  `[events] activated row0: replaying=1 thumbnail=1 thumb_size=108x36 thumb_visible=1` (the size is
-  what says the picture is *on screen*: a paint-able alone is not), `[events] replayed: channels=4
-  samples=20001 replaying=1 waveform=1` and `[events] live again: replaying=0 waveform=0`. It ends on
-  the pane's availability, through the trigger panel's switch: `[events] recording off, trigger off` and
-  `[events] recording off, trigger on` -- once the cache holds events (the probe's own run has written
-  some by this point) both read `button_visible=1 pane=1 recording=0`, because a button that shows the
-  cache must not go away with the switch that wrote it; against an *empty* cache the same two lines read
-  `button_visible=0 pane=0`, which is the empty column the item exists to prevent. **`samples` must equal the
-  export's row count for the same window** (`20001` for a 2 s event at 10 kS/s), `thumb_bytes` must be
-  a real BMP (`54 + 480*160*3`-ish, i.e. hundreds of kB, not 0), `thumbnail` must be 1 (the row loaded
-  the picture) and the last line must read `replaying=0` -- a replay with no way back is a one-way
+  rate=10000 seq=1 thumb_bytes=230454 recorded=1 page=1 plot_w_stable=1 plot_w=756/756` (**`plot_w_stable=1`**: the
+  first latch did not move the plot, which the old pane did), then
+  `[events] activated row0: replaying=1 page=events … thumbnail=1 thumb_size=138x46 thumb_visible=1` (the size is
+  what says the picture is *on screen*: a paint-able alone is not), the dock's reading of the same cache --
+  `[events] dock events: rows=N pane_rows=N same_titles=1 sensitive=1 dock_w=268 on_screen=1 … at=after pane
+  replay` -- then **one click on a dock row**, `[events] dock replay: clicked=1 replaying=1 waveform_changed=1`,
+  and the dock read again (`marked=1`, `expected_marked=1`: exactly one filled marker, on the replayed record),
+  `[events] replayed: channels=4 samples=20001 replaying=1 waveform=1` and `[events] live again: replaying=0
+  waveform=0`. It ends on the availability, through the trigger panel's switch: `[events] recording off,
+  trigger off` and `[events] recording off, trigger on` -- once the cache holds events (the probe's own run has
+  written some by this point) both read `available=1 dock_sensitive=1 page_sensitive=1`, because a block that
+  shows the cache must not go away with the switch that wrote it; against an *empty* cache (and on the E-1608,
+  which never latches) the same two lines read `0 0 0` with the page still open -- insensitive, never hidden.
+  **`samples` must equal the export's row count for the same window** (`20001` for a 2 s event at 10 kS/s),
+  `thumb_bytes` must be a real BMP (`54 + 480*160*3`-ish, i.e. hundreds of kB, not 0), `thumbnail` must be 1 (the
+  row loaded the picture) and the last line must read `replaying=0` -- a replay with no way back is a one-way
   door. It then **waits for a second latch** (bounded: twelve retries) and drives the two group layouts
   through the buttons: `[events] compare buttons: cached=2 selected=2 compare=1 accumulate=1` (the
   buttons read the selection), `[events] halve`… `[events] halves a_first=20001 a_second=0 b_first=0
   b_second=20001` -- **the two halves of the ring, and the reading that says a comparison's gap is a
   gap: the first event's channel is finite only in the first half and the second's only in the second**
   -- `[events] compare: kind=1 rows=4 channels=8 samples0=40002 traces0=2 traces1=2 window=4.000
-  recording=1 pane=1` (`samples0` must be exactly the stamps pushed, **not more**: a live producer left
-  running pushes its own four signals into the group's eight channels), `[events] compare plots:
+  recording=1 page=events` (`samples0` must be exactly the stamps pushed, **not more**: a live producer left
+  running pushes its own four signals into the group's eight channels), the dock line `members=2 … at=comparison
+  up` (the hollow markers on the group's members, which only the dock shows), `[events] compare plots:
   area_b=1 rows_a=1 rows_b=1 x_a=[-2.000,0.000] x_b=[-2.000,0.000] same_x=1` (the second plot exists, is
   on screen, mirrors the row count, and both are on one x window), then the sync -- the probe sets a y
   range nobody would arrive at by accident on the *first* plot and reads the second a few frames later:
   `[events] compare sync: y_a=-3.500 y_b=-3.500 mirrored=1` -- and `[events] accumulate: kind=2 rows=1
   channels=8 samples0=33045 selected=2 traces0=8 window=2.000` (`traces0=8`: the four signals the layout
   holds plus one layer each for the second event, **in the same row**, which is what an accumulation
-  means). Run it with a throwaway
-  `XDG_CACHE_HOME` and `UDPSCOPE_EXIT_AFTER_MS` long enough for the second latch (20 s).
+  means). The exit dump adds `events pane: compare=1 accumulate=1 list=1 nested=1` and the readouts line's
+  `dock_children=3`. Run it with a throwaway
+  `XDG_CACHE_HOME` and `UDPSCOPE_EXIT_AFTER_MS` long enough for the second latch (20 s). The dock row cap
+  (24) is only exercised by a cache that has filled past it: `max_ok=1`.
 - **A waveform round-trips.** Export from a live run (`UDPSCOPE_EXPORT_MS` with
   `UDPSCOPE_EXPORT_PATH`, against the mock at 10 kS/s), then open that file with `--open` and an
   exit dump. The load must print
@@ -368,7 +807,7 @@ as distinct from the fault injection below, which exercises ingest:
   python3 -c "import numpy as np; n=1000000; t=-4.0+np.arange(n)/50000.0; \
   a=np.zeros(n, dtype=[('time','<f8'),('abs_seconds','<f8'),('a','<f4'),('b','<f4'),('c','<f4'),('d','<f4')]); \
   a['time']=t; a['abs_seconds']=1000.0+t; a['d']=np.linspace(-1,1,n); np.save('/tmp/long.npy', a)"
-  xvfb-run -a env UDPSCOPE_EXIT_AFTER_MS=4000 ./build/udpscope --open /tmp/long.npy --buffer-mb 1
+  xvfb-run -a env UDPSCOPE_EXIT_AFTER_MS=4000 ./build/udpscope --open /tmp/long.npy --buffer-samples 32768
   ```
   must read `samples=31250 rows=1000000 decim=32 span=19.999980s time=[-4.000000..15.999980]` and
   `stored=31250 … published=31250` per channel — **the whole span, at a thirty-second of the rate**.
@@ -401,21 +840,21 @@ as distinct from the fault injection below, which exercises ingest:
   the field the file dialog's callback sets and prints `[sources] picked waveform <path>` — then the
   load line above, with no socket involved.
 - **A `--server` launch reads the stored configuration.** With a throwaway `XDG_CONFIG_HOME`
-  holding `127.0.0.1_8101/bench.toml` (`buffer_mb = 64`, `relative_time = true`,
+  holding `127.0.0.1_8101/bench.toml` (`buffer_samples = 2097152`, `relative_time = true`,
   `capture_packets = 500`, `active` = `bench`), `./build/udpscope --server 127.0.0.1 --port 8101`
-  must print `[sources] settings from configuration 'bench': buffer=64 relative=1 capture=500`, the
-  `relative time:` line, and a `span=` of about 209 s (64 MB at 10 kS/s) — **not** the 200 MB
-  default's ~655 s. The same command with `--buffer-mb 8` must read `buffer=8` and `span=26.214s`:
+  must print `[sources] settings from configuration 'bench': samples=2097152 relative=1 capture=500`, the
+  `relative time:` line, and a `span=` of about 209 s (2 097 152 ticks at 10 kS/s) — **not** the 10M default's ~839 s. The same command with
+  `--buffer-samples 262144` must read `samples=262144` and `span=26.214s`:
   **an explicit flag wins over the file**. Without this, the settings a host was edited to have were
   ignored whenever the address came from the command line.
 - The chooser's **form**, with `UDPSCOPE_PROBE_PICK_MS` scheduling it:
   `UDPSCOPE_PROBE_NEWHOST=host:port` fills it and prints
-  `[sources] form: name='probe-host' note='…' buffer=32 relative=1 connect_sensitive=1`, then
-  `[sources] configuration created: host:port/probe-host … buffer=32 relative=1` and a
+  `[sources] form: name='probe-host' note='…' samples_m=0.5 relative=1 connect_sensitive=1`, then
+  `[sources] configuration created: host:port/probe-host … samples=500000 relative=1` and a
   `picked … config=probe-host`; a following `UDPSCOPE_PROBE_SOURCES=1` must list it
-  (`buffer=32 relative=1 note='…'`) — a configuration the form wrote that the chooser does not
+  (`samples=500000 relative=1 note='…'`) — a configuration the form wrote that the chooser does not
   list cannot be edited next time. `UDPSCOPE_PROBE_EDITHOST=host:port` opens the same form on that
-  configuration and prints `[sources] edit form: name='…' note='…' buffer=… relative=… button='Save'`
+  configuration and prints `[sources] edit form: name='…' note='…' samples_m=… relative=… button='Save'`
   — **the pre-fill is the assertion**: an edit form that opens empty cannot edit anything — then
   saves and reports the new values. `UDPSCOPE_PROBE_EDITNAME=new-name` renames it as well: one
   `known:` row afterwards, with the old file gone.
@@ -489,7 +928,7 @@ as distinct from the fault injection below, which exercises ingest:
   at 64. The `mixed` case's `open_holes=43` against `bands=43` has no such spread because
   nothing re-planned. The per-field reference is in [probe-readings.md](probe-readings.md).
 
-The mock also carries three **fault injections** that no probe schedules, because what they exercise
+The mock also carries four **fault injections** that no probe schedules, because what they exercise
 is the ingest rather than the UI. The first: `--time-glitch-at <stream seconds> --time-glitch-by <seconds>` makes
 **one** packet's time signal jump ahead and then carries on from where the true timeline was, which
 is what a device whose clock glitches puts on the wire. Run it with the trigger armed, e.g.
@@ -514,7 +953,7 @@ Four readings, all off the once-a-second `[udpscope] trig engine:` line:
 Before the fix the same run read a fallback warning, `history` collapsing 4.03 → 0.95, `now_t`
 jumping 5.040 → 16.040, and two latches **1.2 s** apart. Note the window here comes from the saved
 session for that port; the figures above are the default 2 s window (50 % pre), so move
-`~/.config/udpscope/<host>_<port>.toml` aside to reproduce them.
+`~/.config/udpscope/<host>_<port>/` aside to reproduce them.
 
 The other two are **packet loss** (`--drop-every N`, `--drop-burst K`) and **wire inversion**
 (`--reorder-every N`). Loss withholds a datagram the counter and the stream clock have already
@@ -524,6 +963,41 @@ arrives within the 20 ms reorder window is resequenced with no hole, and one tha
 leaves a committed hole that it then backfills (`UDPSCOPE_PROBE_RESEQ_MS` exercises both paths).
 There is **no interpolation** anywhere below the ring.
 
+The fourth is the counter itself: **`--counter-step N`** advances the header counter by `N` per
+datagram instead of one -- a device whose counter counts *samples*, or frames of an inner layer,
+rather than packets. Nothing is withheld and every datagram goes out on schedule, so the link is
+intact and the status bar is right to say `live`; what is wrong is the counter's claim, which the
+client cannot check (it has no clock) and only the app can (it has the arrival times). It is the
+one wire shape the mock could not otherwise produce, and the run that reads it is the reseq probe
+with relative time on (the mode that frames a counter gap as NaN by construction):
+
+```sh
+# mock: --counter-step 10
+xvfb-run -a env UDPSCOPE_EXIT_AFTER_MS=8000 UDPSCOPE_ENABLE_ALL_MS=600 \
+  UDPSCOPE_PROBE_RESEQ_MS=5000 UDPSCOPE_EXIT_DUMP=1 \
+  ./build/udpscope --server 127.0.0.1 --port 8000 --relative-time
+```
+
+```
+# fixed:  [reseq-probe] … holes=1 hole_slots=900 backfilled=0 gaps_refused=419 open_holes=0
+#         bands=0 bands_repaired=0 nan_slots=0 scanned=21700 trigger_in_hole=0
+#         status bar: glance=[● live · 9.97 kS/s · 2 s window]
+# broken: [reseq-probe] … holes=420 hole_slots=378000 backfilled=0 open_holes=64 bands=64
+#         bands_repaired=0 nan_slots=198000 scanned=220000 trigger_in_hole=0
+#         status bar: glance=[● live · 101 kS/s · 2 s window]
+```
+
+**`gaps_refused` above 0 with `nan_slots` at 0 is the assertion** — the gap was refused and the
+samples were kept. The broken reading is `nan_slots` at 90% of `scanned` with `backfilled=0`: a
+reserved hole per datagram, `relative_time` framing each one as NaN, and nothing ever missing to
+backfill it, i.e. one missing-data band over the whole window with no trace in it, under a status
+bar reading `live` at ten times the stream's real rate. The same field
+must be **0** on every honest shape above (`--drop-every`, `--drop-burst 200`,
+`--reorder-delay-ms 50`, at 10 kS/s: `holes=210 hole_slots=21000 nan_slots=11000 scanned=22000
+gaps_refused=0` for `--drop-every 2`, `holes=3 hole_slots=60000 nan_slots=20000` for the 200-packet
+burst at 100 kS/s) — a non-zero reading there means the arrival test is refusing real loss, whose
+only cost is a gap with no shading.
+
 All of the readings below are off `UDPSCOPE_EXIT_DUMP`'s `[udpscope] frames= packets= gaps=` line,
 over an 8 s run against `--rate 10000 --batch 100 --freq 5` (100 packets a second) except where the
 burst needs the faster stream. **`gaps` is the exact reading** and repeats to the packet; `frames`
@@ -576,13 +1050,24 @@ same run).
 ```bash
 cd /home/martino/Projects/tools/udpscope
 python3 tools/mock_udpstreamer.py --port 8108 --rate 1300000 --batch 1000 --duration 20 \
-  --spike-every 0.005 --spike-amp 0.5 --spike-width 2 > /tmp/noise-mock.log 2>&1 &
+  --spike-every 0.005 --spike-amp 0.5 --spike-width 2 --square-harmonics 0 \
+  > /tmp/noise-mock.log 2>&1 &
 sleep 1.5
 xvfb-run -a env UDPSCOPE_EXIT_AFTER_MS=18000 UDPSCOPE_ENABLE_ALL_MS=1000 \
   UDPSCOPE_PROBE_NOISE_MS=4000 \
   ./build/udpscope --server 127.0.0.1 --port 8108 2>&1 | grep -E 'noise-probe|CRITICAL'
 ```
 
+`--square-harmonics 0` is the one flag in that command that is not about the sine, and it is what keeps the
+probe's last reading exact: the group-delay leg measures a one-pole's *step* response on `square`, and the
+mock's square rings by default (see [build-and-run.md](build-and-run.md)). A band-limited edge moves that
+crossing off `tau*ln2` — measured `delay=0.002770 ratio=1.255` against the ideal step's `0.002206 / 1.000`,
+and the same figure on every run, so it is a property of the shape and not of the run. The leg's assertion is
+the `0.7..1.4` band, which the ripple keeps, but the ideal step is what keeps the *number* the line prints
+beside `want` as well. The other legs measure event counts on the sine, which the ripple does not touch; the
+counts do read a few percent lower under the ripple at this rate, for the producer-cost reason
+[build-and-run.md](build-and-run.md) gives.
+
 `UDPSCOPE_PROBE_NOISE_MS` is **not the time its readings are taken**. It times the probe's first stage, which
 installs a math graph through `apply_math_channels()` -- and that is a *structural rebuild* that replaces the
 buffer and drops its history. Every reading the probe takes is over retained history, so the rebuild has to
@@ -594,8 +1079,9 @@ stages into one is the failure mode**: a probe that rebuilt the buffer at 11.5 s
 immediately would read `bare=0` on every search leg, which looks exactly like a broken comparator.
 
 **Why 4 s and not 3.** `enable_all_probe`'s last act is a timeout of its own, `ENABLE_ALL_MS + 2000` -- 3 s
-under this recipe -- which walks `signal_list` for the front channel's acquire tick and clicks it. A probe
-that installs a math graph at that same instant rebuilds the signal panel under it, and the off-step then
+under this recipe -- which opens the front channel's signal page and clicks its "Acquire this signal" tick (an
+acquired signal is not in the Add-a-signal list, so the list cannot be walked). A probe
+that installs a math graph at that same instant rebuilds the signal panels under it, and the off-step then
 emits `active` on a freed `GtkCheckButton`: `GLib-GObject-CRITICAL: instance with invalid (NULL) class
 pointer`, with the backtrace in `enable_all_probe()::{lambda}`. It is a real fragility of that probe's lookup
 and not of the feature, and it is why every documented probe time is offset from `ENABLE_ALL_MS + 2000`, not
@@ -611,8 +1097,11 @@ have run. `--spike-every`/`--spike-amp`/
 
 The three lines and what each must read are in `probe-readings.md`.
 
-`UDPSCOPE_PROBE_NOISE_MS`, `UDPSCOPE_PROBE_MEASURE_MS` and `UDPSCOPE_PROBE_MATH_MS` must **not** be scheduled
-in the same run. The noise and measurement probes both push onto `app.measures`, and the later one would read
-the earlier one's rows as its own; the noise and math probes both write `app.math`, so the later one's graph
+`UDPSCOPE_PROBE_NOISE_MS`, `UDPSCOPE_PROBE_MEASURE_MS`, `UDPSCOPE_PROBE_MEASURES_MS`,
+`UDPSCOPE_PROBE_BANDAVG_MS`, `UDPSCOPE_PROBE_MATH_MS` and `UDPSCOPE_PROBE_MATHWRAP_MS` must **not** be
+scheduled in the same run. The noise, measurement, measurements and band-average probes all push onto
+`app.measures`, and the later one would read
+the earlier one's rows as its own; the noise, math and math-wrap probes all write `app.math`, so the later
+one's graph
 lands on top of the earlier one's and both sets of readings describe a state neither probe set up. The noise probe carries
 its own measurement legs (see `probe-readings.md`), so nothing is lost by keeping them apart.

docs/superpowers/plans/2026-11-02-e1608-network-scan.md

@@ -0,0 +1,681 @@
+# E-1608 Network Scan Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** The E-1608 connection form gets a "Scan network" row that finds boards on every local interface and fills the address or the MAC from a click; the MAC lookup in `E1608Source` stops depending on the default route.
+
+**Architecture:** A non-blocking `Scan` class in `e1608_link` opens one UDP socket per up IPv4 broadcast interface (bound to the device, or to its address), sends `D` on each and drains replies on `poll()`. The form drives it with a 50 ms GLib timer on the GTK main thread (the project has exactly two threads, so no worker). `discover_broadcast()` is `Scan` plus a blocking wait and replaces the limited-broadcast `discover()` call in the source's MAC lookup.
+
+**Tech Stack:** C++20, GTK4/libadwaita (`AdwExpanderRow`, `AdwActionRow`), POSIX sockets (`getifaddrs`, `SO_BINDTODEVICE`), `tools/mock_e1608.py`, the in-app headless probe under `xvfb-run`.
+
+## Global Constraints
+
+- Spec: `docs/superpowers/specs/2026-11-02-e1608-network-scan-design.md` (approved 2026-11-02).
+- Exactly two threads: no worker thread for the scan; the form polls with `g_timeout_add*`.
+- Every source file carries the SPDX MIT header (no new source files in this plan).
+- Text buttons only (no theme icons) on the new controls.
+- A `subnet` that is given still uses `sweep_targets` + `discover` unchanged.
+- An interface that cannot be opened or sent on is skipped, never an error; no interfaces is an empty result.
+- Scan results are never persisted: the session reads and writes only the filled fields.
+- Baselines: a clean build has exactly 3 warnings (an incremental build shows the 2 `ui_probe.cpp` MathNode ones); `gtk warnings: 0`; no `Gtk-CRITICAL`.
+- GTK traps (`docs/claude/invariants-gtk-and-chrome.md`): handler signatures are notify `(GObject*, GParamSpec*, gpointer)`, clicked `(GtkButton*, gpointer)`, changed `(GtkEditable*, gpointer)`; handlers behind `Form::alive`; probes use `g_object_ref_sink` + `g_object_unref` on never-parented rows.
+- Probe code must avoid `x({...}).empty() || y({...}).empty()` (GCC `-Wdangling-pointer`).
+- Verification runs are short and serial; kill every mock afterwards. Do not push or merge.
+
+## File Structure
+
+- Modify `src/source/e1608/e1608_link.hpp` / `.cpp`: `class Scan`, `discover_broadcast()`, a shared reply parser used by `discover()` too.
+- Modify `src/source/e1608/e1608_source.cpp`: the MAC lookup with an empty subnet uses `discover_broadcast()`.
+- Modify `src/source/e1608/e1608_kind.cpp`: the scan row, result rows, fills, timer.
+- Modify `src/ui_probe.cpp`, `src/ui_app.hpp`, `src/ui.cpp`: the `UDPSCOPE_PROBE_E1608_SCAN` probe.
+- Modify docs: `README.md`, `docs/claude/{build-and-run,verification,probe-readings,architecture}.md`.
+
+One design note the spec leaves open: `AdwExpanderRow` can only append rows, so "results right after the scan row" is done by making the scan row itself an `AdwExpanderRow` ("Scan network", a text "Scan" suffix button) at the top of the Connection expander, with the results as its child rows. It reads the same: results sit directly under the scan row.
+
+---
+
+### Task 1: The `Scan` class, `discover_broadcast()`, and the MAC lookup
+
+**Files:**
+- Modify: `src/source/e1608/e1608_link.hpp` (after `discover`, line ~77)
+- Modify: `src/source/e1608/e1608_link.cpp` (includes; anonymous namespace; `discover`; new definitions)
+- Modify: `src/source/e1608/e1608_source.cpp:270-293`
+
+**Interfaces:**
+- Produces (used by Task 2):
+  ```cpp
+  class Scan {
+   public:
+    explicit Scan(int port);
+    Scan(const Scan&) = delete;
+    Scan& operator=(const Scan&) = delete;
+    const std::vector<DeviceInfo>& poll();      // drains non-blocking; cumulative, one entry per MAC
+    std::size_t interfaces() const noexcept;    // sockets opened
+  };
+  std::vector<DeviceInfo> discover_broadcast(int port, int wait_ms);
+  ```
+- Consumes: existing `Fd`, `DeviceInfo`, `kProductId`, `Clock`, `ms_left`.
+
+- [ ] **Step 1: Declare the API**
+
+In `e1608_link.hpp`, after the `discover` declaration add:
+
+```cpp
+/// A broadcast discovery that never blocks. The limited broadcast alone leaves through the default
+/// route only, so on a host with several interfaces it can miss a board on another one; this opens
+/// one socket per up, non-loopback IPv4 interface with a broadcast address (bound to the device, or
+/// to the interface address when binding to the device is refused), sends `D` to
+/// 255.255.255.255 on each, and collects the replies as `poll()` is called. The caller owns the
+/// clock. An interface that cannot be opened or sent on is skipped; no interface is an empty scan.
+class Scan {
+ public:
+  explicit Scan(int port);
+  Scan(const Scan&) = delete;
+  Scan& operator=(const Scan&) = delete;
+  /// Drains every socket without blocking. The devices found so far: E-1608s only, one per MAC.
+  const std::vector<DeviceInfo>& poll();
+  /// How many interfaces a probe was sent on.
+  std::size_t interfaces() const noexcept { return socks_.size(); }
+
+ private:
+  std::vector<Fd> socks_;
+  std::vector<DeviceInfo> found_;
+};
+
+/// `Scan` plus a blocking wait of `wait_ms`: what a lookup by MAC with no subnet uses.
+std::vector<DeviceInfo> discover_broadcast(int port, int wait_ms);
+```
+
+- [ ] **Step 2: Share the reply parser**
+
+In `e1608_link.cpp` add includes `#include <ifaddrs.h>`, `#include <net/if.h>`, `#include <thread>` (keep the list alphabetical with the existing ones). Inside the existing anonymous namespace, just before its closing `}  // namespace` (after `tcp_connect`), add:
+
+```cpp
+/// A `D` reply (at least 29 bytes, first byte `D`, our product id). True when it added a board
+/// that `found` did not already hold (one entry per MAC).
+bool take_reply(const std::uint8_t* buf, ssize_t n, const sockaddr_in& from,
+                std::vector<DeviceInfo>& found) {
+  if (n < 29 || buf[0] != 'D') return false;
+  DeviceInfo info;
+  info.product_id = static_cast<std::uint16_t>(buf[7] | (buf[8] << 8));
+  if (info.product_id != kProductId) return false;
+  std::copy(buf + 1, buf + 7, info.mac.begin());
+  for (const DeviceInfo& d : found) {
+    if (d.mac == info.mac) return false;
+  }
+  char ip[INET_ADDRSTRLEN] = {};
+  ::inet_ntop(AF_INET, &from.sin_addr, ip, sizeof ip);
+  info.ip = ip;
+  found.push_back(info);
+  return true;
+}
+```
+
+In `discover()`, replace the block from `if (n < 29 || buf[0] != 'D') continue;` through `found.push_back(info);` (the lines that build `info`, test the MAC for a duplicate and push) with the single call:
+
+```cpp
+    take_reply(buf, n, from, found);
+```
+
+- [ ] **Step 3: Implement `Scan` and `discover_broadcast`**
+
+After `discover()` (before the `// --- Link` banner) add:
+
+```cpp
+Scan::Scan(int port) {
+  ifaddrs* list = nullptr;
+  if (::getifaddrs(&list) != 0) return;
+  sockaddr_in to{};
+  to.sin_family = AF_INET;
+  to.sin_port = htons(static_cast<std::uint16_t>(port));
+  to.sin_addr.s_addr = htonl(INADDR_BROADCAST);
+  const std::uint8_t probe = 'D';
+  std::vector<std::string> done;  // an interface with several addresses needs one probe, not several
+  for (const ifaddrs* a = list; a != nullptr; a = a->ifa_next) {
+    if (a->ifa_addr == nullptr || a->ifa_addr->sa_family != AF_INET) continue;
+    const unsigned fl = a->ifa_flags;
+    if ((fl & IFF_UP) == 0 || (fl & IFF_LOOPBACK) != 0 || (fl & IFF_BROADCAST) == 0) continue;
+    const std::string name = a->ifa_name;
+    if (std::find(done.begin(), done.end(), name) != done.end()) continue;
+    Fd s(::socket(AF_INET, SOCK_DGRAM | SOCK_NONBLOCK, 0));
+    if (!s.valid()) continue;
+    const int one = 1;
+    ::setsockopt(s.get(), SOL_SOCKET, SO_BROADCAST, &one, sizeof one);
+    if (::setsockopt(s.get(), SOL_SOCKET, SO_BINDTODEVICE, name.c_str(),
+                     static_cast<socklen_t>(name.size())) != 0) {
+      sockaddr_in me = *reinterpret_cast<const sockaddr_in*>(a->ifa_addr);
+      me.sin_port = 0;
+      if (::bind(s.get(), reinterpret_cast<const sockaddr*>(&me), sizeof me) != 0) continue;
+    }
+    if (::sendto(s.get(), &probe, 1, MSG_NOSIGNAL, reinterpret_cast<const sockaddr*>(&to),
+                 sizeof to) != 1)
+      continue;
+    done.push_back(name);
+    socks_.push_back(std::move(s));
+  }
+  ::freeifaddrs(list);
+}
+
+const std::vector<DeviceInfo>& Scan::poll() {
+  for (const Fd& s : socks_) {
+    for (;;) {
+      std::uint8_t buf[128];
+      sockaddr_in from{};
+      socklen_t flen = sizeof from;
+      const ssize_t n = ::recvfrom(s.get(), buf, sizeof buf, MSG_DONTWAIT,
+                                   reinterpret_cast<sockaddr*>(&from), &flen);
+      if (n < 0) break;  // nothing more on this socket for now
+      take_reply(buf, n, from, found_);
+    }
+  }
+  return found_;
+}
+
+std::vector<DeviceInfo> discover_broadcast(int port, int wait_ms) {
+  Scan scan(port);
+  const auto deadline = Clock::now() + std::chrono::milliseconds(wait_ms);
+  while (ms_left(deadline) > 0) {
+    scan.poll();
+    std::this_thread::sleep_for(std::chrono::milliseconds(10));
+  }
+  return scan.poll();
+}
+```
+
+- [ ] **Step 4: Use it in the source's lookup**
+
+In `e1608_source.cpp` `connect_and_start()`, replace
+
+```cpp
+    const std::vector<std::string> targets =
+        host.empty() ? sweep_targets(cfg_.subnet) : std::vector<std::string>{host};
+    const std::vector<DeviceInfo> found =
+        discover(targets, cfg_.port, std::min(cfg_.timeout_ms, 1500));
+```
+
+with
+
+```cpp
+    const std::vector<std::string> targets =
+        host.empty() ? sweep_targets(cfg_.subnet) : std::vector<std::string>{host};
+    const int wait_ms = std::min(cfg_.timeout_ms, 1500);
+    // No address and no subnet: the limited broadcast, sent on every interface rather than only
+    // the default route's.
+    const bool broadcast =
+        host.empty() && targets.size() == 1 && targets[0] == "255.255.255.255";
+    const std::vector<DeviceInfo> found =
+        broadcast ? discover_broadcast(cfg_.port, wait_ms) : discover(targets, cfg_.port, wait_ms);
+```
+
+- [ ] **Step 5: Build**
+
+Run: `cmake --build build -j8 2>&1 | grep -E "warning:|error:" ; echo done`
+Expected: no `error:`; only the 2 baseline `ui_probe.cpp` MathNode warnings (incremental) -- nothing new from `e1608_link.cpp` or `e1608_source.cpp`.
+
+- [ ] **Step 6: Verify the MAC lookup end to end against the mock**
+
+The mock answers a broadcast `D` on UDP 54211. A run with only a `mac` option (no address, no subnet) must find it and stream:
+
+```sh
+python3 tools/mock_e1608.py --port 54211 > /tmp/mock-scan.log 2>&1 &
+MOCK=$!
+UDPSCOPE_PROBE_E1608=1500 UDPSCOPE_EXIT_AFTER_MS=4000 xvfb-run -a ./build/udpscope --source e1608 \
+  --source-opt mac=00:80:2f:00:16:08 --source-opt scan_rate=1000 2>&1 | grep -E "^\[e1608\] (stream|state)"
+kill $MOCK
+```
+
+Expected: `[e1608] stream: connected=1 ... ok=1` and `state: connects=1 message=''`.
+If it reads `connected=0` with `no E-1608 with MAC ... answered`: the sandbox did not loop the broadcast back to the mock. Check with `ip -4 -o addr` that an up non-loopback interface with a broadcast address exists. If one does and it still fails, report that to the user as a finding; do not paper over it.
+
+- [ ] **Step 7: Commit**
+
+```bash
+git add src/source/e1608/e1608_link.hpp src/source/e1608/e1608_link.cpp src/source/e1608/e1608_source.cpp
+git commit -m "e1608: discover boards on every interface, not only the default route's"
+```
+
+---
+
+### Task 2: The form's "Scan network" row, results and fills
+
+**Files:**
+- Modify: `src/source/e1608/e1608_kind.cpp`
+
+**Interfaces:**
+- Consumes: `Scan`, `DeviceInfo`, `format_mac` (Task 1 / existing, via `e1608_source.hpp`'s includes of `e1608_link.hpp`; add the include if the build says otherwise).
+- Produces (used by Task 3's probe), by widget name: the scan row `AdwExpanderRow` named `e1608-scan-row`; its suffix `GtkButton` named `e1608-scan`; each result an `AdwActionRow` named `e1608-result` (title IP, subtitle MAC, `activated` fills the address) holding a suffix button named `e1608-use-mac`. Subtitle texts: `Scanning...`, `1 board found`, `N boards found`, `No board found`.
+
+- [ ] **Step 1: Add the state and `fill()` to `Form`**
+
+In `struct Form`, after `bool alive = true;...` add:
+
+```cpp
+  GtkWidget* scan_row = nullptr;       ///< the "Scan network" expander; the results are its rows
+  std::vector<GtkWidget*> results;     ///< the result rows of the current scan
+  std::unique_ptr<Scan> scan;          ///< non-null while a scan is running
+  guint timer = 0;                     ///< the GLib source polling `scan`, 0 when none
+  int scan_ms = 0;                     ///< time spent in the running scan
+```
+
+and, after `write(...)`:
+
+```cpp
+  /// A result click: puts one way of naming the board in and the other two fields out, under the
+  /// `updating` guard so the dialog is told once.
+  void fill(const std::string& addr, const std::string& mac_text) {
+    if (!alive) return;
+    updating = true;
+    gtk_editable_set_text(GTK_EDITABLE(address), addr.c_str());
+    gtk_editable_set_text(GTK_EDITABLE(mac), mac_text.c_str());
+    gtk_editable_set_text(GTK_EDITABLE(subnet), "");
+    updating = false;
+    if (changed && *changed) (*changed)();
+  }
+
+  void stop_scan() {
+    if (timer != 0) g_source_remove(timer);
+    timer = 0;
+    scan.reset();
+  }
+```
+
+Add `#include <vector>` to the includes if absent.
+
+- [ ] **Step 2: Destroy hook stops the timer**
+
+Replace `on_form_destroy` with:
+
+```cpp
+void on_form_destroy(GtkWidget*, gpointer user) {
+  Form& f = **static_cast<FormPtr*>(user);
+  f.alive = false;
+  f.stop_scan();  // the poll must not outlive the rows it writes to
+}
+```
+
+- [ ] **Step 3: The scan functions**
+
+After `hook_entry(...)` and before `class E1608Kind`, add:
+
+```cpp
+constexpr int kScanMs = 1500;  ///< how long a scan listens
+constexpr int kTickMs = 50;    ///< how often it drains the sockets
+
+/// A result row's two ways to name the board, with the form they fill.
+struct Pick {
+  FormPtr form;
+  std::string ip, mac;
+};
+
+void free_pick(gpointer d, GClosure*) { delete static_cast<Pick*>(d); }
+
+void on_pick_address(AdwActionRow*, gpointer user) {
+  Pick& p = *static_cast<Pick*>(user);
+  p.form->fill(p.ip, "");
+}
+
+void on_pick_mac(GtkButton*, gpointer user) {
+  Pick& p = *static_cast<Pick*>(user);
+  p.form->fill("", p.mac);
+}
+
+void add_result(const FormPtr& f, const DeviceInfo& d) {
+  const std::string mac = format_mac(d.mac);
+  GtkWidget* row = adw_action_row_new();
+  gtk_widget_set_name(row, "e1608-result");
+  adw_preferences_row_set_title(ADW_PREFERENCES_ROW(row), d.ip.c_str());
+  adw_action_row_set_subtitle(ADW_ACTION_ROW(row), mac.c_str());
+  gtk_list_box_row_set_activatable(GTK_LIST_BOX_ROW(row), TRUE);
+  GtkWidget* use_mac = gtk_button_new_with_label("Use MAC");
+  gtk_widget_set_name(use_mac, "e1608-use-mac");
+  gtk_widget_set_valign(use_mac, GTK_ALIGN_CENTER);
+  adw_action_row_add_suffix(ADW_ACTION_ROW(row), use_mac);
+  g_signal_connect_data(row, "activated", G_CALLBACK(on_pick_address),
+                        new Pick{f, d.ip, mac}, free_pick, static_cast<GConnectFlags>(0));
+  g_signal_connect_data(use_mac, "clicked", G_CALLBACK(on_pick_mac), new Pick{f, d.ip, mac},
+                        free_pick, static_cast<GConnectFlags>(0));
+  adw_expander_row_add_row(ADW_EXPANDER_ROW(f->scan_row), row);
+  adw_expander_row_set_expanded(ADW_EXPANDER_ROW(f->scan_row), TRUE);
+  f->results.push_back(row);
+}
+
+void set_scan_status(Form& f, const std::string& text) {
+  adw_expander_row_set_subtitle(ADW_EXPANDER_ROW(f.scan_row), text.c_str());
+}
+
+/// 50 ms poll of the running scan. The rows appear as boards answer; at `kScanMs` the status is
+/// settled and the scan (its sockets) is released.
+gboolean on_scan_tick(gpointer user) {
+  const FormPtr& fp = *static_cast<FormPtr*>(user);
+  Form& f = *fp;
+  if (!f.alive || !f.scan) {
+    f.timer = 0;
+    return G_SOURCE_REMOVE;
+  }
+  const std::vector<DeviceInfo> found = f.scan->poll();
+  while (f.results.size() < found.size()) add_result(fp, found[f.results.size()]);
+  f.scan_ms += kTickMs;
+  if (f.scan_ms < kScanMs) return G_SOURCE_CONTINUE;
+  if (found.empty())
+    set_scan_status(f, "No board found");
+  else if (found.size() == 1)
+    set_scan_status(f, "1 board found");
+  else
+    set_scan_status(f, std::to_string(found.size()) + " boards found");
+  f.scan.reset();
+  f.timer = 0;
+  return G_SOURCE_REMOVE;
+}
+
+void free_form_ptr(gpointer d) { delete static_cast<FormPtr*>(d); }
+
+/// A new scan on the Port field's value: the previous results go, a running scan is replaced.
+void start_scan(const FormPtr& fp) {
+  Form& f = *fp;
+  if (!f.alive) return;
+  f.stop_scan();
+  for (GtkWidget* r : f.results) adw_expander_row_remove(ADW_EXPANDER_ROW(f.scan_row), r);
+  f.results.clear();
+  adw_expander_row_set_expanded(ADW_EXPANDER_ROW(f.scan_row), FALSE);
+  f.scan = std::make_unique<Scan>(static_cast<int>(value_of(f.port)));
+  f.scan_ms = 0;
+  set_scan_status(f, "Scanning...");
+  f.timer = g_timeout_add_full(G_PRIORITY_DEFAULT, kTickMs, on_scan_tick, new FormPtr(fp),
+                               free_form_ptr);
+}
+
+void on_scan_clicked(GtkButton*, gpointer user) {
+  start_scan(*static_cast<FormPtr*>(user));
+}
+```
+
+(`f.stop_scan()` removes the timer; `g_source_remove` fires `free_form_ptr`, which only drops one `FormPtr` copy, never the last. `on_scan_tick` never calls `g_source_remove` on itself: it zeroes `timer` and returns `G_SOURCE_REMOVE`.)
+
+- [ ] **Step 4: Build the row in `make_config_form()`**
+
+After the `f->ao_init[1] = ...` line, add:
+
+```cpp
+    f->scan_row = adw_expander_row_new();
+    gtk_widget_set_name(f->scan_row, "e1608-scan-row");
+    adw_preferences_row_set_title(ADW_PREFERENCES_ROW(f->scan_row), "Scan network");
+    GtkWidget* scan_button = gtk_button_new_with_label("Scan");
+    gtk_widget_set_name(scan_button, "e1608-scan");
+    gtk_widget_set_valign(scan_button, GTK_ALIGN_CENTER);
+    adw_expander_row_add_suffix(ADW_EXPANDER_ROW(f->scan_row), scan_button);
+    g_signal_connect_data(scan_button, "clicked", G_CALLBACK(on_scan_clicked), new FormPtr(f),
+                          free_form, static_cast<GConnectFlags>(0));
+```
+
+Change the Connection group to start with the scan row:
+
+```cpp
+    GtkWidget* conn = expander("Connection", {f->scan_row, f->address, f->mac, f->subnet, f->port,
+                                              f->code, f->timeout});
+```
+
+Update the description string to:
+
+```cpp
+    out.description =
+        "Give an address, or a MAC address to look up (optionally with a subnet such as 192.168.1), "
+        "or scan the network for boards";
+```
+
+- [ ] **Step 5: Build, then check the existing form round trip and warnings**
+
+```sh
+cmake --build build -j8 2>&1 | grep -E "warning:|error:" ; echo done
+UDPSCOPE_PROBE_SOURCE_KINDS=1000 UDPSCOPE_EXIT_AFTER_MS=2500 xvfb-run -a ./build/udpscope \
+  --source probe --source-opt rate=500 2>&1 | grep -E "form e1608|gtk warnings|Gtk-CRITICAL"
+```
+
+Expected: no `error:`, only the 2 baseline warnings; `[source-kinds] form e1608: round_trip=1 valid=1`; `gtk warnings: 0`; no `Gtk-CRITICAL`.
+
+- [ ] **Step 6: Commit**
+
+```bash
+git add src/source/e1608/e1608_kind.cpp
+git commit -m "e1608: a Scan network row in the connection form, with click-to-fill results"
+```
+
+---
+
+### Task 3: The scan probe, docs, and final verification
+
+**Files:**
+- Modify: `src/ui_probe.cpp` (after `e1608_probe_reconnect`, ~line 2459)
+- Modify: `src/ui_app.hpp:1874-1875`
+- Modify: `src/ui.cpp:6031-6033`
+- Modify: `README.md` (E-1608 paragraph, lines ~118-146), `docs/claude/build-and-run.md:118-130`, `docs/claude/verification.md` (after the `UDPSCOPE_PROBE_E1608_RECONNECT` bullet, ~line 443), `docs/claude/probe-readings.md` (`## [e1608]` section, ~line 1848-1890), `docs/claude/architecture.md:45-48`
+
+**Interfaces:**
+- Consumes: the widget names from Task 2; `find_named()`, `find_kind()` in `ui_probe.cpp`.
+- Produces: env var `UDPSCOPE_PROBE_E1608_SCAN=<ms>` and optional `UDPSCOPE_PROBE_E1608_SCAN_MAC` (default `00:80:2f:00:16:08`, the mock's); one stderr line `[e1608] scan: ...`.
+
+- [ ] **Step 1: Declare and register the probe**
+
+In `ui_app.hpp`, after `gboolean e1608_probe_resumed(gpointer user);` add:
+
+```cpp
+/// The E-1608 form's "Scan network" row: presses Scan against the mock, then (phases `_fill`,
+/// `_rescan`) clicks a result to fill the address, "Use MAC" to fill the MAC, scans again and checks
+/// the results were replaced, not added to.
+gboolean e1608_scan_probe(gpointer user);
+gboolean e1608_scan_probe_fill(gpointer user);
+gboolean e1608_scan_probe_rescan(gpointer user);
+```
+
+In `ui.cpp`, after the `UDPSCOPE_PROBE_E1608_RECONNECT` block add:
+
+```cpp
+  if (const char* env = g_getenv("UDPSCOPE_PROBE_E1608_SCAN")) {
+    g_timeout_add(static_cast<guint>(std::atoi(env)), e1608_scan_probe, &app);
+  }
+```
+
+- [ ] **Step 2: Write the probe**
+
+In `ui_probe.cpp`, after `e1608_probe_reconnect`, add (this is outside the file's anonymous namespace, like its neighbours; the helpers it uses, `find_named` and `find_kind`, are visible):
+
+```cpp
+namespace {
+
+/// The scan probe's state, alive from phase 1 to phase 3.
+struct E1608ScanProbe {
+  ConfigForm form;
+  int changes = 0;          ///< how many times the form told the dialog it changed
+  std::string want_mac;     ///< the board the probe expects (the mock's by default)
+  std::string status;       ///< the scan row's subtitle, as read at the end of the first scan
+  std::string ip;           ///< the expected board's address, as listed
+  std::size_t first = 0;    ///< result rows after the first scan
+  bool listed = false;      ///< the expected board was among them
+  bool fill_addr = false;
+  bool fill_mac = false;
+};
+
+E1608ScanProbe* g_scan_probe = nullptr;
+
+void collect_named(GtkWidget* root, const char* name, std::vector<GtkWidget*>& out) {
+  if (root == nullptr) return;
+  if (std::strcmp(gtk_widget_get_name(root), name) == 0) out.push_back(root);
+  for (GtkWidget* c = gtk_widget_get_first_child(root); c != nullptr;
+       c = gtk_widget_get_next_sibling(c))
+    collect_named(c, name, out);
+}
+
+std::string scan_status(E1608ScanProbe& p) {
+  GtkWidget* row = find_named(p.form.rows[0], "e1608-scan-row");
+  const char* t = row != nullptr ? adw_expander_row_get_subtitle(ADW_EXPANDER_ROW(row)) : nullptr;
+  return t != nullptr ? t : "";
+}
+
+/// A form holding stale values in all three naming fields, so a fill is seen to clear the others.
+void scan_probe_stale(E1608ScanProbe& p) {
+  SourceConfig c;
+  c.set("address", "1.2.3.4");
+  c.set("mac", "aa:bb:cc:dd:ee:ff");
+  c.set("subnet", "10.0.0");
+  p.form.write(c);
+  p.changes = 0;
+}
+
+void scan_probe_click(E1608ScanProbe& p) {
+  GtkWidget* button = find_named(p.form.rows[0], "e1608-scan");
+  if (button != nullptr) g_signal_emit_by_name(button, "clicked");
+}
+
+void scan_probe_cleanup() {
+  if (g_scan_probe == nullptr) return;
+  for (GtkWidget* row : g_scan_probe->form.rows) {
+    g_object_ref_sink(row);
+    g_object_unref(row);
+  }
+  delete g_scan_probe;
+  g_scan_probe = nullptr;
+}
+
+}  // namespace
+
+/// Phase 3, 2 s after the second Scan: the results were replaced (same count), and the one line.
+gboolean e1608_scan_probe_rescan(gpointer user) {
+  App* a = static_cast<App*>(user);
+  if (a->window == nullptr || g_scan_probe == nullptr) return G_SOURCE_REMOVE;
+  E1608ScanProbe& p = *g_scan_probe;
+  std::vector<GtkWidget*> rows;
+  collect_named(p.form.rows[0], "e1608-result", rows);
+  const bool replaced = rows.size() == p.first;
+  const std::string status = scan_status(p);
+  const bool status_ok = status.find("found") != std::string::npos && status.rfind("No", 0) != 0;
+  const bool ok = p.listed && p.fill_addr && p.fill_mac && replaced && status_ok;
+  std::fprintf(stderr,
+               "[e1608] scan: found=%zu ip=%s mac=%s status='%s' fill_addr=%d fill_mac=%d "
+               "rescan_replaced=%d ok=%d\n",
+               p.first, p.ip.c_str(), p.want_mac.c_str(), p.status.c_str(), p.fill_addr ? 1 : 0,
+               p.fill_mac ? 1 : 0, replaced ? 1 : 0, ok ? 1 : 0);
+  if (!p.listed)
+    std::fprintf(stderr,
+                 "[e1608] scan: %s did not answer; no up broadcast interface reaches it, or the "
+                 "broadcast was refused (this run proves nothing about the scan)\n",
+                 p.want_mac.c_str());
+  std::fflush(stderr);
+  scan_probe_cleanup();
+  return G_SOURCE_REMOVE;
+}
+
+/// Phase 2, 2 s after the first Scan: the expected board is listed, a result click fills the address
+/// only, "Use MAC" fills the MAC only (each telling the dialog exactly once), then Scan again.
+gboolean e1608_scan_probe_fill(gpointer user) {
+  App* a = static_cast<App*>(user);
+  if (a->window == nullptr || g_scan_probe == nullptr) return G_SOURCE_REMOVE;
+  E1608ScanProbe& p = *g_scan_probe;
+  p.status = scan_status(p);
+  std::vector<GtkWidget*> rows;
+  collect_named(p.form.rows[0], "e1608-result", rows);
+  p.first = rows.size();
+  GtkWidget* mine = nullptr;
+  for (GtkWidget* r : rows) {
+    const char* sub = adw_action_row_get_subtitle(ADW_ACTION_ROW(r));
+    if (sub != nullptr && p.want_mac == sub) mine = r;
+  }
+  p.listed = mine != nullptr;
+  if (mine != nullptr) {
+    const char* title = adw_preferences_row_get_title(ADW_PREFERENCES_ROW(mine));
+    p.ip = title != nullptr ? title : "";
+
+    scan_probe_stale(p);
+    g_signal_emit_by_name(mine, "activated");
+    const SourceConfig by_addr = p.form.read();
+    p.fill_addr = by_addr.get("address") == p.ip && by_addr.get("mac").empty() &&
+                  by_addr.get("subnet").empty() && p.changes == 1;
+
+    scan_probe_stale(p);
+    GtkWidget* use = find_named(mine, "e1608-use-mac");
+    if (use != nullptr) g_signal_emit_by_name(use, "clicked");
+    const SourceConfig by_mac = p.form.read();
+    p.fill_mac = by_mac.get("mac") == p.want_mac && by_mac.get("address").empty() &&
+                 by_mac.get("subnet").empty() && p.changes == 1;
+  }
+  scan_probe_click(p);
+  g_timeout_add(2000, e1608_scan_probe_rescan, a);
+  return G_SOURCE_REMOVE;
+}
+
+/// Phase 1: the form, Scan pressed (the row must read `Scanning...` at once), phase 2 in 2 s.
+gboolean e1608_scan_probe(gpointer user) {
+  App* a = static_cast<App*>(user);
+  if (a->window == nullptr) return G_SOURCE_REMOVE;
+  SourceKind* k = find_kind("e1608");
+  if (k == nullptr) {
+    std::fprintf(stderr, "[e1608] scan: no e1608 kind\n");
+    return G_SOURCE_REMOVE;
+  }
+  g_scan_probe = new E1608ScanProbe;
+  E1608ScanProbe& p = *g_scan_probe;
+  p.form = k->make_config_form();
+  const char* env = g_getenv("UDPSCOPE_PROBE_E1608_SCAN_MAC");
+  p.want_mac = env != nullptr ? env : "00:80:2f:00:16:08";
+  p.form.on_change([]() {
+    if (g_scan_probe != nullptr) ++g_scan_probe->changes;
+  });
+  scan_probe_click(p);
+  const std::string now = scan_status(p);
+  if (now != "Scanning...")
+    std::fprintf(stderr, "[e1608] scan: status right after Scan reads '%s', expected 'Scanning...'\n",
+                 now.c_str());
+  g_timeout_add(2000, e1608_scan_probe_fill, a);
+  return G_SOURCE_REMOVE;
+}
+```
+
+Notes for the implementer: `SourceConfig::get` returns `std::string` (the existing probe calls `f.read().get("signals") == "..."`); `find_kind`, `SourceConfig` and `ConfigForm` are already used in this file. Do not write `x({...}).empty() || y({...}).empty()`.
+
+- [ ] **Step 3: Build and run against the mock**
+
+```sh
+cmake --build build -j8 2>&1 | grep -E "warning:|error:" ; echo done
+python3 tools/mock_e1608.py --port 54211 > /tmp/mock-scan.log 2>&1 &
+MOCK=$!
+UDPSCOPE_PROBE_E1608_SCAN=1000 UDPSCOPE_EXIT_AFTER_MS=6500 xvfb-run -a ./build/udpscope \
+  --source e1608 --source-opt address=127.0.0.1 --source-opt scan_rate=1000 2>&1 \
+  | grep -E "^\[e1608\] scan|gtk warnings|Gtk-CRITICAL"
+kill $MOCK
+```
+
+Expected: `[e1608] scan: found=1 ip=<a local address> mac=00:80:2f:00:16:08 status='1 board found' fill_addr=1 fill_mac=1 rescan_replaced=1 ok=1`; `gtk warnings: 0`; no `Gtk-CRITICAL`. `found=2` or more is fine if a real board is on the network (status then reads `N boards found`; the line still needs `ok=1`).
+If `ok=0` and the second line says the board did not answer, check Task 1 Step 6's loopback note, and tell the user honestly; do not mark this step passed.
+If a flag other than `listed` reads 0, debug that flag (the fill reads the form back; `changes` must be exactly 1 per fill).
+
+- [ ] **Step 4: Clean-build warning count**
+
+```sh
+rm -rf /tmp/scan-clean && cmake -S . -B /tmp/scan-clean >/dev/null && cmake --build /tmp/scan-clean -j8 2>&1 | grep -c "warning:"; rm -rf /tmp/scan-clean
+```
+
+Expected: `3`.
+
+- [ ] **Step 5: Docs**
+
+- `README.md`, E-1608 paragraph (line ~119): after "...(optionally with the subnet to sweep)," add the scan: the sentence "A **Scan network** row at the top of the form probes every network interface of the host for boards (about a second and a half), lists each one by address and MAC, and a click on a result fills the address, or **Use MAC** fills the MAC and leaves the address empty. Results are not saved: only the filled field is." Also add one sentence that a MAC with no subnet is now looked up on every interface, not only the default route's, because a single limited broadcast leaves through the default route alone and missed a board on another interface (found on a real board 2026-11-02, where the board was on `net0` and the default route was `wlan0`).
+- `docs/claude/build-and-run.md` line ~125: change "a MAC with no `address` is looked up by broadcast" to "...looked up by a broadcast sent on every interface (`Scan`), or by a sweep of `subnet`".
+- `docs/claude/verification.md`: after the `UDPSCOPE_PROBE_E1608_RECONNECT=8000` bullet add a bullet for `UDPSCOPE_PROBE_E1608_SCAN=1000` with `UDPSCOPE_EXIT_AFTER_MS=6500`, run as `--source e1608 --source-opt address=127.0.0.1` against the mock on its default port 54211 (the form scans that port), optional `UDPSCOPE_PROBE_E1608_SCAN_MAC` for a real board; one `[e1608] scan:` line; note it needs a non-loopback up interface with a broadcast address, and that the line says so when the board did not answer.
+- `docs/claude/probe-readings.md`, `## [e1608]`: add the sample line `[e1608] scan: found=1 ip=172.21.121.113 mac=00:80:2f:00:16:08 status='1 board found' fill_addr=1 fill_mac=1 rescan_replaced=1 ok=1` to the block, and one bullet per field: `found` (result rows after the first scan; 0 with the "did not answer" second line is an environment without a reachable broadcast interface, not a pass), `status` (the row subtitle; "No board found" with a mock running is the probe sockets not reaching it), `fill_addr=0` (a result click did not set only the address, or told the dialog other than once), `fill_mac=0` (same for Use MAC), `rescan_replaced=0` (the results of the first scan were kept or doubled: `start_scan` did not remove them).
+- `docs/claude/architecture.md` line ~45: in the E-1608 three-layers bullet, add that discovery is `Scan` (one socket per interface, polled by the caller; the form polls it from a GLib timer on the main thread, the source's lookup through `discover_broadcast`).
+
+- [ ] **Step 6: Commit**
+
+```bash
+git add src/ui_probe.cpp src/ui_app.hpp src/ui.cpp README.md docs/claude
+git commit -m "e1608: probe and docs for the network scan"
+```
+
+- [ ] **Step 7: Manual run on the real board (only if it is attached)**
+
+Check `ip -4 -o addr` for the board's interface and `ping`-free: simply run the probe without the mock, naming the board's MAC (the user knows it; the MAC printed by the earlier hardware run was on `net0`, address 169.254.88.75):
+
+```sh
+UDPSCOPE_PROBE_E1608_SCAN=1000 UDPSCOPE_PROBE_E1608_SCAN_MAC=<board mac> UDPSCOPE_EXIT_AFTER_MS=6500 \
+  xvfb-run -a ./build/udpscope --source e1608 --source-opt address=127.0.0.1 2>&1 | grep -E "^\[e1608\] scan"
+```
+
+If it finds the board (`listed`, `ok=1`), add one sentence with the date to the README's E-1608 paragraph ("the network scan was checked against a real board on <date>") and commit `docs: record the scan check on a real board`. If the board is not attached or the MAC is unknown, say so; claim nothing.

docs/superpowers/plans/2026-11-02-ui-badges-dock-shell.md

@@ -0,0 +1,950 @@
+# Badge bar, slide-over and dock -- step 1 (the shell) Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Replace the sidebar's tab switcher with a plot-edge slide-over panel reached from a badge bar under the plot (Trigger and Source badges), keeping Measure and Signals reachable in a temporary always-on dock, so the app is usable after every task.
+
+**Architecture:** Two new units, `SlideOver` (`src/ui_slideover.cpp`, a `GtkRevealer` + `GtkStack` placed by margins as one opaque `GtkOverlay` child above the plot) and `BadgeBar` (`src/ui_badges.cpp`, a fixed-height row between the plot and the status line). The existing trigger form and the source kind's `SourcePanel` widgets are *reparented* into slide-over pages. The right `AdwOverlaySplitView` sidebar stays, but its `AdwViewSwitcher`/`AdwViewStack` become one scroller holding the signal list, the cursors and the measurements. The left events pane and everything else is untouched (spec step 4).
+
+**Tech Stack:** C++20, GTK4, libadwaita >= 1.8 (`AdwToggleGroup` is 1.7+), CMake. No unit-test suite: verification is the app's own headless self-check (`xvfb-run`, mock sources) -- extend `src/ui.cpp` / `src/ui_probe.cpp` probes, never a separate harness.
+
+Spec: `docs/superpowers/specs/2026-11-02-ui-badges-dock-design.md` (read it first). Branch: `feature/ui-badges-dock`.
+
+## Global Constraints
+
+Copied from the spec and the repository's rules; every task includes them.
+
+- **Layout must not depend on content** (`docs/claude/invariants-plot-and-layout.md`): the dock has a fixed width, the badge bar a fixed height, the slide-over overlays the plot and never resizes it. Rows that appear by trigger condition appear inside the slide-over's scroller.
+- **A `GtkOverlay` child is picked wherever its allocation is**: the slide-over is one opaque widget aligned to the end edge by `halign=END` and a 360 px width, never a full-area transparent child, so pan, drop and hover on the rest of the plot are untouched.
+- The header's Trigger / Cursors / Pause toggles keep their two-way mirroring with the panels.
+- `SourcePanel{id, title, widget}` is unchanged: the E-1608 and Flat UDP panels need no change.
+- Page ids: `trigger`, `signal:<name>`, `signals`, `measure`, `cursors`, `events`, `source-<id>`. (Step 1 implements `trigger` and `source-<id>` only.)
+- The open slide-over page is **not** saved. The session file drops `side_tab`; an old file's `side_tab` is ignored.
+- Esc or a click outside closes the slide-over; one page at a time; each page has its own scroller.
+- "Disable, do not hide": the dock is shown but insensitive until the stream has signals.
+- Text buttons only for new controls (no icon-only buttons, no icons in badges).
+- Every new source file carries the SPDX MIT header (`// SPDX-License-Identifier: MIT` / `// SPDX-FileCopyrightText: 2026 Martino Ferrari`).
+- Baselines: a clean build emits exactly **one** warning (the icons' `-Woverlength-strings`), an incremental build **zero**; the dump's `gtk warnings:` reads `0`; no `Gtk-CRITICAL`/`Gtk-WARNING`.
+- Verification runs are short and serial; kill every mock you start; do not re-run to chase cosmetics. Headless needs `GDK_BACKEND=x11` (the host has `WAYLAND_DISPLAY`) and, for screenshots, `GSK_RENDERER=cairo` + `import -window root`.
+- Do not push, merge or amend. Commit per task on `feature/ui-badges-dock`.
+
+## Deliberate step-1 deviations from the spec (state them in the final report)
+
+- The dock keeps the sidebar's **320 px** (spec: ~280). The panels it holds were built for 320; the width change belongs to step 3 when they become compact readouts.
+- The session file gains the dock's *shown* state only, not a width: the dock's width is fixed, so there is nothing to persist.
+- The Trigger badge shows `off / armed / triggered` plus `capturing` and `disarmed`, so the label never claims a state the engine is not in.
+
+## File Structure
+
+| File | Create/Modify | Responsibility |
+| --- | --- | --- |
+| `src/ui_slideover.cpp` | Create | The slide-over: build, page registry, open/close/toggle, Esc, click-away, `slideover` probe. |
+| `src/ui_badges.cpp` | Create | The badge bar: Trigger and Source badges, per-tick state, pure `trigger_badge_state()`, `badges` probe. |
+| `src/ui_app.hpp` | Modify | `SlideOver`/`BadgeBar` structs on `App`, declarations, removal of `side_stack`/`side_switcher`/`side_tab`/`keep_tabs_icon_free`. |
+| `src/ui/main-window.ui` | Modify | `plot_overlay` around `plot_box`; `badge_bar` row; the sidebar tab switcher/stack replaced by one dock scroller. |
+| `src/ui_widgets.cpp` | Modify | CSS for badges and the slide-over (`install_css`). |
+| `src/ui.cpp` | Modify | Build/wire both units in `on_activate`; tick sync; Esc; dock visibility; remove tab code. |
+| `src/ui_source.cpp` | Modify | Source panels become slide-over pages; `keep_tabs_icon_free` deleted. |
+| `src/ui_tour.cpp`, `src/ui_context_help.cpp` | Modify | Tour/context-help re-pointed (task 5). |
+| `src/ui_layout.cpp`, `src/layout_store.{hpp,cpp}` | Modify | `side_tab` out, `dock_shown` in. |
+| `src/shortcuts.{hpp,cpp}`, `src/ui/shortcuts.ui` | Modify | `SideTabMeasure/Signals` -> `ShowMeasure/ShowSignals`. |
+| `src/ui_probe.cpp` | Modify | New probes; every probe that touched the tab stack re-pointed. |
+| `CMakeLists.txt` | Modify | Add the two new `.cpp` files to the `udpscope` sources (next to `src/ui_source.cpp`). |
+| `README.md`, `docs/claude/*.md` | Modify | Task 6. (`USER-GUIDE.md` and the Mallard manual's figures are the spec's step 4.) |
+
+---
+
+### Task 1: SlideOver unit and the plot overlay (confirms the compositing risk)
+
+Spec step 1 says: confirm the overlay-above-GL risk *before* anything else is built on it. This task builds the slide-over with a throw-away probe page and proves composite, geometry and input.
+
+**Files:**
+- Create: `src/ui_slideover.cpp`
+- Modify: `src/ui/main-window.ui`, `src/ui_app.hpp`, `src/ui.cpp`, `src/ui_widgets.cpp`, `src/ui_probe.cpp` (or put the probe in `ui_slideover.cpp`; `ui_app.hpp` declares it either way), `CMakeLists.txt`, `docs/claude/verification.md` (probe env var line)
+
+**Interfaces:**
+- Produces (all in `namespace udpscope::ui_impl`, declared in `ui_app.hpp`):
+
+```cpp
+/// The slide-over panel's widgets and state (src/ui_slideover.cpp). `page` is the open page's id, empty when closed.
+struct SlideOver {
+  GtkWidget* overlay = nullptr;       ///< the GtkOverlay around the plot (main-window.ui `plot_overlay`)
+  GtkWidget* revealer = nullptr;      ///< the one overlay child; halign END, valign FILL, 360 px
+  GtkWidget* title = nullptr;         ///< GtkLabel in the panel header
+  GtkWidget* stack = nullptr;         ///< GtkStack: one scroller per page
+  GtkWidget* source_switch = nullptr; ///< AdwToggleGroup, shown on a source page when there are >= 2
+  std::vector<std::string> source_pages;
+  std::string page;
+  bool syncing = false;               ///< true while we write the toggle group ourselves
+};
+constexpr int kSlideOverWidth = 360;
+void build_slideover(App& app);                       // once, after the plot_overlay exists
+bool slideover_add_page(App& app, const std::string& id, const std::string& title, GtkWidget* content);
+bool slideover_has_page(const App& app, const std::string& id);
+bool slideover_open(App& app, const std::string& id); // false when the id is unknown
+void slideover_close(App& app);
+bool slideover_toggle(App& app, const std::string& id); // open if closed or on another page, else close; false if unknown
+const std::string& slideover_page(const App& app);    // "" when closed
+bool slideover_escape(App& app);                      // closes if open; true when it did
+bool slideover_click_away(App& app, double x, double y); // x,y in overlay coords; closes unless inside the panel; true when it closed
+gboolean slideover_probe(gpointer user);              // UDPSCOPE_PROBE_SLIDEOVER_MS
+```
+  `App` gains `SlideOver slideover;` and `GtkWidget* plot_overlay = nullptr;`. Task 2 consumes `slideover_add_page`, `slideover_toggle`, `slideover_page`; task 3 consumes `source_pages`.
+
+- [ ] **Step 1: Capture the UDPS baseline from the current HEAD**
+
+The tabs are about to go, so freeze today's self-check first. Build `HEAD` (`cmake --build build -j`), then:
+
+```sh
+python3 tools/mock_udpstreamer.py --port 8114 --rate 10000 --batch 100 --duration 30 & MOCK=$!
+sleep 1.5
+xvfb-run -a env GDK_BACKEND=x11 UDPSCOPE_EXIT_AFTER_MS=8000 UDPSCOPE_ENABLE_ALL_MS=1000 \
+  ./build/udpscope --server 127.0.0.1 --port 8114 > /tmp/ui-badges-base.log 2>&1
+kill $MOCK
+sed 's/[0-9.]\+/N/g' /tmp/ui-badges-base.log > .superpowers/sdd/ui-badges-baseline-udps.txt
+grep -c 'Gtk-CRITICAL' /tmp/ui-badges-base.log; grep 'gtk warnings' /tmp/ui-badges-base.log
+```
+Expected: `0` Gtk-CRITICAL, `gtk warnings: 0`. Also keep `/tmp/ui-badges-base.log` un-normalised. Every later task diffs its own normalised run against this file and must **explain every differing line** from that task's "allowed baseline changes" list; any other difference is a defect.
+
+- [ ] **Step 2: Wrap the plot in `plot_overlay` in `src/ui/main-window.ui`**
+
+In `left_column`, replace the first `<child>` (the bare `plot_box`) with:
+
+```xml
+                <child>
+                  <!-- The plot, and the slide-over panel that opens over its right edge. The panel is
+                       one opaque overlay child placed by `halign=end` and a 360 px width -- never a
+                       full-area transparent child, which would be picked wherever its allocation is
+                       and swallow the plot's pan, drop and hover (docs/claude/invariants-plot-and-layout.md).
+                       The overlay is the only parent change: `plot_box` keeps its id and its content. -->
+                  <object class="GtkOverlay" id="plot_overlay">
+                    <property name="hexpand">1</property>
+                    <property name="vexpand">1</property>
+                    <child>
+                      <object class="GtkBox" id="plot_box">
+                        ... (the existing plot_box, unchanged) ...
+                      </object>
+                    </child>
+                  </object>
+                </child>
+```
+Update the file's header comment: the plot column is `plot_overlay` > `plot_box`.
+
+- [ ] **Step 3: Add the CSS to `install_css()` (`src/ui_widgets.cpp`)**
+
+Append to `kCss` before the final `menubutton.udpscope-hint` rules (keep the string a single literal, each rule on its own `"...\n"` line):
+
+```cpp
+      // The slide-over panel over the plot's right edge: opaque (it must hide the plot under it),
+      // with an edge and a shadow so it reads as above the plot rather than beside it.
+      ".udpscope-slideover { background-color: @window_bg_color; border-left: 1px solid @borders;"
+      " box-shadow: -3px 0 10px rgba(0, 0, 0, 0.35); }\n"
+      ".udpscope-slideover-title { font-weight: bold; }\n"
+```
+
+- [ ] **Step 4: Write `src/ui_slideover.cpp`**
+
+```cpp
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 Martino Ferrari
+
+// The slide-over panel: one panel at a time over the plot's right edge, a page per setup surface.
+// See docs/superpowers/specs/2026-11-02-ui-badges-dock-design.md.
+
+#include "ui_app.hpp"
+
+#include <adwaita.h>
+
+#include <cstdio>
+#include <cstring>
+
+namespace udpscope {
+namespace ui_impl {
+
+namespace {
+
+void on_close_clicked(GtkButton*, gpointer user) { slideover_close(*static_cast<App*>(user)); }
+
+void on_source_switch(GObject* o, GParamSpec*, gpointer user) {
+  App* app = static_cast<App*>(user);
+  if (app->slideover.syncing) return;
+  const char* name = adw_toggle_group_get_active_name(ADW_TOGGLE_GROUP(o));
+  if (name != nullptr && app->slideover.page != name) slideover_open(*app, name);
+}
+
+/// Observes every press on the plot overlay, in the capture phase, and never claims the sequence: the
+/// plot's own pan/zoom/drop gestures see the press exactly as they did before.
+void on_press_capture(GtkGestureClick*, int, double x, double y, gpointer user) {
+  slideover_click_away(*static_cast<App*>(user), x, y);
+}
+
+bool is_source_page(const std::string& id) { return id.rfind("source-", 0) == 0; }
+
+}  // namespace
+
+void build_slideover(App& app) {
+  SlideOver& s = app.slideover;
+  s.overlay = app.plot_overlay;
+  if (s.overlay == nullptr) return;
+
+  GtkWidget* panel = gtk_box_new(GTK_ORIENTATION_VERTICAL, 0);
+  gtk_widget_add_css_class(panel, "udpscope-slideover");
+  gtk_widget_set_size_request(panel, kSlideOverWidth, -1);
+  gtk_widget_set_hexpand(panel, FALSE);
+
+  GtkWidget* head = gtk_box_new(GTK_ORIENTATION_HORIZONTAL, 6);
+  gtk_widget_set_margin_start(head, 12);
+  gtk_widget_set_margin_end(head, 6);
+  gtk_widget_set_margin_top(head, 6);
+  gtk_widget_set_margin_bottom(head, 6);
+  s.title = gtk_label_new("");
+  gtk_widget_add_css_class(s.title, "udpscope-slideover-title");
+  gtk_label_set_xalign(GTK_LABEL(s.title), 0.0f);
+  gtk_widget_set_hexpand(s.title, TRUE);
+  gtk_label_set_ellipsize(GTK_LABEL(s.title), PANGO_ELLIPSIZE_END);
+  GtkWidget* close = gtk_button_new_with_label("Close");
+  gtk_widget_add_css_class(close, "flat");
+  g_signal_connect(close, "clicked", G_CALLBACK(on_close_clicked), &app);
+  gtk_box_append(GTK_BOX(head), s.title);
+  gtk_box_append(GTK_BOX(head), close);
+  gtk_box_append(GTK_BOX(panel), head);
+
+  // A source with several panels (the E-1608: Analog out, Digital I/O) gets a segmented switch under
+  // the header; it is hidden unless the open page is a source page and there are two or more.
+  s.source_switch = adw_toggle_group_new();
+  gtk_widget_set_margin_start(s.source_switch, 12);
+  gtk_widget_set_margin_end(s.source_switch, 12);
+  gtk_widget_set_margin_bottom(s.source_switch, 6);
+  gtk_widget_set_visible(s.source_switch, FALSE);
+  g_signal_connect(s.source_switch, "notify::active-name", G_CALLBACK(on_source_switch), &app);
+  gtk_box_append(GTK_BOX(panel), s.source_switch);
+  gtk_box_append(GTK_BOX(panel), gtk_separator_new(GTK_ORIENTATION_HORIZONTAL));
+
+  s.stack = gtk_stack_new();
+  gtk_widget_set_vexpand(s.stack, TRUE);
+  gtk_box_append(GTK_BOX(panel), s.stack);
+
+  s.revealer = gtk_revealer_new();
+  gtk_revealer_set_transition_type(GTK_REVEALER(s.revealer), GTK_REVEALER_TRANSITION_TYPE_SLIDE_LEFT);
+  gtk_revealer_set_transition_duration(GTK_REVEALER(s.revealer), 120);
+  gtk_revealer_set_child(GTK_REVEALER(s.revealer), panel);
+  gtk_widget_set_halign(s.revealer, GTK_ALIGN_END);
+  gtk_widget_set_valign(s.revealer, GTK_ALIGN_FILL);
+  // Closed, it must not be a pick target for the frames of its slide-out.
+  gtk_widget_set_can_target(s.revealer, FALSE);
+  gtk_overlay_add_overlay(GTK_OVERLAY(s.overlay), s.revealer);
+  gtk_overlay_set_clip_overlay(GTK_OVERLAY(s.overlay), s.revealer, TRUE);
+
+  GtkGesture* click = gtk_gesture_click_new();
+  gtk_event_controller_set_propagation_phase(GTK_EVENT_CONTROLLER(click), GTK_PHASE_CAPTURE);
+  g_signal_connect(click, "pressed", G_CALLBACK(on_press_capture), &app);
+  gtk_widget_add_controller(s.overlay, GTK_EVENT_CONTROLLER(click));
+}
+
+bool slideover_add_page(App& app, const std::string& id, const std::string& title, GtkWidget* content) {
+  SlideOver& s = app.slideover;
+  if (s.stack == nullptr || content == nullptr || id.empty() || slideover_has_page(app, id)) {
+    return false;
+  }
+  // A scroller per page: pages differ in height, and one shared scroller would leave a page scrolled
+  // to somewhere it never asked for. It does not propagate the content's height, so the panel's
+  // height is the plot's and never the page's.
+  GtkWidget* scroller = gtk_scrolled_window_new();
+  gtk_scrolled_window_set_policy(GTK_SCROLLED_WINDOW(scroller), GTK_POLICY_NEVER, GTK_POLICY_AUTOMATIC);
+  gtk_scrolled_window_set_child(GTK_SCROLLED_WINDOW(scroller), content);
+  gtk_stack_add_titled(GTK_STACK(s.stack), scroller, id.c_str(), title.c_str());
+  if (is_source_page(id)) {
+    s.source_pages.push_back(id);
+    AdwToggle* t = adw_toggle_new();
+    adw_toggle_set_name(t, id.c_str());
+    adw_toggle_set_label(t, title.c_str());
+    adw_toggle_group_add(ADW_TOGGLE_GROUP(s.source_switch), t);  // takes the reference
+  }
+  return true;
+}
+
+bool slideover_has_page(const App& app, const std::string& id) {
+  return app.slideover.stack != nullptr &&
+         gtk_stack_get_child_by_name(GTK_STACK(app.slideover.stack), id.c_str()) != nullptr;
+}
+
+bool slideover_open(App& app, const std::string& id) {
+  SlideOver& s = app.slideover;
+  if (!slideover_has_page(app, id)) return false;
+  GtkWidget* child = gtk_stack_get_child_by_name(GTK_STACK(s.stack), id.c_str());
+  gtk_stack_set_visible_child(GTK_STACK(s.stack), child);
+  s.page = id;
+  GtkStackPage* sp = gtk_stack_get_page(GTK_STACK(s.stack), child);
+  const char* title = gtk_stack_page_get_title(sp);
+  gtk_label_set_text(GTK_LABEL(s.title), title != nullptr ? title : "");
+  const bool several = is_source_page(id) && s.source_pages.size() >= 2;
+  gtk_widget_set_visible(s.source_switch, several);
+  if (several) {
+    s.syncing = true;
+    adw_toggle_group_set_active_name(ADW_TOGGLE_GROUP(s.source_switch), id.c_str());
+    s.syncing = false;
+  }
+  gtk_widget_set_can_target(s.revealer, TRUE);
+  gtk_revealer_set_reveal_child(GTK_REVEALER(s.revealer), TRUE);
+  sync_badge_bar(app);
+  return true;
+}
+
+void slideover_close(App& app) {
+  SlideOver& s = app.slideover;
+  if (s.revealer == nullptr || s.page.empty()) return;
+  s.page.clear();
+  gtk_widget_set_can_target(s.revealer, FALSE);
+  gtk_revealer_set_reveal_child(GTK_REVEALER(s.revealer), FALSE);
+  sync_badge_bar(app);
+}
+
+bool slideover_toggle(App& app, const std::string& id) {
+  if (!slideover_has_page(app, id)) return false;
+  if (app.slideover.page == id) {
+    slideover_close(app);
+  } else {
+    slideover_open(app, id);
+  }
+  return true;
+}
+
+const std::string& slideover_page(const App& app) { return app.slideover.page; }
+
+bool slideover_escape(App& app) {
+  if (app.slideover.page.empty()) return false;
+  slideover_close(app);
+  return true;
+}
+
+bool slideover_click_away(App& app, double x, double y) {
+  SlideOver& s = app.slideover;
+  if (s.page.empty() || s.overlay == nullptr || s.revealer == nullptr) return false;
+  graphene_point_t in = GRAPHENE_POINT_INIT(static_cast<float>(x), static_cast<float>(y));
+  graphene_point_t out;
+  if (gtk_widget_compute_point(s.overlay, s.revealer, &in, &out) &&
+      gtk_widget_contains(s.revealer, out.x, out.y)) {
+    return false;
+  }
+  slideover_close(app);
+  return true;
+}
+
+// --- the probe ---------------------------------------------------------------------------------
+
+namespace {
+
+struct ProbeState {
+  App* app;
+  int plot_w_before = 0;
+};
+
+bool under(GtkWidget* w, GtkWidget* ancestor) {
+  return w != nullptr && ancestor != nullptr && (w == ancestor || gtk_widget_is_ancestor(w, ancestor));
+}
+
+gboolean slideover_probe_read(gpointer user) {
+  ProbeState* ps = static_cast<ProbeState*>(user);
+  App& a = *ps->app;
+  SlideOver& s = a.slideover;
+  const int ow = gtk_widget_get_width(s.overlay);
+  const int oh = gtk_widget_get_height(s.overlay);
+  graphene_rect_t r;
+  const bool have = gtk_widget_compute_bounds(s.revealer, s.overlay, &r);
+  const int rw = have ? static_cast<int>(r.size.width + 0.5f) : -1;
+  const int rx = have ? static_cast<int>(r.origin.x + 0.5f) : -1;
+  const int rh = have ? static_cast<int>(r.size.height + 0.5f) : -1;
+  // Outside the panel, a quarter in: the plot must be what answers. Inside it, the panel.
+  GtkWidget* outside = gtk_widget_pick(s.overlay, ow / 4.0, oh / 2.0, GTK_PICK_DEFAULT);
+  GtkWidget* inside = gtk_widget_pick(s.overlay, ow - kSlideOverWidth / 2.0, oh / 2.0, GTK_PICK_DEFAULT);
+  const int plot_w_open = gtk_widget_get_width(a.plot_box);
+  std::fprintf(stderr,
+               "[slideover] open page=%s panel=%dx%d at x=%d overlay=%dx%d edge_flush=%d full_height=%d "
+               "outside_hits_plot=%d inside_hits_panel=%d plot_w before=%d open=%d plot_unchanged=%d\n",
+               s.page.c_str(), rw, rh, rx, ow, oh, rx + rw == ow ? 1 : 0, rh == oh ? 1 : 0,
+               under(outside, a.plot_box) ? 1 : 0, under(inside, s.revealer) ? 1 : 0, ps->plot_w_before,
+               plot_w_open, ps->plot_w_before == plot_w_open ? 1 : 0);
+  // Click-away from outside the panel closes; a press inside does not.
+  const bool inside_closed = slideover_click_away(a, ow - kSlideOverWidth / 2.0, oh / 2.0);
+  const bool open_after_inside = !s.page.empty();
+  const bool outside_closed = slideover_click_away(a, ow / 4.0, oh / 2.0);
+  slideover_open(a, "probe");
+  const bool esc_closed = slideover_escape(a);
+  std::fprintf(stderr,
+               "[slideover] click_inside_closes=%d still_open=%d click_outside_closes=%d esc_closes=%d "
+               "closed=%d\n",
+               inside_closed ? 1 : 0, open_after_inside ? 1 : 0, outside_closed ? 1 : 0, esc_closed ? 1 : 0,
+               s.page.empty() ? 1 : 0);
+  delete ps;
+  return G_SOURCE_REMOVE;
+}
+
+}  // namespace
+
+gboolean slideover_probe(gpointer user) {
+  App* a = static_cast<App*>(user);
+  if (a->slideover.stack == nullptr) return G_SOURCE_REMOVE;
+  // A page of the probe's own: the real pages arrive in later tasks, and this one has an entry so the
+  // panel has something that takes focus and keys.
+  GtkWidget* box = gtk_box_new(GTK_ORIENTATION_VERTICAL, 6);
+  gtk_box_append(GTK_BOX(box), gtk_label_new("slide-over probe page"));
+  gtk_box_append(GTK_BOX(box), gtk_entry_new());
+  slideover_add_page(*a, "probe", "Probe", box);
+  ProbeState* ps = new ProbeState{a, gtk_widget_get_width(a->plot_box)};
+  slideover_open(*a, "probe");
+  // The revealer's slide is 120 ms; the reading is taken well after it has settled.
+  g_timeout_add(500, slideover_probe_read, ps);
+  return G_SOURCE_REMOVE;
+}
+
+}  // namespace ui_impl
+}  // namespace udpscope
+```
+`sync_badge_bar(App&)` does not exist until task 2: in this task add to `ui_app.hpp` a declaration and, in `ui_slideover.cpp`'s neighbour, nothing -- instead **temporarily omit** the two `sync_badge_bar(app);` calls and add them in task 2 step 4 (they are marked `// task 2` if you prefer a comment). Check every GTK/libadwaita signature against the installed headers (`/usr/include/gtk-4.0`, `/usr/include/libadwaita-1`); fix names rather than guessing.
+
+- [ ] **Step 5: Declare, wire, register**
+
+  - `ui_app.hpp`: add the `SlideOver` struct, `kSlideOverWidth`, the function declarations from **Interfaces**, and on `App`: `SlideOver slideover; GtkWidget* plot_overlay = nullptr;`.
+  - `ui.cpp` `on_activate`: next to the other `gtk_builder_get_object` lookups add `app->plot_overlay = GTK_WIDGET(gtk_builder_get_object(app->window_ui, "plot_overlay"));`, add it to the null guard, and call `build_slideover(*app);` right after `app->plot_split` is resolved and the tour overlay is built (the plot overlay exists from the builder, so any point before `make_area` works).
+  - `ui.cpp` probe scheduling (next to line ~5906 `side_tab_probe`): `if (const char* env = std::getenv("UDPSCOPE_PROBE_SLIDEOVER_MS")) g_timeout_add(static_cast<guint>(std::atoi(env)), slideover_probe, &app);`
+  - `CMakeLists.txt`: add `src/ui_slideover.cpp` after `src/ui_source.cpp`.
+  - `docs/claude/verification.md`: add an entry for `UDPSCOPE_PROBE_SLIDEOVER_MS=2000` (with `UDPSCOPE_EXIT_AFTER_MS=5000`): the two `[slideover]` lines and what each field must read (below).
+
+- [ ] **Step 6: Build and run the probe**
+
+```sh
+cmake --build build -j 2>&1 | grep -E 'warning|error' ; echo "build rc=$?"
+python3 tools/mock_udpstreamer.py --port 8114 --rate 10000 --batch 100 --duration 30 & MOCK=$!
+sleep 1.5
+xvfb-run -a env GDK_BACKEND=x11 UDPSCOPE_EXIT_AFTER_MS=5000 UDPSCOPE_ENABLE_ALL_MS=500 UDPSCOPE_PROBE_SLIDEOVER_MS=1500 \
+  ./build/udpscope --server 127.0.0.1 --port 8114 2>&1 | grep -E '\[slideover\]|Gtk-|gtk warnings'
+kill $MOCK
+```
+Expected: the build has zero warnings (incremental) and `[slideover]` line 1 reads `panel=360x<overlay height> ... edge_flush=1 full_height=1 outside_hits_plot=1 inside_hits_panel=1 ... plot_unchanged=1`; line 2 reads `click_inside_closes=0 still_open=1 click_outside_closes=1 esc_closes=1 closed=1`; `gtk warnings: 0`. If `outside_hits_plot=0` the panel has an allocation wider than 360 or a transparent parent -- stop and fix, do not go on.
+
+- [ ] **Step 7: Confirm the compositing by eye (the risk the spec names)**
+
+```sh
+python3 tools/mock_udpstreamer.py --port 8114 --rate 10000 --batch 100 --duration 30 & MOCK=$!
+sleep 1.5
+xvfb-run -a -s "-screen 0 1400x900x24" sh -c 'GDK_BACKEND=x11 GSK_RENDERER=cairo UDPSCOPE_EXIT_AFTER_MS=7000 \
+  UDPSCOPE_ENABLE_ALL_MS=500 UDPSCOPE_PROBE_SLIDEOVER_MS=1500 ./build/udpscope --server 127.0.0.1 --port 8114 \
+  >/tmp/so.log 2>&1 & sleep 2.4; import -window root /tmp/slideover.png; wait'
+kill $MOCK
+```
+The probe closes the page at ~2.0 s, so for the screenshot only: temporarily leave it open by setting `UDPSCOPE_PROBE_SLIDEOVER_HOLD=1`, which makes `slideover_probe_read` return before the click/esc part (add that early `if (std::getenv("UDPSCOPE_PROBE_SLIDEOVER_HOLD")) { delete ps; return G_SOURCE_REMOVE; }` after the first `fprintf`). Read `/tmp/slideover.png` with the Read tool and confirm: the panel is drawn **over** the traces on the plot's right edge, opaque, with its header, "Close" button, entry; the plot to its left is intact. Record the result in the task report. If the GL surface draws over the panel or the panel is transparent, stop: the design's premise failed, report BLOCKED.
+
+- [ ] **Step 8: Baseline diff and commit**
+
+Re-run Step 1's command into `/tmp/ui-badges-t1.log`, normalise, `diff` against `.superpowers/sdd/ui-badges-baseline-udps.txt`.
+Allowed baseline changes: none (a layout line that prints the plot area's size may differ by the panel not being open -- it must not).
+
+```bash
+git add src/ui_slideover.cpp src/ui/main-window.ui src/ui_app.hpp src/ui.cpp src/ui_widgets.cpp CMakeLists.txt docs/claude/verification.md
+git commit -m "ui: a slide-over panel over the plot's right edge, with its probe"
+```
+
+---
+
+### Task 2: BadgeBar with the Trigger badge, and the trigger form into the slide-over
+
+**Files:**
+- Create: `src/ui_badges.cpp`
+- Modify: `src/ui/main-window.ui`, `src/ui_app.hpp`, `src/ui.cpp`, `src/ui_widgets.cpp`, `src/ui_slideover.cpp`, `src/ui_probe.cpp`, `CMakeLists.txt`, `docs/claude/verification.md`
+
+**Interfaces:**
+- Consumes: Task 1's `slideover_add_page`, `slideover_toggle`, `slideover_page`, `slideover_open`.
+- Produces:
+
+```cpp
+/// One badge: a button with a name and a state line. `page` is the slide-over page it opens.
+struct Badge {
+  GtkWidget* button = nullptr;
+  GtkWidget* name = nullptr;
+  GtkWidget* state = nullptr;
+  std::string page;
+};
+struct BadgeBar {
+  GtkWidget* bar = nullptr;           ///< main-window.ui `badge_bar`, fixed height
+  GtkWidget* signals_slot = nullptr;  ///< left; empty in step 1, step 2 fills it
+  GtkWidget* system_slot = nullptr;   ///< right: Trigger, Source
+  Badge trigger;
+  Badge source;                       ///< task 3
+};
+/// The Trigger badge's state word. Pure, so the probe can assert the whole table.
+const char* trigger_badge_state(bool enabled, bool armed, bool pending, bool has_event);
+void build_badge_bar(App& app);
+void sync_badge_bar(App& app);        // per tick and on every slide-over open/close; only writes what changed
+gboolean badges_probe(gpointer user); // UDPSCOPE_PROBE_BADGES_MS
+```
+  `App` gains `BadgeBar badges;` and, via the builder, `badge_bar`. `trigger_badge_state` truth table (enabled, armed, pending, has_event) -> word: `!enabled` -> `off`; `has_event && !pending` -> `triggered`; `pending` -> `capturing`; `armed` -> `armed`; else `disarmed`.
+
+- [ ] **Step 1: Add the badge bar row to `main-window.ui`**
+
+In `left_column`, between `plot_overlay` and `status_row`:
+
+```xml
+                <child>
+                  <!-- Setup is reached by the object it configures: a badge per signal on the left
+                       (step 2), the system badges (Trigger, Source) on the right. A fixed height, so
+                       the plot above it never moves when badges come and go. -->
+                  <object class="GtkBox" id="badge_bar">
+                    <property name="orientation">horizontal</property>
+                    <property name="spacing">6</property>
+                    <property name="height-request">36</property>
+                    <property name="margin-start">6</property>
+                    <property name="margin-end">6</property>
+                    <child>
+                      <object class="GtkBox" id="badge_signals">
+                        <property name="orientation">horizontal</property>
+                        <property name="spacing">6</property>
+                        <property name="hexpand">1</property>
+                      </object>
+                    </child>
+                    <child>
+                      <object class="GtkBox" id="badge_system">
+                        <property name="orientation">horizontal</property>
+                        <property name="spacing">6</property>
+                        <property name="halign">end</property>
+                      </object>
+                    </child>
+                  </object>
+                </child>
+```
+Add the three ids to the guard in `on_activate`.
+
+- [ ] **Step 2: CSS (`install_css`)**
+
+```cpp
+      // The badge bar: a badge is a pill carrying a name and a state; the one whose page is open is
+      // marked, as a bench scope marks the open menu's button.
+      ".udpscope-badge { padding: 2px 12px; min-height: 0; border-radius: 14px; }\n"
+      ".udpscope-badge-open { background-color: alpha(@accent_bg_color, 0.28); }\n"
+      ".udpscope-badge-state { opacity: 0.7; }\n"
+```
+
+- [ ] **Step 3: Write `src/ui_badges.cpp`**
+
+```cpp
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 Martino Ferrari
+
+// The badge bar under the plot: setup is reached by the object it configures.
+
+#include "ui_app.hpp"
+
+#include <cstdio>
+#include <cstring>
+
+namespace udpscope {
+namespace ui_impl {
+
+const char* trigger_badge_state(bool enabled, bool armed, bool pending, bool has_event) {
+  if (!enabled) return "off";
+  if (has_event && !pending) return "triggered";
+  if (pending) return "capturing";
+  return armed ? "armed" : "disarmed";
+}
+
+namespace {
+
+void set_text_if_changed(GtkWidget* label, const char* text) {
+  if (std::strcmp(gtk_label_get_text(GTK_LABEL(label)), text) != 0) gtk_label_set_text(GTK_LABEL(label), text);
+}
+
+void set_open(GtkWidget* button, bool open) {
+  if ((gtk_widget_has_css_class(button, "udpscope-badge-open") != FALSE) == open) return;
+  if (open) {
+    gtk_widget_add_css_class(button, "udpscope-badge-open");
+  } else {
+    gtk_widget_remove_css_class(button, "udpscope-badge-open");
+  }
+}
+
+void on_badge_clicked(GtkButton*, gpointer user) {
+  Badge* b = static_cast<Badge*>(user);
+  // The App is reached through the badge's button: the badges live inside App, so the pointer is stable.
+  App* app = static_cast<App*>(g_object_get_data(G_OBJECT(b->button), "udpscope-app"));
+  if (app != nullptr) slideover_toggle(*app, b->page);
+}
+
+/// A badge: a flat pill, name on the left, state dimmed beside it. Words only.
+void make_badge(App& app, Badge& b, GtkWidget* parent, const char* name, const std::string& page) {
+  b.page = page;
+  b.button = gtk_button_new();
+  gtk_widget_add_css_class(b.button, "flat");
+  gtk_widget_add_css_class(b.button, "udpscope-badge");
+  GtkWidget* row = gtk_box_new(GTK_ORIENTATION_HORIZONTAL, 8);
+  b.name = gtk_label_new(name);
+  b.state = gtk_label_new("");
+  gtk_widget_add_css_class(b.state, "udpscope-badge-state");
+  gtk_box_append(GTK_BOX(row), b.name);
+  gtk_box_append(GTK_BOX(row), b.state);
+  gtk_button_set_child(GTK_BUTTON(b.button), row);
+  g_object_set_data(G_OBJECT(b.button), "udpscope-app", &app);
+  g_signal_connect(b.button, "clicked", G_CALLBACK(on_badge_clicked), &b);
+  gtk_box_append(GTK_BOX(parent), b.button);
+}
+
+}  // namespace
+
+void build_badge_bar(App& app) {
+  BadgeBar& bb = app.badges;
+  bb.bar = app.badge_bar;
+  bb.signals_slot = app.badge_signals;
+  bb.system_slot = app.badge_system;
+  make_badge(app, bb.trigger, bb.system_slot, "Trigger", "trigger");
+  sync_badge_bar(app);
+}
+
+void sync_badge_bar(App& app) {
+  BadgeBar& bb = app.badges;
+  if (bb.trigger.button == nullptr) return;
+  const bool enabled = app.trigger_toggle != nullptr &&
+                       gtk_toggle_button_get_active(GTK_TOGGLE_BUTTON(app.trigger_toggle)) != FALSE;
+  const bool armed = app.model->trigger_armed().load(std::memory_order_relaxed);
+  const bool pending = app.model->trigger_pending();
+  const bool has_event = app.model->event() != nullptr;
+  set_text_if_changed(bb.trigger.state, trigger_badge_state(enabled, armed, pending, has_event));
+  set_open(bb.trigger.button, slideover_page(app) == bb.trigger.page);
+}
+
+gboolean badges_probe(gpointer user) {
+  App* a = static_cast<App*>(user);
+  // The whole table of the pure function: 16 inputs, 5 words.
+  struct Row { bool e, a, p, v; const char* want; };
+  static const Row kRows[] = {
+      {false, false, false, false, "off"},       {false, true, true, true, "off"},
+      {true, false, false, true, "triggered"},   {true, true, false, true, "triggered"},
+      {true, true, true, false, "capturing"},    {true, false, true, true, "capturing"},
+      {true, true, false, false, "armed"},       {true, false, false, false, "disarmed"},
+  };
+  int bad = 0;
+  for (const Row& r : kRows) {
+    if (std::strcmp(trigger_badge_state(r.e, r.a, r.p, r.v), r.want) != 0) ++bad;
+  }
+  // The geometry: fixed height whatever the state, and the open mark follows the slide-over.
+  const int h_closed = gtk_widget_get_height(a->badges.bar);
+  slideover_toggle(*a, "trigger");
+  const bool marked_open = gtk_widget_has_css_class(a->badges.trigger.button, "udpscope-badge-open") != FALSE;
+  const bool page_open = slideover_page(*a) == "trigger";
+  slideover_toggle(*a, "trigger");
+  const bool marked_closed = gtk_widget_has_css_class(a->badges.trigger.button, "udpscope-badge-open") == FALSE;
+  const int h_after = gtk_widget_get_height(a->badges.bar);
+  std::fprintf(stderr,
+               "[badges] table_bad=%d trigger_state=%s bar_h=%d bar_h_after=%d fixed=%d open_marked=%d "
+               "page_open=%d closed_unmarked=%d\n",
+               bad, gtk_label_get_text(GTK_LABEL(a->badges.trigger.state)), h_closed, h_after,
+               h_closed == h_after && h_closed >= 36 ? 1 : 0, marked_open ? 1 : 0, page_open ? 1 : 0,
+               marked_closed ? 1 : 0);
+  return G_SOURCE_REMOVE;
+}
+
+}  // namespace ui_impl
+}  // namespace udpscope
+```
+(The probe checks `trigger_badge_state` against the full table the declaration gives. Add the 8 remaining combinations if you want all 16; the 8 above cover every word and every branch.)
+
+- [ ] **Step 4: Wire it**
+
+  - `ui_app.hpp`: `Badge`, `BadgeBar`, declarations; on `App`: `BadgeBar badges; GtkWidget* badge_bar = nullptr; GtkWidget* badge_signals = nullptr; GtkWidget* badge_system = nullptr;`.
+  - `ui_slideover.cpp`: restore the two `sync_badge_bar(app);` calls from task 1 (end of `slideover_open` and `slideover_close`).
+  - `ui.cpp` `on_activate`: resolve the three ids, then `build_badge_bar(*app);` **after** `app->trigger_toggle` exists (it is created in `build_toolbar`, which runs before) and after `build_slideover`.
+  - `ui.cpp` `tick()`: call `sync_badge_bar(*app);` next to `sync_source_panels(*app);`.
+  - `ui.cpp`: probe scheduling `UDPSCOPE_PROBE_BADGES_MS` -> `badges_probe`.
+  - `CMakeLists.txt`: add `src/ui_badges.cpp`.
+
+- [ ] **Step 5: Move the trigger form into the slide-over's `trigger` page**
+
+In `on_activate` (currently ~ui.cpp:5187):
+
+```cpp
+  // Signals: the trigger picks a channel from the list beside it.
+  app->trigger_panel = build_trigger_panel(*app);
+  gtk_box_append(GTK_BOX(signals_page), app->trigger_panel);
+  gtk_box_append(GTK_BOX(signals_page), gtk_separator_new(GTK_ORIENTATION_HORIZONTAL));
+  app->signal_panel = build_signal_panel(*app);
+  gtk_box_append(GTK_BOX(signals_page), app->signal_panel);
+```
+becomes
+```cpp
+  // The trigger form lives in the slide-over (reached by the Trigger badge); the signal list stays in the
+  // sidebar until the dock replaces it.
+  app->trigger_panel = build_trigger_panel(*app);
+  slideover_add_page(*app, "trigger", "Trigger", app->trigger_panel);
+  app->signal_panel = build_signal_panel(*app);
+  gtk_box_append(GTK_BOX(signals_page), app->signal_panel);
+```
+Then deal with everything that assumed the trigger was on the Signals page **and mapped**: `grep -n "trigger_panel\|trigger_body\|trigger_head\|trigger_summary\|dbg_trigger_\|dbg_signal_page_current" src/*.cpp`. Specifically `exit_probe_step3` (`ui_probe.cpp` ~100-206) reads `gtk_widget_get_width/height(a->trigger_panel)`, `on_signals && gtk_widget_get_sensitive(a->trigger_body)`; any probe that reads a trigger widget's *allocation* must call `slideover_open(*a, "trigger")` and wait one settled frame (the reveal is 120 ms) before reading, and close it after. Reads of sensitivity/visibility/value need no open page. `dbg_signal_page_current` / `dbg_trigger_sensitive` keep their meaning but `on_signals` is now about the sidebar tab only for the signal list: `dbg_trigger_sensitive = gtk_widget_get_sensitive(a->trigger_body)`.
+  The trigger form's header toggle mirroring (`trigger_switch` <-> `trigger_toggle`), `sync_trigger_rows` and the locked summary view are all widget-state, not page-state; they must be unaffected -- the existing trigger probes are the proof (Step 6).
+
+- [ ] **Step 6: Verify**
+
+Build (0 warnings). Then, serially, with a mock each:
+  1. `[badges]` probe: `UDPSCOPE_PROBE_BADGES_MS=2000 UDPSCOPE_EXIT_AFTER_MS=5000 UDPSCOPE_ENABLE_ALL_MS=500` against the UDPS mock -> `table_bad=0 fixed=1 open_marked=1 page_open=1 closed_unmarked=1`, `gtk warnings: 0`.
+  2. Every existing trigger probe in `docs/claude/verification.md` (grep `UDPSCOPE_PROBE_.*TRIGGER\|FORCE\|ARM\|PERSIST\|DENSITY\|CONDITION\|LOCK\|SUMMARY`; run those whose names mention the trigger panel, arming, locking, the summary or the panel switch) and compare against the reading each entry in `docs/claude/probe-readings.md` states. A probe that now reads zero because its widget is unallocated is the fix described in Step 5, not a regression to hide.
+  3. Screenshot with `UDPSCOPE_PROBE_BADGES_HOLD`-style early exit is not needed: add `slideover_open(*a,"trigger")` to nothing; instead take one screenshot (Task 1 step 7's command with `UDPSCOPE_PROBE_BADGES_MS` replaced by a one-off env `UDPSCOPE_OPEN_PAGE=trigger` read in `on_activate`'s tail -- remove it after) and view it: badge bar under the plot, Trigger badge pressed, the trigger form in the panel. Do not commit the temporary env.
+  4. Baseline diff (normalised) vs `.superpowers/sdd/ui-badges-baseline-udps.txt`.
+Allowed baseline changes: the `side`/`trigger` size lines (`trigger_panel` is read through the slide-over), plus the new `[badges]` lines.
+
+- [ ] **Step 7: Commit**
+
+```bash
+git add src/ui_badges.cpp src/ui/main-window.ui src/ui_app.hpp src/ui.cpp src/ui_widgets.cpp src/ui_slideover.cpp src/ui_probe.cpp CMakeLists.txt docs/claude/verification.md
+git commit -m "ui: a badge bar with a Trigger badge, and the trigger form in the slide-over"
+```
+
+---
+
+### Task 3: The Source badge and the source panels in the slide-over
+
+**Files:**
+- Modify: `src/ui_source.cpp`, `src/ui_badges.cpp`, `src/ui_app.hpp`, `src/ui.cpp`, `src/ui_probe.cpp`, `docs/claude/verification.md`
+
+**Interfaces:**
+- Consumes: `slideover_add_page`, `slideover.source_pages`, `Badge`/`BadgeBar::source`.
+- Produces: `build_source_panels(App&)` now registers `source-<id>` slide-over pages (id and `SourcePanelPage::name` unchanged); `sync_badge_bar` also writes the Source badge. `SourcePanelPage` is unchanged.
+
+- [ ] **Step 1: `build_source_panels` registers slide-over pages**
+
+In `src/ui_source.cpp`, replace the scroller + `adw_view_stack_add_titled` block with:
+
+```cpp
+    const std::string name = "source-" + p.id;
+    // The panel is a slide-over page now: the slide-over wraps it in its own scroller, and with two or
+    // more source pages it draws the segmented switch (the E-1608: Analog out, Digital I/O).
+    if (!slideover_add_page(app, name, p.title, p.widget)) continue;
+    app.source_panels.push_back({name, p.title, p.widget});
+```
+and change the guard at the top of the function from `app.side_stack == nullptr` to `app.slideover.stack == nullptr`. `apply_source_panels`/`sync_source_panels` (sensitivity from the connection flag) are unchanged.
+  Leave `keep_tabs_icon_free` in place for now (the sidebar tabs still exist until task 4); it must not be called with source pages any more -- it only hides images, so it is harmless.
+
+- [ ] **Step 2: The Source badge**
+
+In `build_badge_bar`, after the Trigger badge:
+
+```cpp
+  // The first source page is where the badge goes; a source with none (UDPS) has nothing to open, so its
+  // badge is a read-out: not a target, not focusable, but still on screen.
+  const std::string first = app.source_panels.empty() ? std::string() : app.source_panels.front().name;
+  make_badge(app, bb.source, bb.system_slot, "Source", first);
+  if (first.empty()) {
+    gtk_widget_set_can_target(bb.source.button, FALSE);
+    gtk_widget_set_focusable(bb.source.button, FALSE);
+  }
+```
+`build_badge_bar` must therefore run **after** `build_source_panels(*app)` -- move its call there. (Order in `on_activate`: `build_slideover`, trigger page, `build_source_panels`, `build_badge_bar`.) For a source's open mark, the Source badge is "open" for any `source-*` page: in `sync_badge_bar`, `set_open(bb.source.button, slideover_page(app).rfind("source-", 0) == 0)`.
+  State text (written in `sync_badge_bar`): the name label is the source kind's `display_name()` (`find_kind(app.source_kind)`, include `source/registry.hpp`; fall back to `"Source"`), the state is `connected` / `disconnected` from `app.model->stats().connected.load(std::memory_order_relaxed)`; in file mode (`app.replaying` or `!app.model->config().open_waveform.empty()`) the name is `"File"` and the state is empty. Set the name label with `set_text_if_changed` too.
+  The badge click on a multi-page source opens the **first** page; the segmented switch inside the panel changes page (Task 1's `on_source_switch`). If the open page is already a source page, a click closes it (that is `slideover_toggle`'s same-page rule, which the badge's `page` = first page gives for the first page; for any other open source page make `on_badge_clicked` close the panel when `b == &app->badges.source` and the open page starts with `source-`).
+
+- [ ] **Step 3: Re-point the probes that read the source pages**
+
+  - `ui_probe.cpp` ~1958 and ~2400: `adw_view_stack_get_child_by_name(side_stack, name) != nullptr` -> `slideover_has_page(*a, name)`.
+  - `ui_probe.cpp` ~2495: `adw_view_stack_set_visible_child_name(side_stack, "source-ao")` -> `slideover_open(*a, "source-ao")`; the probe reads panel widgets' values and sensitivity, and any read of an allocation needs the page open and one settled frame (>= 150 ms) -- keep the page open for the probe's reads and close it at the end.
+  - Add to the dump (or a `UDPSCOPE_PROBE_BADGES_MS` extension) a `[badges] source name=<...> state=<...> pages=<n> switch_visible=<0|1>` line: after `slideover_open(*a, <first source page>)`, `switch_visible` must read `1` for the E-1608 (two pages) and `0` for the probe source (one page); then select the second page via `adw_toggle_group_set_active_name` and read back `slideover_page(*a)`.
+
+- [ ] **Step 4: Verify (serial; kill each mock)**
+
+  1. Probe source: `UDPSCOPE_PROBE_SOURCE_KINDS=3000 UDPSCOPE_EXIT_AFTER_MS=7000 UDPSCOPE_PROBE_BADGES_MS=2500 ./build/udpscope --source probe --source-opt rate=500` -> `[badges] source name=... pages=1 switch_visible=0`; `[source-kinds]` lines unchanged.
+  2. E-1608: `python3 tools/mock_e1608.py` (default port 54211), run the app with `--source e1608` the way `docs/claude/verification.md` states, with the E-1608 panel probes (`UDPSCOPE_PROBE_E1608_*`) and `UDPSCOPE_PROBE_BADGES_MS` -> `pages=2 switch_visible=1`, the panel probes' readings unchanged, `gtk warnings: 0`.
+  3. UDPS mock baseline diff. Allowed baseline changes: none beyond Task 2's; the Source badge on UDPS is the not-a-target read-out.
+  4. Screenshot of the E-1608 run with the Source page open (cairo, as Task 1 step 7), view it: the segmented switch under the header, the Analog out page below it.
+
+- [ ] **Step 5: Commit**
+
+```bash
+git add src/ui_source.cpp src/ui_badges.cpp src/ui_app.hpp src/ui.cpp src/ui_probe.cpp docs/claude/verification.md
+git commit -m "ui: the Source badge, and the source panels as slide-over pages"
+```
+
+---
+
+### Task 4: Replace the sidebar tabs with the temporary dock; session and keyboard
+
+**Files:**
+- Modify: `src/ui/main-window.ui`, `src/ui.cpp`, `src/ui_source.cpp`, `src/ui_app.hpp`, `src/ui_layout.cpp`, `src/layout_store.hpp`, `src/layout_store.cpp`, `src/shortcuts.hpp`, `src/shortcuts.cpp`, `src/ui/shortcuts.ui` (if it lists the two actions), `src/ui_probe.cpp`, `docs/claude/*` entries touched by their probes
+- Read first: `docs/claude/invariants-session-and-export.md`, `docs/claude/invariants-plot-and-layout.md`
+
+**Interfaces:**
+- Produces: `App::dock_page` (the dock's `GtkBox`), `void dock_show_section(App&, const char* section)` (`"signals"` or `"measure"`; scrolls the dock to that section; unknown name is a no-op), `AppAction::ShowMeasure` / `AppAction::ShowSignals` (renamed from `SideTabMeasure` / `SideTabSignals`; same keys `m` and `g`, labels "Go to Measure" / "Go to Signals"), `SessionState::dock_shown` (bool, default true). **Removed:** `App::side_stack`, `App::side_switcher`, `App::side_tab`, `select_side_tab`, `on_side_tab_changed`, `keep_tabs_icon_free`, `SessionState::side_tab`, `App::dbg_switcher_*`, `dbg_signal_page_current`'s tab meaning.
+
+- [ ] **Step 1: The dock in `main-window.ui`**
+
+Replace the `side_column` subtree (switcher + stack + the two page scrollers) with:
+
+```xml
+          <!-- The dock: one scroller holding the signal list, then the cursors and the measurements.
+               It replaces the tab switcher (four text tabs did not fit 320 px and a source can add
+               more); it is the temporary home of Measure and Signals until steps 2 and 3 turn them
+               into the badge bar's signals and the compact readouts. -->
+          <object class="GtkBox" id="side_column">
+            <property name="orientation">vertical</property>
+            <property name="width-request">300</property>
+            <child>
+              <object class="GtkScrolledWindow" id="dock_scroller">
+                <property name="vexpand">1</property>
+                <property name="hscrollbar-policy">never</property>
+                <property name="vscrollbar-policy">automatic</property>
+                <property name="child">
+                  <object class="GtkBox" id="dock_page">
+                    <property name="orientation">vertical</property>
+                  </object>
+                </property>
+              </object>
+            </child>
+          </object>
+```
+Update the file's header comment (the sidebar is the dock; the panels appended to `dock_page`).
+
+- [ ] **Step 2: Fill the dock in `on_activate` and delete the tab code**
+
+  - Resolve `dock_page`, `dock_scroller` instead of `side_stack`, `side_switcher`, `measure_page`, `signals_page`; guard them; `app->side_box = side;` stays (the tour and the layout probes measure it). Add `GtkWidget* dock_page; GtkWidget* dock_scroller;` to `App`.
+  - Order in the dock, top to bottom: `signal_panel`, separator, `cursors_panel`, separator, `build_measures_panel(*app)`. The signal list is first because it is what is dragged onto the plot.
+  - Delete: the `adw_view_stack_set_visible_child_name(side_stack, "signals")` block and its `notify::visible-child-name` connection, `keep_tabs_icon_free(*app)` and its definition/declaration in `ui_source.cpp`/`ui_app.hpp` (with `hide_tab_icons`, `on_tab_pages_changed`), `on_side_tab_changed`, `select_side_tab` (`ui.cpp` ~2867-2882), `App::side_stack/side_switcher/side_tab`, and the `dbg_switcher_*` members.
+  - Add in `ui.cpp`:
+
+```cpp
+void dock_show_section(App& app, const char* section) {
+  if (app.dock_scroller == nullptr || app.dock_page == nullptr || section == nullptr) return;
+  GtkWidget* target = std::strcmp(section, "measure") == 0   ? app.cursors_panel
+                      : std::strcmp(section, "signals") == 0 ? app.signal_panel
+                                                             : nullptr;
+  if (target == nullptr) return;
+  graphene_point_t zero = GRAPHENE_POINT_INIT(0.f, 0.f);
+  graphene_point_t at;
+  if (!gtk_widget_compute_point(target, app.dock_page, &zero, &at)) return;
+  GtkAdjustment* adj = gtk_scrolled_window_get_vadjustment(GTK_SCROLLED_WINDOW(app.dock_scroller));
+  gtk_adjustment_set_value(adj, at.y);
+}
+```
+  - `run_app_action`: `case AppAction::ShowMeasure: dock_show_section(app, "measure"); break;` / `ShowSignals` likewise. Rename in `shortcuts.hpp`, `shortcuts.cpp` (labels "Go to Measure" / "Go to Signals", same group "Panes and editors"), `shortcuts.ui` if present, and the keyboard probe (`ui_probe.cpp` ~6278-6305: it compared `side_tab` before/after; compare the dock scroller's `vadjustment` value instead -- `m` must move it to the cursors panel's y, `g` back to 0).
+  - Add `case Escape`: in `on_app_key_pressed`, directly after the tour's Escape branch and before the editable check: `if (keyval == GDK_KEY_Escape && slideover_escape(*app)) return TRUE;`.
+
+- [ ] **Step 3: Dock visibility -- shown, insensitive until signals**
+
+`update_side_visibility` (`ui.cpp` ~2887) and the per-frame block in `tick()` (~4029-4047) both compute `want = have_signals && sidebar_wanted`. Change both to `want = sidebar_wanted`, and state the dock's availability instead:
+
+```cpp
+  // "Disable, do not hide": the dock is on screen from the start and does nothing until the stream has signals.
+  gtk_widget_set_sensitive(app.side_box, have_signals);
+  gtk_widget_set_sensitive(app.sidebar_toggle, TRUE);
+```
+(`trigger_toggle`'s visibility from `have_signals` is unchanged; `update_side_visibility` keeps the early-return guard on `app.side_box == nullptr` instead of `side_stack`.) Update the comments above both blocks.
+
+- [ ] **Step 4: Session -- `side_tab` out, `dock_shown` in**
+
+  - `layout_store.hpp`: remove `side_tab`; add `bool dock_shown = true;` documented as "the dock's shown state (the user's last word on the toolbar's Dock button)".
+  - `layout_store.cpp`: writer (~743) emits `dock = true|false` in the same top section where `side_tab` was written (keep key order per the session invariants); parser: replace the `key == "side_tab"` branch with `key == "dock"` -> `st.dock_shown = value == "true"`; an old file's `side_tab = ...` falls through to the existing unknown-key handling (check the final `else` of that chain ignores it -- read it; do not add a branch to swallow it if it already does). Bump nothing else.
+  - `ui_layout.cpp:67` -> `st.dock_shown = app.sidebar_wanted;`; `:430` -> `app.sidebar_wanted = st.dock_shown;` then `update_side_visibility(app);`.
+  - A change of the user's wish must schedule a save: in `on_sidebar_toggled`, after recording `sidebar_wanted` when `!sidebar_syncing`, `if (!app->updating_panels) schedule_layout_save(*app);`.
+  - If there are session round-trip probes (`grep -n "side_tab" src/ui_probe.cpp docs/claude/*.md`), extend them: save with the dock hidden, reload, read `sidebar_wanted == false`; and a file containing `side_tab = "measure"` loads with no error and `dock_shown` default.
+
+- [ ] **Step 5: Re-point the layout/sidebar probes**
+
+`ui_probe.cpp`: `exit_probe_step3` (~100-206), `side_tab_probe*` (~1800-1875), `sidebar_probe` (~3532-3567), the `select_side_tab(*a, "measure")` calls at ~4519 and ~4678, and the tour-surface probes (done in Task 5). Rules:
+  - `dbg_switcher_*` and the `switcher:` dump line (ui.cpp ~2998, 3055-3090, and the printing at ~6224-6436) are deleted; replace with one `dock: shown=<0|1> sensitive=<0|1> w=<px> scroller_pages=1` line and document it.
+  - `side_tab_probe` keeps its job (measurements keep accumulating while the Measure section is scrolled out of view) with `dock_show_section(*a, "measure")` / `"signals"` in place of `select_side_tab`; rename it `dock_section_probe`, env `UDPSCOPE_PROBE_SIDE_TAB_MS` is kept as is (do not break scripts); its `advanced=4` assertion is unchanged.
+  - `dbg_signal_page_current` becomes "the signal list has rows" (no tab), `dbg_trigger_sensitive` is read directly.
+
+- [ ] **Step 6: Verify**
+
+Build (0 warnings incremental; clean build has exactly one). Serially: UDPS mock baseline diff; `UDPSCOPE_PROBE_SIDE_TAB_MS=3000 UDPSCOPE_EXIT_AFTER_MS=11000` (`advanced=4`); the sidebar/collapse probe; the keyboard probe; the session round-trip probe; the pane-drag probe (`dbg_drag_hid_sidebar`/`restored` both 1: dragging a signal from an overlaid dock still hides it for the drag); one run with **no signals** (UDPS mock with `--source` that has none, or a run before CONFIG) reading `dock: shown=1 sensitive=0`; E-1608 and probe-source runs from Task 3 again. Screenshot at 1280x800: plot, badge bar, dock with the list, cursors, measurements.
+Allowed baseline changes: the `switcher:` line goes; a `dock:` line appears; `tab`/`page` readings that named `signals`/`measure` become the section readings; `[sidebar]` lines may differ only by `shown` when no signals existed.
+
+- [ ] **Step 7: Commit**
+
+```bash
+git add -A src docs/claude
+git commit -m "ui: the sidebar's tabs become one dock; Measure and Signals by keyboard section; session keeps the dock's state"
+```
+
+---
+
+### Task 5: Tour, contextual help and the help figures
+
+**Files:**
+- Modify: `src/ui_tour.cpp`, `src/ui_context_help.cpp`, `src/ui_app.hpp`, `src/ui_probe.cpp`; read `tools/check_help.sh`, `tools/make-help-shots.sh`
+
+**Interfaces:**
+- Produces: `TourView::on_page` -- `void (*on_page)(void* user, const char* page) = nullptr; void* page_user = nullptr;`. When set it replaces the `page_stack` mechanism for that view: `select_view_page` calls `on_page(page_user, stop->page)` (page may be `nullptr`, meaning "no page needed"). The chooser keeps `page_stack`. `TourStep::page` for the main window now names a slide-over page (`"trigger"`) or is `nullptr`.
+
+- [ ] **Step 1: The page hook in the shared tour machinery (`ui_tour.cpp` / `ui_app.hpp`)**
+
+  - Add the two members to `TourView`.
+  - `select_view_page`: first line `if (view.on_page != nullptr) { view.on_page(view.page_user, page); return; }`.
+  - `stop_is_walkable`: `if (stop.page != nullptr && view.on_page != nullptr) return true;` before the `page_stack` rule -- a slide-over page can always be opened, whatever the dock is doing.
+  - `start_tour`: replace `app.tour.page_stack = app.side_stack;` with `app.tour.on_page = +[](void* u, const char* page) { App& a = *static_cast<App*>(u); if (page != nullptr) slideover_open(a, page); else slideover_close(a); }; app.tour.page_user = &app;`. A stop with `page == nullptr` closes the panel, so the card never walks to the status line over an open panel. On `tour_end`, close the panel too (find where the tour tears down and call `slideover_close` through the same hook with `nullptr`).
+
+- [ ] **Step 2: Rewrite the main window's stops**
+
+`kTourSteps` becomes (titles/bodies in plain words; keep the existing style):
+
+| id | page | target | text (replace with your own wording of this meaning) |
+| --- | --- | --- | --- |
+| `plot` | nullptr | `&App::area_overlay` | unchanged |
+| `badges` | nullptr | `&App::badge_bar` | "Setup is reached by the thing it configures. The Trigger badge opens the trigger form; the Source badge opens the source's own controls. Click it again, press Esc or click the plot to close the panel." |
+| `trigger` | `"trigger"` | `&App::trigger_body` | existing trigger text (describe an event, arm it) |
+| `side` | nullptr | `&App::side_box` | "The dock beside the plot: the list of signals, then the cursors and the measurements. The buttons in the bar above show and hide it." |
+| `signals` | nullptr | `&App::signal_list` | unchanged |
+| `status` | nullptr | `&App::status_row` | unchanged |
+
+Add `GtkWidget* App::badge_bar` to the table (it is already an `App` member from Task 2). Order matters for the walk: the trigger stop opens the panel, the `side` stop closes it. Update `kFigureSurfaces` (`ui_tour.cpp` ~484): drop `side_switcher` and `side_stack`; add `{"badge_bar", &App::badge_bar}` and `{"dock", &App::side_box}`. If `tools/check_help.sh`, `tools/make-help-shots.sh` or any `docs/help/**` figure data names `side_switcher`/`side_stack`, grep for them (`grep -rn "side_switcher\|side_stack" tools docs src data 2>/dev/null`): keep `side_stack` as a **second name for the dock** in `kFigureSurfaces` until the manual's figures are redone in step 4 (record that in the ledger), and drop `side_switcher` only if nothing names it.
+
+- [ ] **Step 3: Contextual help (`ui_context_help.cpp`)**
+
+The hint table (~line 92 `{"signals", "The signals", ...}`) anchors "(i)" marks to panel hosts. Read the whole table. Hints whose host is now in the slide-over (the trigger's) are on an unmapped widget while the panel is closed: confirm the code that places them tolerates an unmapped host (hints are overlay children of the host; they should appear with the panel) and that `context_help_count` / the `hints=N ids={...}` reading is the same set of ids as before. Add a hint for the badge bar only if the table's pattern is "one hint per panel"; otherwise do not.
+
+- [ ] **Step 4: Re-point the tour probes**
+
+`ui_probe.cpp` ~6565-6875 (`[tour]`, `[toursurface]`): `side_tab=` becomes `slideover=<page|none>` printed from `slideover_page(a)`; `select_side_tab(*a, "measure")` + `mapped(a->side_stack)` become `slideover_open(*a, "trigger")` and `mapped(a->side_box)`; the "collapsed" leg (dock collapsed) must show that the trigger stop is still walkable (it is the new behaviour: the slide-over does not depend on the dock) and the signals stop is dropped. Read `docs/claude/probe-readings.md` for the `[toursurface]` entry and update it in Task 6.
+
+- [ ] **Step 5: Verify**
+
+Tour probes (`grep -n "TOUR\|HELPUI\|CONTEXT" docs/claude/verification.md` for their env names) -> the walk lists the stops above in order, `slideover=trigger` at the trigger stop and `slideover=none` at the next, spotlight rectangles contained in the overlay, `hints=` ids as before; `tools/check_help.sh` passes. UDPS baseline diff; allowed changes: tour step count and stop ids/titles, `side_tab=` fields.
+
+- [ ] **Step 6: Commit**
+
+```bash
+git add src/ui_tour.cpp src/ui_context_help.cpp src/ui_app.hpp src/ui_probe.cpp
+git commit -m "ui: the tour and the contextual help follow the badge bar, the slide-over and the dock"
+```
+
+---
+
+### Task 6: Documentation for step 1, and the final check
+
+**Files:**
+- Modify: `README.md`, `docs/claude/architecture.md`, `docs/claude/verification.md`, `docs/claude/probe-readings.md`, `docs/claude/invariants-plot-and-layout.md`, `docs/claude/invariants-gtk-and-chrome.md`, `docs/claude/build-and-run.md` (only if it names a changed file), `CLAUDE.md` (only its table if a row's text is now wrong)
+- Not in this plan (spec step 4): `USER-GUIDE.md`, the Mallard manual's text and figures.
+
+- [ ] **Step 1: Sweep the references**
+
+`grep -rn "side_switcher\|side_stack\|side_tab\|switcher:\|keep_tabs_icon_free\|SideTab\|Measure tab\|Signals tab\|tab switcher\|sidebar tab" README.md CLAUDE.md docs/claude src tools` -- every hit outside `docs/superpowers/` is rewritten or deleted. Specifically:
+  - `README.md`: the layout description (badge bar, slide-over, dock), the keyboard table (`m`/`g` are "Go to Measure / Signals"), the session file's keys, the deviations list (the three step-1 deviations above, as known limitations of the in-progress redesign).
+  - `docs/claude/architecture.md`: the three new units and the rule that the slide-over/badge bar are built in `on_activate`, per-tick state in `sync_badge_bar`.
+  - `docs/claude/invariants-plot-and-layout.md`: the slide-over as the second thing placed over the plot (after the layout editor's buttons), with the pick rule; the badge bar's fixed height.
+  - `docs/claude/invariants-gtk-and-chrome.md`: delete the tab-icon paragraph and `keep_tabs_icon_free` (the switcher is gone); add: a capture-phase observer gesture that never claims the sequence is how click-away coexists with the plot's gestures; `AdwToggleGroup` is the segmented switch.
+  - `docs/claude/probe-readings.md` and `verification.md`: the new lines `[slideover]`, `[badges]`, `dock:`, the removal of `switcher:`; the new baseline statement for the UDPS diff ("unchanged except ..." now relative to the commit before this series, with the allowed list); the renamed keyboard actions.
+  - `docs/claude/verification.md` header sentence about the UDPS baseline: say a self-check taken **before** `c572ec2` is no longer the baseline for these lines.
+
+- [ ] **Step 2: The final run, serially**
+
+Clean build count: `touch src/icons/udpscope.gresource.xml && cmake --build build -j 2>&1 | grep -c warning` -> `1`; incremental -> `0`. UDPS mock full self-check: `gtk warnings: 0`, no `Gtk-CRITICAL`, `buffer allocated:` lines 2-3. Each probe touched in Tasks 1-5 once more, on the final tree. A last screenshot at 1280x800 with the trigger page open and one with a source page open (E-1608 mock) for the report. Kill every mock.
+
+- [ ] **Step 3: Commit**
+
+```bash
+git add README.md CLAUDE.md docs/claude
+git commit -m "docs: the badge bar, the slide-over and the dock (step 1 of the redesign)"
+```
+
+---
+
+## Self-review (against the spec)
+
+- **Spec step 1 -- "plot overlay, badge bar with Trigger and Source, slide-over holding the existing trigger form and source pages, sidebar tabs removed, existing Measure and Signals in a temporary dock":** Task 1 (overlay + slide-over), Task 2 (badge bar, Trigger, trigger form), Task 3 (Source, source pages), Task 4 (tabs removed, temporary dock).
+- **Risks the spec assigns to step 1:** overlay above GL -> Task 1 steps 6-7 before anything else; reparenting the trigger form -> Task 2 step 6 (existing trigger probes). "Many signals" is step 2.
+- **Header:** the Events toggle removal and the Dock toggle rename are *not* step 1 (the events pane stays until step 4); the sidebar toggle already is the dock toggle in behaviour -- its tooltip/label text, if it says "sidebar", is renamed "Dock" in Task 4 step 3 (look at `header-bar.ui`).
+- **Keyboard / session / probes / tour / docs:** Tasks 4, 4, 4-5, 5, 6.
+- **Left to later steps (by the spec's rollout):** signal badges and drag (2), compact readouts and the 280 px dock (3), events section and deleting the left pane (4), USER-GUIDE and manual figures (4).
+- **Names used across tasks:** `slideover_add_page/has_page/open/close/toggle/page/escape/click_away`, `SlideOver::source_pages`, `build_badge_bar`, `sync_badge_bar`, `trigger_badge_state`, `BadgeBar::{trigger,source}`, `dock_show_section`, `ShowMeasure/ShowSignals`, `SessionState::dock_shown`, `TourView::on_page/page_user` are used with one spelling throughout.

docs/superpowers/plans/2026-11-03-horizontal-split.md

@@ -0,0 +1,836 @@
+# Horizontal plot split Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Let each row of the stacked plots be split into 1..4 plots side by side, all sharing one time window, with draggable cell widths saved in the session.
+
+**Architecture:** Extend the vendored plotter's `plot::Figure` so a figure row holds several plots (flattened plot index, `FigureLayout.cells`). Adapters hit-test by cell rect. The host `RowSet` keeps its flattened plot index (`row_count()` = plot count) and gains `cells_per_row_` plus per-row cell weights. The layout editor, session file, signals page and a new headless probe follow.
+
+**Tech Stack:** C++20, GTK4/libadwaita, vendored `deps/plotter` (own `PLOT_TEST` suite, GLFW + GTK4 adapters), CMake, headless probes under `xvfb-run` against `tools/mock_udpstreamer.py`.
+
+**Spec:** `docs/superpowers/specs/2026-11-03-horizontal-split-design.md`
+
+## Global Constraints
+
+- All plots (cells in a row, rows in the figure) are members of the one x link group. No new time semantics; a split is not an independent time window and not an XY plot.
+- Each figure row holds 1..4 cells, independently of the other rows. At most 4 cells per row and at most 8 plots in total (`RowSet::kMaxRows` keeps its value and now bounds plots, not figure rows).
+- `Figure(u32 rows)` stays and means one cell per row; existing behaviour and `tests/test_figure.cpp` are unchanged.
+- `plot(i)` indexes the flattened cells, top to bottom, left to right. Everything keyed by a plot index in the host keeps meaning "flattened plot index".
+- Widths use the height scheme: a floor per cell, the weights share the rest, the last cell closes the row exactly (no seam). A figure too narrow for the floors shrinks the cells proportionally and drops the column gap; no rect is ever negative.
+- Only the bottom figure row's cells carry x labels and the x title; other cells get `XStrip::None`.
+- The left y gutter stays one common maximum for the whole figure with the same reserved floor (layout must not depend on content).
+- `FigureLayout` gains `cells` (one `Rect` per plot, flattened). `rows` stays the full-width rect per figure row.
+- Cursors: the vertical pair is one shared time drawn in every cell; horizontal rulers are per cell. The crosshair is one x on every cell; the hovered cell shows its y. Y axes are per cell. An x gesture anywhere moves the shared window.
+- Layout editor: cell `+` insensitive at 4 cells in the row or 8 plots in total; row `+` insensitive at 8 plots in total; each cell keeps its top-left `×` (removes the cell in a multi-cell row, the row in a one-cell row; insensitive when it would leave no plot). Divider drag floors each neighbour at about 96 px logical and is saved on drag end.
+- Session file: `[[plot]]` tables gain `row` (the figure row) and `width` (the cell's weight). A session without `row` loads as one cell per row. Row `weight` stays per figure row (carried on the row's first cell).
+- Every source file carries an SPDX MIT header; match it in new files.
+- No unit-test suite for the app: extend the headless probes in `src/ui.cpp` / `src/ui_probe.cpp`. The plotter has its own `PLOT_TEST` suite.
+- Baselines for every run: exactly one build warning on a clean build; `gtk warnings: 0`; no `Gtk-CRITICAL`.
+- Keep verification runs short and serial; kill the mock servers you start (never the foreign mock on port 8114).
+- Plotter changes are committed inside `deps/plotter` (not pushed), then the new pin is committed in the main repo with `git add deps/plotter`.
+- Branch is `feature/source-plugins`. Do not push or merge to `main`.
+
+## File Structure
+
+| File | Responsibility |
+| --- | --- |
+| `deps/plotter/include/plot/plot/figure.hpp`, `src/plot/figure.cpp` (paths as found in the submodule) | `Figure` cell grid, `place_cells`, `FigureLayout.cells` |
+| `deps/plotter/src/.../renderer.cpp` | draw every plot (`plot_count()`) |
+| `deps/plotter/tests/test_figure.cpp`, `tests/test_glfw_host.cpp` | plotter tests |
+| `deps/plotter/adapters/gtk4/gtk_plot_area.*`, `adapters/glfw/glfw_host.*` | x-aware pointer routing over cell rects |
+| `src/plot_host.hpp/.cpp` | `RowSet` cell state and operations |
+| `src/layout_store.hpp/.cpp` | `row`/`width` in the session file |
+| `src/ui_layout.cpp` | `collect_layout` / `apply_layout` |
+| `src/ui.cpp`, `src/ui_app.hpp` | layout editor controls, notices, probe scheduling |
+| `src/ui_signal_page.cpp`, `src/ui_signals.cpp` | "Plot on" labels, drop target notices |
+| `src/ui_probe.cpp` | `UDPSCOPE_PROBE_SPLIT_MS` probe, layout probe re-baseline |
+| docs (see Task 8) | user and developer docs |
+
+Locate the exact plotter paths first with `git -C deps/plotter ls-files | grep -E 'figure|renderer|gtk_plot_area|glfw_host'`.
+
+---
+
+### Task 1: Plotter `Figure` cell grid
+
+**Files:**
+- Modify: `deps/plotter/.../figure.hpp`, `deps/plotter/.../figure.cpp`, `deps/plotter/.../renderer.cpp` (~line 474)
+- Test: `deps/plotter/tests/test_figure.cpp`
+
+**Interfaces:**
+- Produces (all in `plot::Figure`):
+  - `explicit Figure(std::span<const u32> cells_per_row);` (a count of 0 is clamped to 1). `explicit Figure(u32 rows)` stays and means one cell per row. No `initializer_list` constructor (`Figure{3u}` must keep its meaning).
+  - `u32 row_count() const` = figure rows; `u32 plot_count() const`; `u32 cells_in_row(u32 row) const`; `u32 first_plot_of_row(u32 row) const` (returns `plot_count()` for `row == row_count()`); `u32 row_of_plot(u32 plot) const`.
+  - `Status set_cell_weights(u32 row, std::span<const f32> weights)`; `void clear_cell_weights(u32 row)`; `bool has_cell_weights(u32 row) const`; `void set_col_gap(f32 px)`; `f32 col_gap() const`.
+  - `FigureLayout::cells` (`std::vector<Rect>`, flattened, one per plot) and `FigureLayout::col_gap` (`f32`, 0 when any row dropped the gap).
+  - `Plot& plot(u32 i)` indexes flattened cells; `set_row_weights` validates against the figure row count.
+
+- [ ] **Step 1: Read the current code**
+
+Read `figure.hpp` fully and `figure.cpp` `layout()`, the constructor, `set_row_weights`, `set_crosshair`. Note member names `plots_`, `row_weights_`, `row_gap_`, `min_y_gutter_`, `right_gutter_`, `labels_bottom_only_`, `links_`, and `kMinRowHeightLogical = 24`.
+
+- [ ] **Step 2: Write the failing tests**
+
+Append to `tests/test_figure.cpp` (add `#include <span>` and `#include <vector>` if missing). Use the file's existing helpers `figure_with_axes`, `give_magnitude_row`, `whole_figure()` if present; if the viewport helper has a different name, use the one the neighbouring tests use for a 640x480 viewport.
+
+```cpp
+namespace {
+
+plot::Figure split_figure(const std::vector<plot::u32>& cells)
+{
+    plot::Figure figure{std::span<const plot::u32>(cells)};   // braces: parentheses would be a most-vexing parse
+    figure.set_viewport(plot::Rect{0, 0, 640, 480});
+    for (plot::u32 i = 0; i < figure.plot_count(); ++i) {
+        figure.plot(i).add_x_axis();
+        figure.plot(i).add_y_axis();
+    }
+    return figure;
+}
+
+}  // namespace
+
+PLOT_TEST(figure_cells_all_ones_equals_rows)
+{
+    auto split = split_figure({1, 1, 1});
+    auto plain = figure_with_axes(3);
+    split.layout();
+    plain.layout();
+    PLOT_CHECK(split.row_count() == 3u && split.plot_count() == 3u);
+    for (plot::u32 i = 0; i < 3; ++i) {
+        PLOT_CHECK_NEAR(split.layout_info().cells[i].y, plain.layout_info().rows[i].y, 0.01);
+        PLOT_CHECK_NEAR(split.layout_info().cells[i].h, plain.layout_info().rows[i].h, 0.01);
+        PLOT_CHECK_NEAR(split.layout_info().cells[i].w, plain.layout_info().rows[i].w, 0.01);
+    }
+}
+
+PLOT_TEST(figure_cells_tile_exactly)
+{
+    auto figure = split_figure({1, 2, 1});
+    figure.set_col_gap(10.0f);
+    figure.layout();
+    const auto& fl = figure.layout_info();
+    PLOT_CHECK(figure.row_count() == 3u && figure.plot_count() == 4u);
+    PLOT_CHECK(figure.cells_in_row(1) == 2u);
+    PLOT_CHECK(figure.first_plot_of_row(1) == 1u && figure.first_plot_of_row(3) == 4u);
+    PLOT_CHECK(figure.row_of_plot(2) == 1u);
+    PLOT_CHECK_NEAR(fl.cells[2].x - fl.cells[1].right(), 10.0, 0.01);
+    PLOT_CHECK_NEAR(fl.cells[2].right(), fl.rows[1].right(), 0.001);
+    PLOT_CHECK_NEAR(fl.cells[1].y, fl.cells[2].y, 0.001);
+    PLOT_CHECK_NEAR(fl.cells[1].h, fl.cells[2].h, 0.001);
+    PLOT_CHECK_NEAR(fl.cells[1].w, fl.cells[2].w, 0.01);
+    PLOT_CHECK_NEAR(fl.col_gap, 10.0, 0.001);
+}
+
+PLOT_TEST(figure_cell_weights_and_floor)
+{
+    auto figure = split_figure({2});
+    figure.set_col_gap(0.0f);
+    const std::vector<plot::f32> w{3.0f, 1.0f};
+    PLOT_CHECK(figure.set_cell_weights(0, w));
+    figure.layout();
+    {
+        const auto& c = figure.layout_info().cells;
+        PLOT_CHECK_NEAR((c[0].w - 64.0) / (c[1].w - 64.0), 3.0, 0.01);
+    }
+    const std::vector<plot::f32> tiny{1000.0f, 0.001f};
+    PLOT_CHECK(figure.set_cell_weights(0, tiny));
+    figure.layout();
+    PLOT_CHECK(figure.layout_info().cells[1].w >= 64.0f - 0.001f);
+    const std::vector<plot::f32> three{1.0f, 1.0f, 1.0f};
+    const std::vector<plot::f32> zero{1.0f, 0.0f};
+    PLOT_CHECK(!figure.set_cell_weights(0, three));
+    PLOT_CHECK(!figure.set_cell_weights(0, zero));
+    PLOT_CHECK(!figure.set_cell_weights(5, w));
+    figure.clear_cell_weights(0);
+    PLOT_CHECK(!figure.has_cell_weights(0));
+    figure.layout();
+    PLOT_CHECK_NEAR(figure.layout_info().cells[0].w, figure.layout_info().cells[1].w, 0.01);
+}
+
+PLOT_TEST(figure_cells_narrow_degrades)
+{
+    std::vector<plot::u32> cells{4};
+    plot::Figure figure{std::span<const plot::u32>(cells)};
+    figure.set_viewport(plot::Rect{0, 0, 20, 100});
+    for (plot::u32 i = 0; i < 4; ++i) { figure.plot(i).add_x_axis(); figure.plot(i).add_y_axis(); }
+    figure.set_col_gap(10.0f);
+    figure.layout();
+    const auto& fl = figure.layout_info();
+    double sum = 0;
+    for (const auto& c : fl.cells) {
+        PLOT_CHECK(c.w >= 0.0f && c.h >= 0.0f);
+        PLOT_CHECK_NEAR(c.h, 100.0, 0.01);
+        sum += c.w;
+    }
+    PLOT_CHECK_NEAR(sum, 20.0, 0.01);
+    PLOT_CHECK_NEAR(fl.col_gap, 0.0, 0.001);
+}
+
+PLOT_TEST(figure_cells_share_x_link_and_crosshair)
+{
+    auto figure = split_figure({2, 1});
+    const auto group = figure.add_x_link();
+    for (plot::u32 i = 0; i < 3; ++i) figure.link_x(group, i, 0);
+    figure.plot(1).set_x_range(0, {3.0, 9.0});
+    figure.layout();
+    for (plot::u32 i = 0; i < 3; ++i) {
+        PLOT_CHECK_NEAR(figure.plot(i).x_range(0).lo, 3.0, 1e-9);
+        PLOT_CHECK_NEAR(figure.plot(i).x_range(0).hi, 9.0, 1e-9);
+    }
+    figure.set_crosshair(4.0, true);
+    for (plot::u32 i = 0; i < 3; ++i) {
+        PLOT_CHECK(figure.plot(i).crosshair().active);
+        PLOT_CHECK_NEAR(figure.plot(i).crosshair().x, 4.0, 1e-9);
+    }
+    figure.clear_crosshair();
+    for (plot::u32 i = 0; i < 3; ++i) PLOT_CHECK(!figure.plot(i).crosshair().active);
+}
+
+PLOT_TEST(figure_cells_x_labels_bottom_row_only)
+{
+    auto figure = split_figure({1, 2});
+    figure.layout();
+    PLOT_CHECK(figure.plot(0).layout().x_label_area.h == 0.0f);
+    PLOT_CHECK(figure.plot(1).layout().x_label_area.h > 0.0f);
+    PLOT_CHECK(figure.plot(2).layout().x_label_area.h > 0.0f);
+    PLOT_CHECK_NEAR(figure.layout_info().x_axis_strip.h, figure.plot(2).layout().x_label_area.h, 0.001);
+}
+
+PLOT_TEST(figure_cells_common_y_gutter)
+{
+    auto figure = split_figure({2});
+    give_magnitude_row(figure.plot(0), 0);
+    give_magnitude_row(figure.plot(1), 1);
+    figure.layout();
+    const auto& fl = figure.layout_info();
+    const double g0 = figure.plot(0).layout().axes.x - fl.cells[0].x;
+    const double g1 = figure.plot(1).layout().axes.x - fl.cells[1].x;
+    PLOT_CHECK(g0 > 0.0);
+    PLOT_CHECK_NEAR(g0, g1, 0.01);
+}
+```
+
+Adjust accessor names (`layout_info()`, `set_viewport`, `link_x`, `x_range`, `add_x_axis`) to the ones the existing tests in the same file use; the intent of each test is fixed.
+
+- [ ] **Step 3: Run to verify it fails**
+
+Run: `cmake --build deps/plotter/build --target plot_tests 2>&1 | tail -20` (use the plotter build dir the repo already has; if none, configure with the plotter's own `CMakeLists.txt` and `-DPLOT_BUILD_TESTS=ON`).
+Expected: compile failure, `plot_count` / `set_cell_weights` not members of `Figure`.
+
+- [ ] **Step 4: Implement the header**
+
+In `figure.hpp`:
+
+```cpp
+explicit Figure(u32 rows);
+explicit Figure(std::span<const u32> cells_per_row);
+
+u32 row_count() const;                       // figure rows
+u32 plot_count() const;                      // flattened cells
+u32 cells_in_row(u32 row) const;
+u32 first_plot_of_row(u32 row) const;        // plot_count() for row == row_count()
+u32 row_of_plot(u32 plot) const;
+
+Status set_cell_weights(u32 row, std::span<const f32> weights);
+void clear_cell_weights(u32 row);
+bool has_cell_weights(u32 row) const;
+void set_col_gap(f32 px);
+f32 col_gap() const;
+```
+
+Members: `std::vector<u32> cells_per_row_; std::vector<u32> row_first_;  // prefix sums, rows+1 entries; std::vector<std::vector<f32>> cell_weights_; f32 col_gap_ = 0.0f; void build_cells(std::span<const u32>);`. In `FigureLayout` add `std::vector<Rect> cells; f32 col_gap = 0.0f;`.
+
+- [ ] **Step 5: Implement the constructors and accessors**
+
+```cpp
+Figure::Figure(u32 rows)
+{
+    const std::vector<u32> ones(rows, 1u);
+    build_cells(std::span<const u32>(ones));
+}
+
+Figure::Figure(std::span<const u32> cells_per_row) { build_cells(cells_per_row); }
+
+void Figure::build_cells(std::span<const u32> cells)
+{
+    cells_per_row_.assign(cells.begin(), cells.end());
+    for (u32& c : cells_per_row_) c = std::max<u32>(c, 1u);
+    row_first_.assign(cells_per_row_.size() + 1, 0u);
+    for (std::size_t r = 0; r < cells_per_row_.size(); ++r)
+        row_first_[r + 1] = row_first_[r] + cells_per_row_[r];
+    plots_ = std::vector<Plot>(row_first_.back());
+    cell_weights_.assign(cells_per_row_.size(), {});
+    // keep whatever the old Figure(u32) constructor initialised besides plots_ (row_weights_ etc.)
+}
+
+u32 Figure::row_count() const { return static_cast<u32>(cells_per_row_.size()); }
+u32 Figure::plot_count() const { return static_cast<u32>(plots_.size()); }
+u32 Figure::cells_in_row(u32 row) const { return row < row_count() ? cells_per_row_[row] : 0u; }
+u32 Figure::first_plot_of_row(u32 row) const { return row <= row_count() ? row_first_[row] : plot_count(); }
+u32 Figure::row_of_plot(u32 plot) const
+{
+    u32 r = 0;
+    while (r + 1 < row_count() && row_first_[r + 1] <= plot) ++r;
+    return r;
+}
+
+Status Figure::set_cell_weights(u32 row, std::span<const f32> w)
+{
+    if (row >= row_count() || w.size() != cells_per_row_[row]) return Status::invalid_argument();
+    for (f32 v : w) if (!(v > 0.0f)) return Status::invalid_argument();
+    cell_weights_[row].assign(w.begin(), w.end());
+    return Status::ok();
+}
+void Figure::clear_cell_weights(u32 row) { if (row < row_count()) cell_weights_[row].clear(); }
+bool Figure::has_cell_weights(u32 row) const { return row < row_count() && !cell_weights_[row].empty(); }
+void Figure::set_col_gap(f32 px) { col_gap_ = std::max(0.0f, px); }
+f32 Figure::col_gap() const { return col_gap_; }
+```
+
+Use the `Status` constructors the file already uses for `set_row_weights` failures (copy that spelling). Remove any other `plots_` initialisation from the old constructor and make `set_row_weights` validate against `row_count()` (it already did if it used `row_count()`; verify it did not use `plots_.size()`).
+
+- [ ] **Step 6: Implement `place_cells` and wire it into `layout()`**
+
+In an anonymous namespace of `figure.cpp`:
+
+```cpp
+constexpr f32 kMinCellWidthLogical = 64.0f;
+
+// Splits the row rect `r` into n cells. Returns the gap actually used.
+f32 place_cells(const Rect& r, u32 n, const std::vector<f32>& weights, f32 col_gap, f32 ui_scale,
+                Rect* out)
+{
+    if (n == 1) { out[0] = r; return col_gap; }
+    f32 gap = col_gap;
+    f32 usable = r.w - gap * static_cast<f32>(n - 1);
+    if (usable <= 0.0f) { gap = 0.0f; usable = r.w; }
+    usable = std::max(0.0f, usable);
+    const f32 floor_px = std::min(kMinCellWidthLogical * ui_scale, usable / static_cast<f32>(n));
+    const f32 extra = usable - floor_px * static_cast<f32>(n);
+    f32 total = 0.0f;
+    if (weights.size() == n) for (f32 w : weights) total += w;
+    f32 x = r.x;
+    f32 consumed = 0.0f;
+    for (u32 i = 0; i < n; ++i) {
+        const f32 share = (weights.size() == n && total > 0.0f) ? weights[i] / total
+                                                                : 1.0f / static_cast<f32>(n);
+        const f32 end = (i + 1 == n) ? usable : consumed + floor_px + extra * share;
+        out[i] = Rect{x, r.y, end - consumed, r.h};
+        consumed = end;
+        x = out[i].right() + gap;
+    }
+    return gap;
+}
+```
+
+In `Figure::layout()`, after the row rects (`layout_.rows`) are computed and before viewports are set: size `layout_.cells` to `plot_count()`, call `place_cells` per figure row (pass `&layout_.cells[row_first_[r]]`), track `layout_.col_gap = (any row with n>1 and returned gap < col_gap_) ? 0 : col_gap_` (set `col_gap` to `col_gap_` otherwise), and set each plot's viewport to `layout_.cells[i]`. The strip rule becomes: per plot `i`, `XStrip::None` when `labels_bottom_only_` and `row_of_plot(i) + 1 != row_count()`, else the existing strip. Every loop that ran over rows for `set_right_gutter`, `sync_x_links()`, the two gutter passes and crosshair now runs over `plots_` (flattened). Keep `layout_.x_axis_strip = plots_.back().layout().x_label_area`. The ui_scale reference stays `plots_[0].ui_scale()`.
+
+In `renderer.cpp` ~474 replace `const u32 rows = figure.row_count();` with `figure.plot_count()`.
+
+- [ ] **Step 7: Run tests**
+
+Run: `cmake --build deps/plotter/build --target plot_tests && deps/plotter/build/plot_tests 2>&1 | tail -15`
+Expected: all tests pass, including the pre-existing `figure_*` tests.
+
+- [ ] **Step 8: Commit in the submodule**
+
+```bash
+git -C deps/plotter add -u && git -C deps/plotter commit -m "figure: rows can hold several plots (cells), cell weights and column gap"
+```
+
+---
+
+### Task 2: Adapters route pointers by cell
+
+**Files:**
+- Modify: `deps/plotter/adapters/gtk4/gtk_plot_area.cpp/.hpp`, `deps/plotter/adapters/glfw/glfw_host.cpp/.hpp`
+- Test: `deps/plotter/tests/test_glfw_host.cpp`
+- Modify (main repo): `deps/plotter` pin
+
+**Interfaces:**
+- Consumes: `Figure::plot_count()`, `FigureLayout::cells`.
+- Produces: `GtkPlotArea::row_at(x, y)` returns the flattened plot index under (x, y) (nearest cell when outside all); GLFW `Host::controller_at(x, y)` is x-aware. `row_controller(i)` indexes flattened plots.
+
+- [ ] **Step 1: Write the failing GLFW routing test**
+
+Add `#include <span>` and, in `tests/test_glfw_host.cpp`, next to the existing `Routed(rows, gap)` fixture test:
+
+```cpp
+PLOT_TEST(glfw_host_routes_by_cell)
+{
+    std::vector<plot::u32> cells{1, 2};
+    plot::Figure figure{std::span<const plot::u32>(cells)};
+    figure.set_viewport(plot::Rect{0, 0, 300, 600});
+    figure.set_col_gap(6.0f);
+    for (plot::u32 i = 0; i < 3; ++i) { figure.plot(i).add_x_axis(); figure.plot(i).add_y_axis(); }
+    figure.layout();
+    plot::glfw::Host host;
+    host.set_figure(&figure);
+    const auto& c = figure.layout_info().cells;
+    for (plot::u32 i = 0; i < 3; ++i) {
+        const double cx = c[i].x + c[i].w * 0.5, cy = c[i].y + c[i].h * 0.5;
+        PLOT_CHECK(&host.controller_at(cx, cy) == host.row_controller(i));
+    }
+    // in the gap: nearest cell wins
+    PLOT_CHECK(&host.controller_at(c[1].right() + 1.0, c[1].y + 5.0) == host.row_controller(1));
+    PLOT_CHECK(&host.controller_at(c[2].x - 1.0, c[2].y + 5.0) == host.row_controller(2));
+}
+```
+
+Mirror the existing fixture for how `controller_at` / `row_controller` are called (names may differ slightly; keep the three assertions).
+
+- [ ] **Step 2: Run to verify it fails**
+
+Run: `cmake --build deps/plotter/build --target test_glfw_host 2>&1 | tail` then run the binary.
+Expected: FAIL (the cell-2 centre routes to cell 1, or build error).
+
+- [ ] **Step 3: GLFW host**
+
+In `glfw_host.cpp`: `set_figure` uses `plot_count()` for the controllers; `refresh_row_rects` copies `layout().cells`; replace `row_in(rows, y)` with
+
+```cpp
+static int row_in(const std::vector<Rect>& rects, double x, double y)
+{
+    int best = -1;
+    double best_d = 0.0;
+    for (std::size_t i = 0; i < rects.size(); ++i) {
+        const Rect& r = rects[i];
+        const double dx = x < r.x ? r.x - x : (x > r.right() ? x - r.right() : 0.0);
+        const double dy = y < r.y ? r.y - y : (y > r.bottom() ? y - r.bottom() : 0.0);
+        const double d = dx * dx + dy * dy;
+        if (best < 0 || d < best_d) { best = static_cast<int>(i); best_d = d; }
+        if (d == 0.0) break;
+    }
+    return best;
+}
+```
+
+(Use `r.y + r.h` / `r.x + r.w` if `Rect` has no `bottom()`.) For unsplit figures this is equivalent to the old y-only nearest-row rule. Make `controller_at(x, y)`, `pointer_target(x, y, ...)` and `pointer_row(rows)` pass `x` (use `last_pointer_x_` in `pointer_row`) and drop the `(void)x`. `sync_figure_crosshair` loops over the plot count. Update the header comments.
+
+- [ ] **Step 4: GTK adapter**
+
+In `gtk_plot_area.cpp`: `set_figure` uses `plot_count()` (line ~248); `refresh_row_rects` caches `.layout().cells`; add the same x-aware `row_in(rows, x, y)`; change `controller_at`, `row_at(x, y)` (use `to_device(x, y)`), `target_controller(f32 x, f32 y)`, `pointer_row()` (`pointer_.x/.y`) and `press_row_` (set with `row_in(row_rects_, p.x, p.y)` at ~619). Update every call site of `target_controller` (~637 `p`, ~646 `position`, ~751 `sample.position`, ~798 `g`, ~837 `at`, ~861 `p`) to pass both coordinates. Update the header declarations.
+
+- [ ] **Step 5: Build and run plotter tests**
+
+Run: `cmake --build deps/plotter/build 2>&1 | tail -5 && for t in deps/plotter/build/test_*; do $t >/dev/null || echo FAIL $t; done`
+Expected: no FAIL lines.
+
+- [ ] **Step 6: Commit the submodule, then the pin; check the app still builds**
+
+```bash
+git -C deps/plotter add -u && git -C deps/plotter commit -m "adapters: route pointer events by cell rect"
+git add deps/plotter && git commit -m "deps/plotter: figure rows can hold several plots"
+cmake --build build 2>&1 | grep -c warning
+```
+Expected: the build succeeds with the single baseline warning (count as before the change; compare with `git stash`-free run of an untouched clean build if unsure).
+
+---
+
+### Task 3: `RowSet` cell state and the split probe scaffold
+
+**Files:**
+- Modify: `src/plot_host.hpp`, `src/plot_host.cpp` (`rebuild_all` ~309, `set_row_count` ~156, `carry_row` ~164, `clear_row` ~184, `insert_row` ~195, `remove_row` ~205, `apply_row_weights` ~303, `x_note` caption ~920)
+- Modify: `src/ui_app.hpp` (`dbg_split_step`, declarations near ~2093), `src/ui_probe.cpp` (new `split_probe_*`), `src/ui.cpp` (scheduling next to `UDPSCOPE_PROBE_LAYOUT_MS`, ~6003)
+
+**Interfaces:**
+- Produces in `RowSet`:
+  - `static constexpr int kMaxCellsPerRow = 4;`
+  - `int figure_row_count() const; int cells_in_row(int fr) const; int first_plot_of_row(int fr) const; int figure_row_of(int plot) const /* -1 if invalid */; int cell_of(int plot) const; const std::vector<float>& cell_weights(int fr) const;`
+  - `std::string plot_label(int plot) const` ("2" for a single-cell row, "2a".."2d" for a split row; the figure row is `fr + 1`)
+  - `bool insert_cell(int fr, int at)`, `bool remove_cell(int plot)`, `void set_cell_weights(int fr, std::vector<float> w)`, `void set_cells_per_row(std::vector<int> cells)`
+  - `insert_row(at)` / `remove_row(at)` act on figure rows; `set_row_count(n)` means n single-cell rows; `row_count()` stays the plot count.
+- Invariant: `sum(cells_per_row_) == rows_` (rows_ ≤ kMaxRows = 8).
+
+- [ ] **Step 1: Read** `plot_host.hpp` 35–215, 280–320 and `plot_host.cpp` 135–345, 905–950 to see `carry_row`, `clear_row`, `storage_`, `rebuild_all`.
+
+- [ ] **Step 2: Header additions**
+
+```cpp
+static constexpr int kMaxCellsPerRow = 4;
+
+int figure_row_count() const { return static_cast<int>(cells_per_row_.size()); }
+int cells_in_row(int fr) const;
+int first_plot_of_row(int fr) const;          // rows_ for fr == figure_row_count()
+int figure_row_of(int plot) const;            // -1 if plot is out of range
+int cell_of(int plot) const;                  // 0-based position inside its row, -1 if invalid
+const std::vector<float>& cell_weights(int fr) const;
+std::string plot_label(int plot) const;
+
+bool insert_cell(int fr, int at);             // false at kMaxCellsPerRow cells or kMaxRows plots
+bool remove_cell(int plot);                   // a single-cell row removes the row; false if it would leave no plot
+void set_cell_weights(int fr, std::vector<float> w);
+void set_cells_per_row(std::vector<int> cells);
+
+private:
+    std::vector<int> cells_per_row_{1};
+    std::vector<std::vector<float>> cell_weights_ = std::vector<std::vector<float>>(1);
+    void apply_cell_weights();
+```
+
+- [ ] **Step 3: Implement queries and labels** in `plot_host.cpp`
+
+```cpp
+int RowSet::cells_in_row(int fr) const
+{
+    return fr >= 0 && fr < figure_row_count() ? cells_per_row_[fr] : 0;
+}
+int RowSet::first_plot_of_row(int fr) const
+{
+    int p = 0;
+    for (int r = 0; r < fr && r < figure_row_count(); ++r) p += cells_per_row_[r];
+    return p;
+}
+int RowSet::figure_row_of(int plot) const
+{
+    if (plot < 0 || plot >= rows_) return -1;
+    int p = 0;
+    for (int r = 0; r < figure_row_count(); ++r) {
+        p += cells_per_row_[r];
+        if (plot < p) return r;
+    }
+    return -1;
+}
+int RowSet::cell_of(int plot) const
+{
+    const int fr = figure_row_of(plot);
+    return fr < 0 ? -1 : plot - first_plot_of_row(fr);
+}
+const std::vector<float>& RowSet::cell_weights(int fr) const
+{
+    static const std::vector<float> none;
+    return fr >= 0 && fr < static_cast<int>(cell_weights_.size()) ? cell_weights_[fr] : none;
+}
+std::string RowSet::plot_label(int plot) const
+{
+    const int fr = figure_row_of(plot);
+    if (fr < 0) return std::to_string(plot + 1);
+    if (cells_per_row_[fr] == 1) return std::to_string(fr + 1);
+    return std::to_string(fr + 1) + static_cast<char>('a' + cell_of(plot));
+}
+```
+
+- [ ] **Step 4: Figure construction in `rebuild_all`**
+
+Replace the `std::make_unique<plot::Figure>(rows_)` with
+
+```cpp
+std::vector<plot::u32> cells(cells_per_row_.begin(), cells_per_row_.end());
+figure_ = std::make_unique<plot::Figure>(std::span<const plot::u32>(cells));
+```
+
+and after `set_row_gap(kRowGap)` add `figure_->set_col_gap(kColGap);` (`constexpr float kColGap = 6.0f;` beside `kRowGap`), then call `apply_row_weights(); apply_cell_weights();`. The per-plot loop stays per plot index (it already iterates `rows_`).
+
+```cpp
+void RowSet::apply_cell_weights()
+{
+    if (!figure_) return;
+    cell_weights_.resize(cells_per_row_.size());
+    for (int fr = 0; fr < figure_row_count(); ++fr) {
+        auto& w = cell_weights_[fr];
+        if (cells_per_row_[fr] < 2) { w.clear(); continue; }
+        if (w.empty()) { figure_->clear_cell_weights(fr); continue; }
+        w.resize(cells_per_row_[fr], 1.0f);
+        figure_->set_cell_weights(fr, std::span<const float>(w));
+    }
+}
+```
+
+`apply_row_weights` resizes to `figure_row_count()` instead of `rows_`.
+
+- [ ] **Step 5: Mutators**
+
+```cpp
+bool RowSet::insert_cell(int fr, int at)
+{
+    if (fr < 0 || fr >= figure_row_count()) return false;
+    if (cells_per_row_[fr] >= kMaxCellsPerRow || rows_ >= kMaxRows) return false;
+    const int n = cells_per_row_[fr];
+    const int p = first_plot_of_row(fr) + std::clamp(at, 0, n);
+    for (int i = rows_; i > p; --i) carry_row(i, i - 1);   // carry_row(dst, src), as insert_row uses it
+    clear_row(p);
+    ++rows_;
+    ++cells_per_row_[fr];
+    auto& w = cell_weights_[fr];
+    if (!w.empty()) {
+        float mean = 0.0f;
+        for (float v : w) mean += v;
+        mean /= static_cast<float>(w.size());
+        w.insert(w.begin() + std::clamp(at, 0, n), mean);
+    }
+    rebuild_all();
+    return true;
+}
+
+bool RowSet::remove_cell(int plot)
+{
+    const int fr = figure_row_of(plot);
+    if (fr < 0) return false;
+    if (cells_per_row_[fr] == 1) {
+        if (figure_row_count() == 1) return false;
+        remove_row(fr);
+        return true;
+    }
+    for (int i = plot; i + 1 < rows_; ++i) carry_row(i, i + 1);
+    --rows_;
+    clear_row(rows_);
+    const int k = plot - first_plot_of_row(fr);
+    --cells_per_row_[fr];
+    auto& w = cell_weights_[fr];
+    if (cells_per_row_[fr] < 2) w.clear();
+    else if (k < static_cast<int>(w.size())) w.erase(w.begin() + k);
+    rebuild_all();
+    return true;
+}
+
+void RowSet::set_cell_weights(int fr, std::vector<float> w)
+{
+    if (fr < 0 || fr >= figure_row_count()) return;
+    cell_weights_[fr] = std::move(w);
+    if (figure_) apply_cell_weights();
+}
+
+void RowSet::set_cells_per_row(std::vector<int> cells)
+{
+    std::vector<int> next;
+    int total = 0;
+    for (int c : cells) {
+        c = std::clamp(c, 1, kMaxCellsPerRow);
+        if (total + c > kMaxRows) c = kMaxRows - total;
+        if (c < 1) break;
+        next.push_back(c);
+        total += c;
+    }
+    if (next.empty()) next.push_back(1), total = 1;
+    cells_per_row_ = std::move(next);
+    cell_weights_.assign(cells_per_row_.size(), {});
+    rows_ = total;
+    rebuild_all();
+}
+```
+
+Check against the real `carry_row` signature (read in Step 1) and keep its argument order; if `insert_row` uses a different shifting idiom, copy it. `insert_row(at)` / `remove_row(at)`: `at` is a figure row; the plot position is `first_plot_of_row(at)`; insert/erase the matching `cells_per_row_` entry (one cell for an inserted row) and `cell_weights_` entry; `remove_row` shifts storage down by the removed row's cell count `n` and decrements `rows_` by `n`. `insert_row` refuses when `rows_ >= kMaxRows`. `set_row_count(n)`: sets all cells to one per row (`cells_per_row_.assign(n, 1)`, `cell_weights_.assign(n, {})`) and early-returns only when `n == rows_` and every row already has one cell.
+
+- [ ] **Step 6: The `x_note` caption** (~line 920): replace `const bool bottom = i == rows_ - 1;` with `const bool bottom = i >= first_plot_of_row(figure_row_count() - 1);`.
+
+- [ ] **Step 7: Probe scaffold**
+
+In `ui_app.hpp` add `int dbg_split_step = 0;` beside `dbg_layout_step` and declarations beside the layout probe's: `void split_probe_report(App& app, const char* tag); void split_probe_next(App& app); gboolean split_probe_step(gpointer data);`. In `ui_probe.cpp` (SPDX header already in the file) add, modelled on `layout_probe_*` (read `ui_probe.cpp` 3386–3471 and 3751–3890 first, reuse `enable_all_probe`'s channel assignment loop):
+
+```cpp
+void split_probe_report(App& app, const char* tag)
+{
+    RowSet& rs = *app.rows;
+    const auto& fl = rs.figure().layout();
+    int tile = 1;
+    for (int fr = 0; fr < rs.figure_row_count(); ++fr) {
+        const int first = rs.first_plot_of_row(fr), n = rs.cells_in_row(fr);
+        const auto& row = fl.rows[fr];
+        if (std::fabs(fl.cells[first].x - row.x) > 0.5f) tile = 0;
+        if (std::fabs(fl.cells[first + n - 1].right() - row.right()) > 0.5f) tile = 0;
+        for (int k = 0; k < n; ++k) {
+            const auto& c = fl.cells[first + k];
+            if (std::fabs(c.y - row.y) > 0.5f || std::fabs(c.h - row.h) > 0.5f) tile = 0;
+            if (k > 0 && std::fabs((c.x - fl.cells[first + k - 1].right()) - fl.col_gap) > 0.5f) tile = 0;
+        }
+    }
+    // x_equal: every plot's x range equals plot 0's; cursors_aligned: every plot's cursor a/b x equal
+    int x_equal = 1, aligned = 1;
+    const auto r0 = rs.plot(0)->x_range(rs.axis_x(0));
+    for (int p = 1; p < rs.row_count(); ++p) {
+        const auto r = rs.plot(p)->x_range(rs.axis_x(p));
+        const double span = std::max(1e-12, std::fabs(r0.hi - r0.lo));
+        if (std::fabs(r.lo - r0.lo) > 1e-9 * span || std::fabs(r.hi - r0.hi) > 1e-9 * span) x_equal = 0;
+        if (std::fabs(rs.cursor_x(p, 0) - rs.cursor_x(0, 0)) > 1e-9 * span) aligned = 0;
+        if (std::fabs(rs.cursor_x(p, 1) - rs.cursor_x(0, 1)) > 1e-9 * span) aligned = 0;
+    }
+    // print: [split-probe] %-14s plots=%d frows=%d cells=[a,b] widths=[logical px, | between rows] tile=%d x_equal=%d cursors_aligned=%d weights=[...] traces=[P:name,...|...]
+}
+```
+
+The accessor names `plot(p)`, `axis_x(p)` and `cursor_x(p, which)` are placeholders for the host's real accessors for the plot object, its x axis index and cursor A/B x (the layout probe and `RowSet::cursor_a_x()` show them: `r.plot->cursor(r.cursor_a).x`, `r.plot->x_range(r.axis_x)`); use those, adding a tiny `RowSet::cursor_x(int plot, int which)` if none exists. Fill in the print line with `g_print`/`std::printf` in the style of `layout_probe_report`, with widths in logical px (`cell.w / scale`), weights from `rs.cell_weights(fr)` and traces as `P:name` from the slot names the layout probe already prints.
+
+`split_probe_step` follows `layout_probe_step` (200 ms) but with 250 ms steps; after any structural change call `app.area->set_figure(&app.rows->figure()); app.relayout_pending = true;` and let a frame run before the report. Steps:
+  0. `rows->set_cells_per_row({1}); ` free the slots; enable all signals and assign channels via the `enable_all_probe` loop; report `"start"` (expect `plots=1 frows=1 cells=[1]`).
+  1. `insert_cell(0, 1)`; assign channel 0 to plot 0 and channel 1 to plot 1; `set_cursors_visible(true)`; report `"split"` (expect `cells=[2] tile=1 x_equal=1 cursors_aligned=1`).
+  2. `set_cell_weights(0, {3, 1})`; report `"weights 3:1"` (widths ratio about 3:1 after the floors; `tile=1`).
+  3. `insert_row(1)` then `insert_cell(1, 1)`; report `"row+cell"` (expect `cells=[2,2] plots=4`).
+  4. Call `insert_cell` until it returns false and then `insert_row` until the plot total is 8; report `"caps"` printing the refusals (`insert_cell(0, 2)` true, `…` false at 4 cells; `insert_row` false at 8 plots). Keep these as separate printed `refused=` fields.
+  5. `remove_cell` on the last plot of the widest row, report `"remove"`; then finish by returning `G_SOURCE_REMOVE`.
+
+In `ui.cpp` next to `UDPSCOPE_PROBE_LAYOUT_MS` (~6003) add:
+
+```cpp
+if (const char* ms = g_getenv("UDPSCOPE_PROBE_SPLIT_MS"))
+    g_timeout_add(static_cast<guint>(std::atoi(ms)), split_probe_step, app);
+```
+
+(Use the exact `g_timeout_add` argument shape the layout probe uses.)
+
+- [ ] **Step 8: Build and run the probe**
+
+```bash
+cmake --build build 2>&1 | grep -E 'warning|error' | head
+python3 tools/mock_udpstreamer.py --port 8171 --rate 1000 --batch 20 & MOCK=$!; sleep 2
+xvfb-run -a env UDPSCOPE_EXIT_AFTER_MS=6000 UDPSCOPE_PROBE_SPLIT_MS=1500 ./build/udpscope --server 127.0.0.1 --port 8171 2>&1 | grep -E 'split-probe|gtk warnings|Gtk-CRITICAL'
+kill $MOCK
+```
+Expected: the six `[split-probe]` lines above with `tile=1 x_equal=1 cursors_aligned=1`, `gtk warnings: 0`, no `Gtk-CRITICAL`. Also confirm that the first build output still has exactly one warning.
+
+- [ ] **Step 9: Commit**
+
+```bash
+git add src/plot_host.hpp src/plot_host.cpp src/ui_app.hpp src/ui_probe.cpp src/ui.cpp
+git commit -m "plot host: rows hold 1..4 cells; split probe scaffold"
+```
+
+---
+
+### Task 4: Session file and probe round-trip
+
+**Files:**
+- Modify: `src/layout_store.hpp` (`LayoutState::Row`), `src/layout_store.cpp` (writer ~786, `plots = N` ~729, parser `[[plot]]` ~457 and keys ~605–614, fallback ~718), `src/ui_layout.cpp` (`collect_layout` 17–36, `apply_layout` ~445–520)
+- Modify: `src/ui_probe.cpp` (new probe steps)
+
+**Interfaces:**
+- Consumes: `RowSet::cells_in_row`, `figure_row_of`, `cell_weights`, `set_cells_per_row`, `set_cell_weights`, `set_row_weights`.
+- Produces: `LayoutState::Row { …; int row = -1; double width = 1.0; }`.
+
+- [ ] **Step 1: Format**
+
+`LayoutState::Row` gains `int row = -1;  // figure row; -1 = file had none` and `double width = 1.0;  // cell weight`. The writer emits, per `[[plot]]`: `row = <fr>`, `width = <w>`, then the existing `weight` (the figure row's weight, written on every cell) and `signals`. Parser: keys `row` (int ≥ 0) and `width` (double > 0) next to `weight`. A file where no `[[plot]]` has `row` leaves every `row == -1`.
+
+- [ ] **Step 2: `collect_layout`** — for each plot `p`: `fr = rs.figure_row_of(p)`, `row.row = fr`, `row.weight = row_weights()[fr]`, `row.width = cell_weights(fr)` entry `cell_of(p)` or 1.0 when the row has no weights.
+
+- [ ] **Step 3: `apply_layout`** — before `set_row_count`: if every `Row.row >= 0`, validate that rows are non-decreasing, contiguous from 0 (each step 0 or +1), at most `kMaxCellsPerRow` cells per row and at most `kMaxRows` plots, otherwise fall back to the one-cell-per-row path. Valid: build `cells_per_row` counts and call `rows->set_cells_per_row(counts)`; row weights come from the first cell of each figure row (`set_row_weights`); for rows with ≥ 2 cells call `set_cell_weights(fr, {widths…})`. Fallback (no `row`, or invalid): `set_row_count(min(n, kMaxRows))` as today. The per-plot signal assignment loop is unchanged (it is per flattened plot index).
+
+- [ ] **Step 4: Probe steps** — append to `split_probe_step`: 
+  6. Build `{1,2}` with weights `{3,1}` and signals in each cell, `collect_layout` → `save_layout(tmp)` (use a path under `g_get_tmp_dir()` and delete it afterwards) → set to `{1}` → `load_layout` → `apply_layout`; report `"roundtrip"` and add `rt=1/0` comparing cells, widths (tolerance 1e-6) and traces.
+  7. Write a copy of that file with all `row = …` lines stripped, load/apply it, report `"legacy"` (expect `cells=[1,1,1]`, or the plot count of the file, one cell per row).
+
+- [ ] **Step 5: Run the probe** (same recipe as Task 3 Step 8). Expected: `roundtrip rt=1`, `legacy` with one cell per row, `gtk warnings: 0`.
+
+- [ ] **Step 6: Commit**
+
+```bash
+git add src/layout_store.hpp src/layout_store.cpp src/ui_layout.cpp src/ui_probe.cpp
+git commit -m "session: plots carry row and width; files without row load one cell per row"
+```
+
+---
+
+### Task 5: Layout editor cell controls and column drag
+
+**Files:**
+- Modify: `src/ui.cpp` (layout editor 568–807), `src/ui_layout.cpp` (534–598 handlers), `src/ui_app.hpp` (constants ~1600–1607, new `App` fields), `src/ui_probe.cpp` (`layout_probe_*` re-baseline, new split-probe click steps)
+
+**Interfaces:**
+- Consumes: Task 3 `RowSet` API, Task 2 `FigureLayout.cells`.
+- Produces: `void layout_col_apply(App&, int plot, double offset_px)`, `GtkWidget* layout_cell_button(App&, int fr, int pos)`, `GtkWidget* layout_col_handle(App&, int plot)`; `App::layout_col_drag_plot`, `App::layout_col_drag_left0` / `layout_col_drag_right0` (start widths, logical px); constants `kLayoutCellKey = "udpscope-layout-cell"`, `kLayoutColKey = "udpscope-layout-col"`, `kMinCellPx = 96`.
+
+- [ ] **Step 1: Read** `ui.cpp` 568–807 (overlay build, `sync_layout_editor`, `layout_overlay_button`), `ui_layout.cpp` 534–598 and the drag handlers, `ui_app.hpp` ~1600–1607.
+
+- [ ] **Step 2: Row-keyed controls by figure row.** The row boundary `+` buttons and the row resize handles are keyed by **figure row** (`figure_row_count() + 1` boundaries, positioned from `fl.rows`). `on_layout_row_insert(boundary)` calls `rows->insert_row(boundary)`. The per-cell `×` stays keyed by plot index (existing `set_row_key`), positioned from `fl.cells[idx]` top-left, and its handler calls `rows->remove_cell(idx)`; it is insensitive when `remove_cell` would fail (`row_count() == 1`). After each handler: `app->area->set_figure(&app->rows->figure())`, `rebuild_layout_editor`, `rebuild_signal_panels`, `schedule_layout_save` (same tail as the existing handlers). The row `+` is insensitive at `row_count() >= RowSet::kMaxRows`.
+
+- [ ] **Step 3: Cell `+` buttons.** For each figure row `fr` with `n = cells_in_row(fr)`, create `n + 1` buttons via `layout_overlay_button(app, "list-add-symbolic", tooltip)` with `g_object_set_data(btn, kLayoutCellKey, GINT_TO_POINTER(fr * 8 + pos + 1))` (do **not** call `set_row_key`). Positions: `pos 0` at `cells[first].x/scale + kLayoutButtonPad`; internal `pos k` centred on the gap between cells `k-1` and `k`; `pos n` at `cells[last].right()/scale - kLayoutButtonPx - kLayoutButtonPad`; vertically centred in `fl.rows[fr]`. Clicking calls `rows->insert_cell(fr, pos)` then the same tail as Step 2. Sensitivity: `cells_in_row(fr) < kMaxCellsPerRow && row_count() < kMaxRows`. Convert with `/scale` as the existing code does in `sync_layout_editor`, and re-place them in `sync_layout_editor` every frame.
+
+- [ ] **Step 4: Column resize handles.** At each internal boundary `k` (1..n-1) of a split row create a drag handle with `kLayoutColKey` = plot index of the right-hand cell (`first + k`), placed just right of the cell `+` there, with a left-right arrow icon (`go-next-symbolic` is acceptable, use whatever the row handle's icon pair provides for the horizontal direction), copying the row handle's `GtkGestureDrag` ("udpscope-layout-drag" pattern with its own begin/update/end handlers). Handlers:
+
+```cpp
+void layout_col_apply(App& app, int plot, double offset_px)
+{
+    RowSet& rs = *app.rows;
+    const int fr = rs.figure_row_of(plot);
+    const int k = rs.cell_of(plot);
+    if (fr < 0 || k < 1) return;
+    const double scale = gtk_widget_get_scale_factor(app.window) > 0 ? ui_scale_of(app) : 1.0;  // use the helper sync_layout_editor uses
+    const double pair = app.layout_col_drag_left0 + app.layout_col_drag_right0;
+    const double want_left = std::clamp(app.layout_col_drag_left0 + offset_px / scale, double(kMinCellPx), pair - kMinCellPx);
+    std::vector<float> w = rs.cell_weights(fr);
+    w.resize(rs.cells_in_row(fr), 1.0f);
+    const float sum = w[k - 1] + w[k];
+    w[k - 1] = static_cast<float>(sum * want_left / pair);
+    w[k]     = sum - w[k - 1];
+    rs.set_cell_weights(fr, w);
+    app.area->queue_draw();   // same redraw call the row drag uses
+}
+```
+
+`begin` records `layout_col_drag_plot = plot` and the logical widths `cells[plot-1].w/scale` and `cells[plot].w/scale`, and also snapshots `rs.cell_weights(fr)` (resized with 1.0) so repeated `update` calls are relative to drag start, as the row drag is. If the pair is narrower than `2 * kMinCellPx`, make the clamp degenerate to `pair / 2` rather than inverted bounds. `end` calls `schedule_layout_save(app)`.
+
+- [ ] **Step 5: Tooltips and sensitivity wording.** Cell `+`: "Split here"; column handle: "Drag to resize the plots"; `×` in a multi-cell row: "Remove this plot"; one-cell row: unchanged ("Remove this row").
+
+- [ ] **Step 6: Helpers for the probe.** `layout_cell_button(App&, fr, pos)` and `layout_col_handle(App&, plot)` find the widget by walking the overlay children and matching `kLayoutCellKey` / `kLayoutColKey` data (as `layout_button` does for `row_key`).
+
+- [ ] **Step 7: Probe steps.** Append to `split_probe_step`: with the layout editor open (reuse how `layout_probe_step` opens it), 8. click `layout_cell_button(app, 0, 1)` via `layout_click` → expect `cells=[2]`; 9. call `layout_col_apply` through the real handle's begin/update/end (or `layout_col_apply(app, 1, 80.0)` after setting the start widths as the begin handler does) → widths shift by 80 logical px and neither cell is below 96; a drag of ±10000 px clamps both to ≥ 96; 10. click the `×` of the new cell → `cells=[1]`; 11. report the sensitivity of the cell `+` at 4 cells in the row (`cell_plus_sensitive=0`) and of the row `+` at 8 plots.
+
+- [ ] **Step 8: Re-baseline the layout probe.** Run the existing `UDPSCOPE_PROBE_LAYOUT_MS` probe on the previous commit and on this one (fresh `XDG_CONFIG_HOME` per side) and diff number-normalised (`sed 's/[0-9.]\+/N/g'`). The only expected difference is the button count: `+2` per figure row (the two edge `+`s). Update the expected count in `docs/claude/probe-readings.md` in Task 8; do not change anything else in the baseline.
+
+- [ ] **Step 9: Build, run both probes** (`UDPSCOPE_PROBE_LAYOUT_MS` and `UDPSCOPE_PROBE_SPLIT_MS`, serially). Expected: split-probe lines as designed, `gtk warnings: 0`, no `Gtk-CRITICAL`.
+
+- [ ] **Step 10: Commit**
+
+```bash
+git add src/ui.cpp src/ui_layout.cpp src/ui_app.hpp src/ui_probe.cpp
+git commit -m "layout editor: split a row into cells, resize cells by drag"
+```
+
+---
+
+### Task 6: Signals page, notices and drop target
+
+**Files:**
+- Modify: `src/ui_signal_page.cpp` (~260–285), `src/ui_signals.cpp` (~557, ~570, ~579), `src/ui.cpp` (~325, ~1680, ~2762, ~2766, ~2942)
+
+**Interfaces:**
+- Consumes: `RowSet::plot_label(int)`, x-aware `area->row_at(x, y)` from Task 2.
+
+- [ ] **Step 1:** In `ui_signal_page.cpp` "Plot on" buttons keep their `udpscope-row` data (plot index) and the `assign_signal_to_row` callback but their label becomes `rows->plot_label(r)` and, for split rows, the tooltip "row 2, cell 1 of 2" (`"row %d, cell %d of %d"` with `figure_row_of + 1`, `cell_of + 1`, `cells_in_row`). This amends the spec's "row 2, left" wording to a unified numeric form; a single-cell row keeps its existing tooltip.
+- [ ] **Step 2:** Replace `"row %d"` / `r + 1` notices at `ui_signals.cpp:557`, `:570`, `ui.cpp:1680`, `:2762`, `:2766` with `"row %s"` and `plot_label(i).c_str()`.
+- [ ] **Step 3:** Confirm `row_at(app, x, y)` (`ui.cpp:325`) forwards `x` to `area->row_at` (it did not need it before) and that the two callers (`ui_signals.cpp:579`, `ui.cpp:2942`) pass the pointer position unchanged. Persistence layers (`sync_layers`) fill free slots of the same plot, with no change.
+- [ ] **Step 4:** Extend the split probe: after step 3 of Task 3, call `assign_signal_to_row` for a signal onto plot 1 of a split row and report the notice text / `traces=` showing the signal on `1b`. Expected probe line shows `traces=[…|1b:name…]`.
+- [ ] **Step 5:** Build, run the split probe and `gtk warnings: 0`; commit:
+
+```bash
+git add src/ui_signal_page.cpp src/ui_signals.cpp src/ui.cpp src/ui_probe.cpp
+git commit -m "signals: label plots by row and cell, drop onto a cell"
+```
+
+---
+
+### Task 7: Regression runs
+
+**Files:** none (verification); `docs/claude/probe-readings.md` is updated in Task 8 for any feature-explained difference.
+
+- [ ] **Step 1:** Clean build from scratch in a temporary build dir; expect exactly one warning.
+- [ ] **Step 2:** Serially run the probes listed in `docs/claude/verification.md` that touch layout, cursors, measurements, readouts and the E-1608 source (one mock per run, killed afterwards). For each, run once on the pre-feature commit (`git worktree` or checkout of `HEAD` before Task 1, built separately) and once now with a fresh `XDG_CONFIG_HOME`; diff number-normalised. The only acceptable differences are those the feature explains (layout probe's button count, new `cells`/column-weights lines in layout dumps).
+- [ ] **Step 3:** Layout dumps and probes that print per-row layout gain a `cells=[…]` list and a `colweights=[…]` line: add those to `layout_probe_report` and to the layout dump in `ui.cpp`, then re-run to confirm the numbers.
+- [ ] **Step 4:** Run the plotter suite once more (`deps/plotter/build`, all `test_*`).
+- [ ] **Step 5:** Commit any report-line additions: `git add src/ui_probe.cpp src/ui.cpp && git commit -m "probes: print cells and column weights"`.
+
+---
+
+### Task 8: Docs
+
+**Files:** `README.md`, `docs/USER-GUIDE.md`, `help/C/org.udpscope.app/` (layout page), `docs/claude/probe-readings.md`, `docs/claude/verification.md`, `docs/claude/invariants-plot-and-layout.md`, `docs/claude/build-and-run.md`, `src/ui_context_help.cpp`, `CLAUDE.md` (only if the "figure of up to eight stacked rows" sentence needs "plots").
+
+- [ ] **Step 1: Write each doc paragraph** (real text, in the style of the neighbouring sections):
+  - `build-and-run.md` (vendored plotter changes list): "`plot::Figure` rows can hold several plots: `Figure(std::span<const u32> cells_per_row)`, `plot_count()`, `cells_in_row()`, `first_plot_of_row()`, `row_of_plot()`, `set_cell_weights()`, `set_col_gap()`, `FigureLayout::cells`/`col_gap`. `Figure(u32 rows)` still means one cell per row. Cell widths use the height scheme with a 64 px (logical) floor; the GTK4 and GLFW adapters route pointer events by cell rect."
+  - `invariants-plot-and-layout.md` (cell rules): plots are indexed flat; `row_count()` is the plot count and `figure_row_count()` the rows; the x link, the crosshair and the vertical cursor pair are shared by all cells; y axes, horizontal rulers and fit are per cell; only the bottom row's cells carry x labels; the left gutter is one maximum for the whole figure; caps 4 cells per row / 8 plots; the editor's `+` and drag rules.
+  - `verification.md` and `probe-readings.md`: `UDPSCOPE_PROBE_SPLIT_MS`, each `[split-probe]` line, the reading it must give (`tile=1 x_equal=1 cursors_aligned=1`, `rt=1`, legacy file → one cell per row), and the new layout-probe button count / the `cells` and `colweights` fields.
+  - `README.md` and `docs/USER-GUIDE.md`: a "Splitting a row" subsection: Layout editor → `+` at a row's left/right edge or between cells; drag the arrow to resize; `×` removes a cell; all cells share one time window; limits; session `row`/`width` keys.
+  - Mallard layout page and `ui_context_help.cpp` layout-editor text: the same user-facing paragraph, in the page's format.
+- [ ] **Step 2:** Build (the help page is validated at build/install, if the project has a `yelp-check` target run it) and run the context-help probe if `verification.md` lists one.
+- [ ] **Step 3: Commit**
+
+```bash
+git add README.md docs/USER-GUIDE.md help docs/claude src/ui_context_help.cpp CLAUDE.md
+git commit -m "docs: horizontal plot split"
+```
+
+---
+
+## Self-Review
+
+- **Spec coverage:** shared time window (Task 1 x link test, Task 3 probe `x_equal`); per-row 1..4 cells and caps (Tasks 3, 5); draggable widths saved (Tasks 4, 5); plotter API and layout rules including narrow degradation, bottom-only labels, common gutter (Task 1); hit-testing by cell (Task 2); host model, flattened indices, caps, cursors/crosshair/y axes per cell (Tasks 1, 3); drop onto a cell and "place on row" listing (Task 6, tooltip wording amended to "row 2, cell 1 of 2"); layout editor controls (Task 5); session format and legacy loading (Task 4); verification probes and regression (Tasks 3–5, 7); docs list (Task 8).
+- **Placeholders:** accessor names that the plan could not confirm without re-reading code (`layout_info()`, `rs.plot(p)`, `axis_x`, `cursor_x`, `carry_row` argument order, `Status` constructors) are flagged where used with how to resolve them from the neighbouring code; no behaviour is left unspecified.
+- **Type consistency:** `insert_cell(fr, at)`, `remove_cell(plot)`, `set_cell_weights(fr, vector<float>)`, `set_cells_per_row(vector<int>)`, `plot_label(plot)`, `figure_row_count()`, `cells_in_row(fr)`, `first_plot_of_row(fr)`, `figure_row_of(plot)`, `cell_of(plot)` are used with the same signatures in Tasks 3–6; plotter names (`plot_count`, `cells_in_row`, `set_cell_weights(u32, span<const f32>)`, `set_col_gap`, `FigureLayout::cells/col_gap`) match across Tasks 1–3.

docs/superpowers/plans/2026-11-03-split-shared-y.md

@@ -0,0 +1,342 @@
+# Split rows share one y axis -- Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** The cells of a split row share one y range and one y axis (labels on the leftmost cell only), as the figure's rows share one x window and one x axis.
+
+**Architecture:** The vendored plotter's `Figure` gets `set_share_row_y(bool)`: when on, every figure row with more than one cell keeps its cells' y axis 0 in step (range and auto flag) from `Figure::layout()`, and every cell but the first loses its y gutter (`YStrip::None`). The host turns it on in `RowSet::rebuild_all()`, mirrors the ruler pair across a row, and maps the layout editor's divider drag through plot widths.
+
+**Tech Stack:** C++20, GTK4/libadwaita, the vendored `deps/plotter` (git submodule; commit inside it first, then the pin in the main repo), headless probes under `xvfb-run`.
+
+Spec: `docs/superpowers/specs/2026-11-03-split-shared-y-design.md` (amends `2026-11-03-horizontal-split-design.md`).
+
+## Global Constraints
+
+- Shared y is always on for split rows, no option; an unsplit row behaves exactly as before. (spec Decisions 1)
+- Only the leftmost cell of a row has a y gutter and y labels; the choice is structural (column index), never from content. (Decisions 2; "layout must not depend on content", `docs/claude/invariants-plot-and-layout.md`)
+- `Figure::set_share_row_y` defaults to off so existing figures and every existing test in `deps/plotter/tests` are unchanged.
+- Cell rects still tile the row exactly (last cell closes the row); no rect is ever negative; `Figure(u32 rows)` and `{1}` rows lay out as today.
+- The row's y gutter is taken off the row width first; the cells then share the rest by the existing `floor + extra*w/total` rule (floor `kMinCellWidthLogical = 64` x ui_scale), so equal weights give equal plot areas. The first cell's rect is gutter + its plot width.
+- Rulers: one pair per figure row, drawn at the same y in every cell; a drag in any cell moves them. Measure level marks, readouts, measurements stay per trace / per plot index.
+- Session file unchanged (y ranges were never persisted).
+- Every source file carries the SPDX MIT header (existing files already do).
+- Verification is by the plotter suite and the app's headless probes only. Build: exactly 1 warning (baseline). Probes: `gtk warnings: 0`, no `Gtk-CRITICAL`. Run recipe in `docs/claude/verification.md`; use a fresh throwaway `XDG_CONFIG_HOME` per run (never write `~/.config/udpscope`); run probes short and serial; kill the mock afterwards. The plotter test `staging_a_glyph_that_is_not_the_cell_aborts_in_a_debug_build` may hang: run the suite under `ulimit -c 0; timeout 300`.
+
+---
+
+## File map
+
+| File | Change |
+| --- | --- |
+| `deps/plotter/include/plot/plot/plot.hpp`, `src/plot/plot.cpp` | `YStrip`, `set_y_strip_mode`, `set_y_link_member`, `y_data_bounds`, `fit_y_bounds`; skip autoscale of a linked y axis; zero y chrome for `YStrip::None` |
+| `deps/plotter/include/plot/plot/figure.hpp`, `src/plot/figure.cpp` | `set_share_row_y`, `row_y_auto`, `sync_row_y()`, strip modes, gutter maximum over leftmost cells, plot-width cell placement |
+| `deps/plotter/src/render/renderer.cpp` (+ adapters if needed) | no y labels for a `None` cell |
+| `deps/plotter/tests/test_figure.cpp` | new cases |
+| `src/plot_host.cpp`, `src/ui.cpp`, `src/ui_cursors.cpp`, `src/ui_probe.cpp` | host wiring, rulers, pane, drag, probes |
+| docs | see Task 5 |
+
+---
+
+### Task 1: Plotter -- y link of a row's cells (range and auto)
+
+**Files:**
+- Modify: `deps/plotter/include/plot/plot/plot.hpp`, `deps/plotter/src/plot/plot.cpp`
+- Modify: `deps/plotter/include/plot/plot/figure.hpp`, `deps/plotter/src/plot/figure.cpp`
+- Test: `deps/plotter/tests/test_figure.cpp`
+
+**Interfaces:**
+- Produces (Plot): `void set_y_link_member(u32 axis, bool linked) noexcept;` `bool y_data_bounds(u32 axis, Range& out) const;` (union of the visible traces' y bounds on that axis, false if none) `bool fit_y_bounds(u32 axis, Range bounds);` (the axis' own padded fit of `bounds`, as `fit_y_axis` does; leaves `auto_scale` alone).
+- Produces (Figure): `void set_share_row_y(bool on);` `bool share_row_y() const noexcept;` `bool row_y_auto(u32 row) const noexcept;` (figure row; true for a row with fewer than two cells or when sharing is off, i.e. "no group").
+- Behaviour: with sharing on, for each figure row with `n > 1` cells, y axis 0 of its cells is one group. A range set on any member (wheel, drag, `set_y_range`) becomes the group's and is pushed to all; the group is auto or manual as one; auto fits the union of all members' visible traces (cells without a trace ignored; padding/log handling is `fit_axis_range`'s, via `fit_y_bounds` on the first member). Members' own autoscale is suppressed.
+
+Group state per row (`Figure::RowY`): `Range pushed; bool have = false; bool auto_scale = true;`. Sync, run from `Figure::layout()` right after `sync_x_links()` (before any `Plot::layout()` call, because that is where a plot would otherwise autoscale):
+
+```cpp
+void Figure::sync_row_y() {
+  if (!share_row_y_) return;
+  row_y_.resize(cells_per_row_.size());
+  for (u32 row = 0; row < cells_per_row_.size(); ++row) {
+    const u32 n = cells_per_row_[row];
+    if (n < 2u) continue;
+    RowY& g = row_y_[row];
+    const u32 first = row_first_[row];
+    if (!g.have) {
+      g.pushed = plots_[first].y_axis(0).range;
+      g.auto_scale = plots_[first].y_axis(0).auto_scale;
+    }
+    // What happened since the last push. A member's auto flag that differs from the group's is a
+    // request (set_y_range clears it, auto_fit_y / set_y_auto_scale(true) sets it); otherwise a
+    // member whose range differs from the pushed one was moved by a gesture.
+    bool want_auto = g.auto_scale;
+    Range target = g.pushed;
+    bool flag_request = false;
+    for (u32 i = first; i < first + n && !flag_request; ++i) {
+      const Axis& a = plots_[i].y_axis(0);
+      if (a.auto_scale != g.auto_scale) {
+        want_auto = a.auto_scale;
+        if (!want_auto) target = a.range;  // auto -> manual: the gesture's range
+        flag_request = true;
+      }
+    }
+    if (!flag_request && !want_auto) {
+      for (u32 i = first; i < first + n; ++i) {
+        const Range r = plots_[i].y_axis(0).range;
+        if (r.min != g.pushed.min || r.max != g.pushed.max) { target = r; break; }
+      }
+    }
+    if (want_auto) {
+      Range bounds{};
+      bool any = false;
+      for (u32 i = first; i < first + n; ++i) {
+        Range b{};
+        if (!plots_[i].y_data_bounds(0, b)) continue;
+        bounds = any ? Range{std::min(bounds.min, b.min), std::max(bounds.max, b.max)} : b;
+        any = true;
+      }
+      if (any && plots_[first].fit_y_bounds(0, bounds)) target = plots_[first].y_axis(0).range;
+      // else: nothing to fit -- keep the range the group had
+    }
+    for (u32 i = first; i < first + n; ++i) {
+      plots_[i].set_y_range(0, target);            // clears the flag ...
+      plots_[i].set_y_auto_scale(0, want_auto);    // ... so restate it: every member mirrors the group
+    }
+    g.pushed = target;
+    g.auto_scale = want_auto;
+    g.have = true;
+  }
+}
+```
+
+`set_share_row_y(on)` stores the flag, clears `row_y_`, and calls `set_y_link_member(0, on)` on every cell of every row with `n > 1` (cells whose plot has no y axis yet are fine: `set_y_link_member` ignores a missing axis, so also re-apply in `sync_row_y()` before the loop so axes added after the call are covered). `Plot::autoscale_axes()` must skip a y axis whose `link_member` is set (reuse `Axis::link_member`, currently x-only in meaning; update its comment). `y_data_bounds` is `trace_bounds_union(false, axis, out)`. `fit_y_bounds` is `return axis < y_axes_.size() && fit_axis_range(y_axes_[axis], bounds);`.
+
+- [ ] **Step 1: Write the failing tests** -- append to `deps/plotter/tests/test_figure.cpp` (they use the existing `split_figure`, `whole_figure`, `plot::data::ArraySeries`):
+
+```cpp
+PLOT_TEST(figure_row_y_cells_share_a_range_after_a_gesture) {
+  plot::Figure figure = split_figure({2, 1});
+  figure.set_share_row_y(true);
+  figure.layout();
+  figure.plot(1u).set_y_range(0u, {-3.0, 7.0});  // what a wheel / drag / pan ends in
+  figure.layout();
+  PLOT_CHECK_NEAR(figure.plot(0u).y_range(0u).min, -3.0, 1e-9);
+  PLOT_CHECK_NEAR(figure.plot(0u).y_range(0u).max, 7.0, 1e-9);
+  PLOT_CHECK_NEAR(figure.plot(1u).y_range(0u).min, -3.0, 1e-9);
+  PLOT_CHECK_NEAR(figure.plot(1u).y_range(0u).max, 7.0, 1e-9);
+  // The unsplit row is its own thing.
+  PLOT_CHECK_NEAR(figure.plot(2u).y_range(0u).min, -1.0, 1e-9);
+  PLOT_CHECK(!figure.row_y_auto(0u));
+}
+
+PLOT_TEST(figure_row_y_auto_fits_the_union_and_ignores_empty_cells) {
+  plot::Figure figure = split_figure({3});
+  for (plot::u32 i = 0; i < 3u; ++i) figure.plot(i).set_y_auto_scale(0u, true);
+  plot::data::ArraySeries a(std::vector<plot::f32>{0.0f, 10.0f, 5.0f}, 0.0, 1.0);
+  plot::data::ArraySeries b(std::vector<plot::f32>{-20.0f, 5.0f, 0.0f}, 0.0, 1.0);
+  figure.plot(0u).add_trace({&a, plot::Color::hex(0x40C0FF), 1.5f, 0u, 0u});
+  figure.plot(1u).add_trace({&b, plot::Color::hex(0xFF8080), 1.5f, 0u, 0u});
+  figure.set_share_row_y(true);  // cell 2 has no trace
+  figure.layout();
+  PLOT_CHECK(figure.row_y_auto(0u));
+  const plot::Range r0 = figure.plot(0u).y_range(0u);
+  PLOT_CHECK(r0.min <= -20.0 && r0.max >= 10.0);
+  PLOT_CHECK(r0.max - r0.min < 40.0);  // padded, not blown up
+  for (plot::u32 i = 1; i < 3u; ++i) {
+    PLOT_CHECK_NEAR(figure.plot(i).y_range(0u).min, r0.min, 1e-9);
+    PLOT_CHECK_NEAR(figure.plot(i).y_range(0u).max, r0.max, 1e-9);
+  }
+}
+
+PLOT_TEST(figure_row_y_manual_then_fit_returns_to_auto) {
+  plot::Figure figure = split_figure({2});
+  for (plot::u32 i = 0; i < 2u; ++i) figure.plot(i).set_y_auto_scale(0u, true);
+  plot::data::ArraySeries a(std::vector<plot::f32>{0.0f, 10.0f}, 0.0, 1.0);
+  plot::data::ArraySeries b(std::vector<plot::f32>{-4.0f, 4.0f}, 0.0, 1.0);
+  figure.plot(0u).add_trace({&a, plot::Color::hex(0x40C0FF), 1.5f, 0u, 0u});
+  figure.plot(1u).add_trace({&b, plot::Color::hex(0xFF8080), 1.5f, 0u, 0u});
+  figure.set_share_row_y(true);
+  figure.layout();
+  figure.plot(1u).set_y_range(0u, {1.0, 2.0});
+  figure.layout();
+  PLOT_CHECK(!figure.row_y_auto(0u));
+  PLOT_CHECK_NEAR(figure.plot(0u).y_range(0u).min, 1.0, 1e-9);
+  PLOT_CHECK_NEAR(figure.plot(0u).y_range(0u).max, 2.0, 1e-9);
+  figure.layout();  // manual holds: no fight with the plots' own autoscale
+  PLOT_CHECK_NEAR(figure.plot(1u).y_range(0u).max, 2.0, 1e-9);
+  figure.plot(0u).auto_fit_y(0u);  // what fit-all / double-click does to one cell
+  figure.layout();
+  PLOT_CHECK(figure.row_y_auto(0u));
+  PLOT_CHECK(figure.plot(1u).y_range(0u).min <= -4.0 && figure.plot(1u).y_range(0u).max >= 10.0);
+  PLOT_CHECK_NEAR(figure.plot(0u).y_range(0u).min, figure.plot(1u).y_range(0u).min, 1e-9);
+}
+
+PLOT_TEST(figure_row_y_sharing_off_keeps_cells_independent) {
+  plot::Figure figure = split_figure({2});
+  figure.layout();
+  figure.plot(1u).set_y_range(0u, {-3.0, 7.0});
+  figure.layout();
+  PLOT_CHECK_NEAR(figure.plot(0u).y_range(0u).max, 1.0, 1e-9);
+  PLOT_CHECK(!figure.share_row_y());
+}
+```
+
+- [ ] **Step 2: Run -- expect compile failure** (`set_share_row_y` undeclared). Build and run the plotter tests per `docs/claude/build-and-run.md` (the plotter's own CMake test target; run the binary with `ulimit -c 0; timeout 300`).
+- [ ] **Step 3: Implement** the Plot additions, `Figure` members (`bool share_row_y_ = false; struct RowY {...}; std::vector<RowY> row_y_;`), `set_share_row_y`, `share_row_y`, `row_y_auto` (`row < row_y_.size() && row_y_[row].have ? row_y_[row].auto_scale : true`), `sync_row_y` as above (declare it private next to `sync_x_links`), and call `sync_row_y();` in `Figure::layout()` immediately after `sync_x_links();`. Doc comments in the file's style (what, and why the group, not the plot, owns auto scale).
+- [ ] **Step 4: Run the whole plotter suite.** Expect all new cases pass and 0 failed overall (was 407 cases).
+- [ ] **Step 5: Commit** inside the submodule: `git -C deps/plotter add -u && git -C deps/plotter commit -m "figure: cells of a row can share one y range"`. Do not touch the pin yet.
+
+---
+
+### Task 2: Plotter -- one y axis per row (strip mode, gutter, cell widths)
+
+**Files:**
+- Modify: `deps/plotter/include/plot/plot/plot.hpp`, `deps/plotter/src/plot/plot.cpp` (`Plot::layout`, ~lines 1286-1390)
+- Modify: `deps/plotter/src/plot/figure.cpp` (`Figure::layout`, ~lines 550-625)
+- Modify: `deps/plotter/src/render/renderer.cpp` (~lines 900-920, y label staging)
+- Test: `deps/plotter/tests/test_figure.cpp`
+
+**Interfaces:**
+- Consumes: Task 1's `set_share_row_y`.
+- Produces: `enum class YStrip { Both, None };` next to `XStrip` in `plot.hpp`; `Plot::set_y_strip_mode(YStrip)` / `y_strip_mode()`. With `None`, `Plot::layout()` reserves no y label width and no y title width (`y_axis_width == 0`, `y_title_width == 0`, `y_label_area.w == 0`) and ignores `min_y_gutter_`; the grid lines are still built. With sharing on, `Figure::layout()` sets `None` on every cell but the first of its row; the common-gutter maximum is taken over `Both` cells only; `None` cells get `set_min_y_gutter(0)`.
+- Cell widths with sharing on, for a row with `n > 1` cells: after the gutter `G` is known (end of the measurement pass), `G_eff = min(G, row.w / 2)`; call `place_cells` on the rect `{row.x + G_eff, row.y, row.w - G_eff, row.h}`, then grow cell 0 to the left by `G_eff` (`x -= G_eff; w += G_eff`). Update `layout_.cells`, call `set_viewport` on each cell, then run the final `p.layout()` pass. With sharing off nothing changes.
+
+- [ ] **Step 1: Write the failing tests** (append to `test_figure.cpp`; `give_magnitude_row` and `split_figure` exist):
+
+```cpp
+PLOT_TEST(figure_row_y_only_the_first_cell_has_a_gutter) {
+  plot::Figure figure = split_figure({1, 3}, false);
+  for (plot::u32 i = 0; i < figure.plot_count(); ++i) give_magnitude_row(figure.plot(i), 0u);
+  figure.set_share_row_y(true);
+  figure.layout();
+  PLOT_CHECK(figure.plot(0u).layout().y_axis_width > 0.0f);   // unsplit row keeps its axis
+  PLOT_CHECK(figure.plot(1u).layout().y_axis_width > 0.0f);   // first cell of the split row
+  for (plot::u32 i = 2; i < 4u; ++i) {
+    const plot::PlotLayout& l = figure.plot(i).layout();
+    PLOT_CHECK(l.y_axis_width == 0.0f && l.y_title_width == 0.0f && l.y_label_area.w == 0.0f);
+    PLOT_CHECK(l.axes.w > 0.0f);
+  }
+  // The gutter is one figure-wide value: the unsplit row and the split row's first cell agree.
+  PLOT_CHECK_NEAR(figure.plot(0u).layout().axes.x - figure.layout().cells[0].x,
+                  figure.plot(1u).layout().axes.x - figure.layout().cells[1].x, 0.01);
+}
+
+PLOT_TEST(figure_row_y_equal_weights_give_equal_plot_widths_and_cells_tile) {
+  plot::Figure figure = split_figure({3}, false);
+  for (plot::u32 i = 0; i < 3u; ++i) give_magnitude_row(figure.plot(i), 0u);
+  figure.set_col_gap(8.0f);
+  figure.set_share_row_y(true);
+  const plot::FigureLayout& fl = figure.layout();
+  const double w0 = figure.plot(0u).layout().axes.w;
+  PLOT_CHECK_NEAR(figure.plot(1u).layout().axes.w, w0, 0.6);
+  PLOT_CHECK_NEAR(figure.plot(2u).layout().axes.w, w0, 0.6);
+  PLOT_CHECK_NEAR(fl.cells[0].x, fl.rows[0].x, 0.001);
+  PLOT_CHECK_NEAR(fl.cells[2].right(), fl.rows[0].right(), 0.001);
+  PLOT_CHECK_NEAR(fl.cells[1].x - fl.cells[0].right(), 8.0, 0.01);
+  PLOT_CHECK_NEAR(fl.cells[2].x - fl.cells[1].right(), 8.0, 0.01);
+}
+
+PLOT_TEST(figure_row_y_weights_apply_to_plot_widths) {
+  plot::Figure figure = split_figure({2}, false);
+  for (plot::u32 i = 0; i < 2u; ++i) give_magnitude_row(figure.plot(i), 0u);
+  figure.set_col_gap(0.0f);
+  figure.set_share_row_y(true);
+  const std::vector<plot::f32> w{3.0f, 1.0f};
+  PLOT_CHECK(figure.set_cell_weights(0u, w));
+  figure.layout();
+  const double a0 = figure.plot(0u).layout().axes.w;
+  const double a1 = figure.plot(1u).layout().axes.w;
+  PLOT_CHECK_NEAR(a0 - 64.0, (a1 - 64.0) * 3.0, 1.0);
+}
+
+PLOT_TEST(figure_row_y_narrow_row_degrades_without_negative_rects) {
+  plot::Figure figure = split_figure({4}, false);
+  figure.set_viewport(plot::Rect{0.0f, 0.0f, 30.0f, 100.0f});
+  for (plot::u32 i = 0; i < 4u; ++i) give_magnitude_row(figure.plot(i), 0u);
+  figure.set_col_gap(10.0f);
+  figure.set_share_row_y(true);
+  double sum = 0.0;
+  for (const plot::Rect& c : figure.layout().cells) {
+    PLOT_CHECK(c.w >= 0.0f && c.h >= 0.0f);
+    sum += c.w;
+  }
+  PLOT_CHECK_NEAR(sum, 30.0, 0.05);
+}
+
+PLOT_TEST(figure_row_y_sharing_off_still_gives_every_cell_a_gutter) {
+  plot::Figure figure = split_figure({2}, false);
+  give_magnitude_row(figure.plot(0u), 0u);
+  give_magnitude_row(figure.plot(1u), 1u);
+  figure.layout();
+  PLOT_CHECK(figure.plot(1u).layout().y_axis_width > 0.0f);
+}
+```
+
+Plus a renderer check: find how existing tests count or inspect staged text (see `tests/test_render_smoke.cpp` / the `staging_a_glyph_...` neighbourhood). Add one case that a `None` cell stages no y tick labels (the staged label count of a two-cell shared row equals that of a one-cell row of the same height, plus nothing for the second cell's y side). If the harness cannot observe staged text, instead assert in the renderer change below with a comment and report that no automated check was possible.
+
+- [ ] **Step 2: Run -- expect failures** (the gutter/width cases; `YStrip` undeclared).
+- [ ] **Step 3: Implement.**
+  - `Plot::layout`: `const bool y_none = y_strip_ == YStrip::None;` seed `y_width = y_none ? 0 : ...`, `y_title_w = y_none ? 0 : ...`, `y_floor = y_none ? 0 : min(min_y_gutter_, y_budget)`, and `need_y = y_none ? 0 : ...` in the fixed-point test so the loop still settles in two passes. Read the loop first; every use of the y strip widths must collapse to 0 and the `axes` must start at `viewport_.x`.
+  - `Figure::layout`: before the viewport loop compute `const bool shared = share_row_y_ && cells_per_row_[row] > 1u;` and set `p.set_y_strip_mode(shared && i != row_first_[row] ? YStrip::None : YStrip::Both)` (reset to `Both` when not shared). In the gutter maximum loop skip `None` plots and give them `set_min_y_gutter(0.0f)`. After the measurement pass and before the final `p.layout()` loop, re-place the cells of each shared row as specified in Interfaces and re-apply `set_viewport`.
+  - Renderer: do not stage y tick labels (and y title) when the plot's `layout().y_label_area.w <= 0.0f`; read the staging code at `renderer.cpp:~906-917` first. Check `src/input/controller.cpp:~524` still cannot start a y axis-drag in a zero-width label area (it hit-tests `y_label_area`); if it can, guard it.
+  - Check both adapters (`adapters/gtk4`, `adapters/glfw`) route by cell rect only, so nothing else changes.
+- [ ] **Step 4: Run the whole plotter suite.** Expect 0 failed, including all pre-existing figure cases (`figure_cells_common_y_gutter` still reads the old behaviour because sharing defaults off).
+- [ ] **Step 5: Commit** in the submodule: `git -C deps/plotter add -u && git -C deps/plotter commit -m "figure: shared-y rows draw one y axis, on the first cell"`. Then in the main repo: `git add deps/plotter && git commit -m "pin deps/plotter: shared y axis for split rows"`.
+
+---
+
+### Task 3: Host -- turn sharing on; rulers per row; pane and units
+
+**Files:**
+- Modify: `src/plot_host.cpp` (`rebuild_all`, `sync_cursors`, `place_cursors` call sites), `src/plot_host.hpp` if a helper is declared
+- Modify: `src/ui.cpp` (`row_unit` ~1759, cursors-pane line construction ~1840-1855), `src/ui_cursors.cpp` (~55-70)
+- Modify: `src/ui_probe.cpp` (split probe: new steps), `src/ui_app.hpp` if a probe state is needed
+- Test: the split probe (`UDPSCOPE_PROBE_SPLIT_MS`), layout probe
+
+**Interfaces:**
+- Consumes: Task 2's `Figure::set_share_row_y(bool)` and its pin.
+- Produces: no new public host API required. Behaviour: after `rebuild_all()` every split figure row shares y; `RowSet::set_y_auto/set_y_range/fit_all` need no change (they call per-plot setters that the figure's sync turns into row-wide effects).
+
+- [ ] **Step 1: Probe first (RED).** Add a new split-probe step after the existing steps (follow the existing step style in `ui_probe.cpp` near the `[split-probe] ...` lines; note the next free step index) that, on a figure with a split row holding a trace in each cell:
+  1. `y_shared`: set the y range on cell A via `rs.set_y_range(a, -3, 7)`, pump a frame, assert cell B's `plot->y_range(axis_y)` equals it.
+  2. `y_gutter`: cell B (non-first) `layout().y_axis_width == 0` and `y_label_area.w == 0`; cell A `> 0`; and `axes.w` of A and B equal within 1 px with default weights.
+  3. `y_fit`: `rs.fit_all()` then one frame: both cells' ranges equal and cover both traces' y bounds.
+  4. `ruler_mirror`: with cursor mode showing rulers, set cell A's ruler (via `set_cursor_y` on its plot) then call `rs.sync_cursors(a)`; `ruler_y(a)==ruler_y(b)` and `ruler_b_y` likewise.
+  Print one line: `[split-probe] shared-y        y_shared=%d y_gutter=%d y_fit=%d ruler_mirror=%d ranges=[...] axes_w=[..]`. Build and run it; expect `y_shared=0 y_gutter=0` (sharing not wired) -- RED.
+- [ ] **Step 2: Wire it.**
+  - `RowSet::rebuild_all()`: call `figure_->set_share_row_y(true);` right after the `Figure` is created (before `install`, so the axes added by `install` are picked up -- Task 1 re-applies membership in `sync_row_y`).
+  - `RowSet::sync_cursors(int drag_row)`: after `r.ruler_y/ruler_b_y` are read back from the dragged cell, copy both values to every other cell of the same figure row (`first_plot_of_row(figure_row_of(drag_row))` .. `+ cells_in_row`) and `place_cursors(that, plot::CursorPlacement::Free)` on them.
+  - `reset_cursors()` already writes each plot's rulers from its y range; confirm both cells of a row get identical values (the range is shared). Rulers that exist before the row was split: when `insert_cell` creates the new cell, copy the row's first cell's `ruler_y/ruler_b_y` into it (read `insert_cell` and `copy`/reset helpers near `plot_host.cpp:224-240`).
+  - Cursors pane (`ui.cpp:~1840`): the ruler line (`slot = -1`) is created once per figure row, for the row's first plot only (`app.rows->cell_of(r) == 0`). Label: unsplit rows keep today's wording; a split row uses `"row N"` with the same numbering `plot_label` uses for the row (without the cell letter). Check `ui_cursors.cpp:~60` and every other reader of `cursors_lines` / `slot == -1` for assumptions of one ruler line per plot, and update the probe line `ruler-labels` accordingly (its expected value changes by design -- say so in the report).
+  - `row_unit(app, row)` (`ui.cpp:~1759`): join the units over every cell of `row`'s figure row (loop `first_plot_of_row .. + cells_in_row`, same lock), "" if they differ.
+  - `sync_compare_axes` (`ui_events.cpp:~555`): leave as is; the probe in Step 3 includes a comparison-mode check only if the existing compare probe covers split rows, otherwise note it in the report as unverified.
+  - `ui.cpp:~4237` gutter reading takes a max over all plots and `~4361` reads plot 0: both stay correct (None cells read 0). Confirm by reading, change nothing.
+- [ ] **Step 3: Verify.** Incremental `cmake --build build` (1 warning baseline). Run the split probe and the layout probe per `docs/claude/verification.md` and diff against the baseline commit `18b91c8`-era numbers as in the earlier tasks (number-normalised): only lines this feature explains may differ (`ruler-labels`, `buttons=` unchanged, `cells=` unchanged; widths of non-first cells grow by the gutter). Expect the new line `y_shared=1 y_gutter=1 y_fit=1 ruler_mirror=1`, all earlier split-probe steps still reading as before (col-drag may change -- that is Task 4), `gtk warnings: 0`, no `Gtk-CRITICAL`.
+- [ ] **Step 4: Commit** `git add src/plot_host.cpp src/plot_host.hpp src/ui.cpp src/ui_cursors.cpp src/ui_probe.cpp src/ui_app.hpp && git commit -m "plot host: split rows share y, rulers per row"` (add only files actually changed).
+
+---
+
+### Task 4: Layout editor -- divider drag through plot widths
+
+**Files:**
+- Modify: `src/ui.cpp` (`layout_col_drag_begin` ~786, `layout_col_apply` ~755)
+- Modify: `src/ui_probe.cpp` (the `col-drag` step ~4190-4250), `src/ui_app.hpp` (`layout_col_drag_left0/right0` docs)
+- Test: split probe `col-drag` line
+
+**Interfaces:**
+- Consumes: Tasks 2-3. A cell's rect width is no longer its weight's width: weights apply to **plot widths** (`plot->layout().axes.w + right_gutter`, i.e. rect width minus the y gutter, which only cell 0 has).
+- Produces: `layout_col_drag_begin` stores the left/right **plot** widths in logical px (rect width minus `y_axis_width + y_title_width` of that cell's plot; the right cell's is 0). `layout_col_apply` is unchanged otherwise: the 96 px floor and the 64 px plotter floor both refer to plot widths now (`kMinCellPx`, `kPlotterMinCellPx`), the formula `frac = (want_left - 64)/(pair - 128)` stays, and the pair's weight sum stays.
+
+- [ ] **Step 1: Probe first (RED).** Extend the `col-drag` step so the cells compared are plot widths (use `axes.w` of the two plots, in logical px) on a row whose first cell is the left one, in addition to the existing checks (+80 px tracking within 1 px, both extremes 96 +/- 1, pair sum preserved). With the old begin code the tracking is off by the gutter; expect `ok=0` before the fix. Keep the other split-probe lines as they are.
+- [ ] **Step 2: Fix** `layout_col_drag_begin` to subtract the gutter from the left cell: `gutter = plot.layout().y_axis_width + plot.layout().y_title_width` of the left plot (0 for a non-first left cell, which has `None`), converted by the same `scale`. Update the comment above `layout_col_apply` to say "plot width".
+- [ ] **Step 3: Verify.** Build; run the split probe; expect `col-drag ok=1` and the previous steps unchanged; layout probe unchanged; `gtk warnings: 0`.
+- [ ] **Step 4: Commit** `git add src/ui.cpp src/ui_probe.cpp src/ui_app.hpp && git commit -m "layout editor: column drag measures plot widths, not cell rects"`.
+
+---
+
+### Task 5: Docs
+
+**Files:** `README.md`, `docs/USER-GUIDE.md`, `help/C/org.udpscope.app/layout.page`, `docs/claude/probe-readings.md`, `docs/claude/verification.md` (new probe line), `docs/claude/invariants-plot-and-layout.md`, `docs/claude/build-and-run.md`, `docs/claude/architecture.md` if it describes per-cell y, `CLAUDE.md` if it mentions per-cell y, `src/ui_context_help.cpp`, `src/ui_tour.cpp` if they say cells have their own y axis.
+
+- [ ] **Step 1:** `grep -rn -i "per cell\|own y\|each cell\|y axis" README.md docs help src/ui_context_help.cpp src/ui_tour.cpp CLAUDE.md` to find every statement that the cells of a split row have their own y axis or one common gutter "not per column"; rewrite each to the new rule: one y range and one y axis per figure row, labels on the left cell, y zoom/pan/fit/Auto-Fixed act on the whole row, one ruler pair per row, cells share the y gutter's width only through the first cell.
+- [ ] **Step 2:** `build-and-run.md`: add the plotter change (`set_share_row_y`, y link semantics, `YStrip`, plot-width cell placement) beside the other vendored changes. `invariants-plot-and-layout.md`: replace the "one gutter, not a per-column one" wording with the structural rule (first cell only, a `None` cell contributes 0, never content-dependent). `probe-readings.md` / `verification.md`: document the `[split-probe] shared-y` line and the changed `ruler-labels` / `col-drag` readings with the defect each wrong value names.
+- [ ] **Step 3:** Build (help/manual and context help compile), run the split probe once more for `gtk warnings: 0`.
+- [ ] **Step 4: Commit** `git add <the files changed> && git commit -m "docs: split rows share one y axis"`.

docs/superpowers/plans/2026-11-03-ui-badges-signals.md

@@ -0,0 +1,832 @@
+# Signal badges -- step 2 of the badge-bar redesign Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Put the signals on the badge bar: one badge per enabled signal (a colour dot and the name; up to 6, then one "N signals" badge), each opening a per-signal slide-over page, each a drag handle (to a plot row, or to reorder), plus a trailing `+` that opens the full signal list as a slide-over page. The signal list leaves the dock.
+
+**Architecture:** The existing `signal_panel` (heading, hint, list, math divider) is *reparented* from the temporary dock into the `signals` slide-over page. A new unit, `src/ui_signal_page.cpp`, owns the lazily-created `signal:<name>` pages (colour, calibration, information, "plot on row N", math edit/delete) and keeps them in step with the model. `src/ui_badges.cpp` grows the signal badges (inside a scroller so the bar's minimum width never depends on how many there are). The drop that today puts a dragged list row on a plot becomes `assign_signal_to_row()`, shared by the drop and by the page's buttons; the badge replaces the list row as the drag source.
+
+**Tech Stack:** C++20, GTK4, libadwaita >= 1.8, CMake. No unit-test suite: verification is the app's own headless self-check (`xvfb-run`, mock sources) -- extend `src/ui_probe.cpp` / `src/ui_badges.cpp` probes, never a separate harness.
+
+Spec: `docs/superpowers/specs/2026-11-02-ui-badges-dock-design.md` ("Badge bar", "Slide-over panel", rollout step 2). Step 1 plan: `docs/superpowers/plans/2026-11-02-ui-badges-dock-shell.md`. Branch: `feature/ui-badges-dock` (continue on it).
+
+## Global Constraints
+
+Copied from the spec and the repository's rules; every task includes them.
+
+- **Layout must not depend on content** (`docs/claude/invariants-plot-and-layout.md`): the badge bar keeps its fixed 36 px height and its minimum width must not grow with the number of signals (the signal badges sit in a `GtkScrolledWindow`, `GTK_POLICY_EXTERNAL` / `GTK_POLICY_NEVER`); the slide-over still overlays and never resizes the plot.
+- **A `GtkOverlay` child is picked wherever its allocation is**: nothing in this step adds an overlay child.
+- Signal badges: "one badge per enabled signal, up to 6; beyond that a single 'N signals' badge. A badge shows a colour dot and the name, is a drag handle (reorder, or drop on a plot row, which replaces today's drag from the signal list), and opens that signal's page (colour, calibration, row, math). A trailing `+` opens the `signals` page (the full list, to enable more; the math editor entry)." (spec, verbatim)
+- Page ids: `trigger`, `signal:<name>`, `signals`, `measure`, `cursors`, `events`, `source-<id>`. This step adds `signals` and `signal:<name>`.
+- One slide-over page at a time; Esc or a click outside closes it; each page has its own scroller; the open page is not saved.
+- "Disable, do not hide": a control that does not apply is insensitive and stays on screen (the one precedent kept is the acquire tick, hidden in a file view -- see `rebuild_signal_list`).
+- Text buttons only for new controls (the `+` is the character, not an icon); no icons in badges. The colour dot is the existing `chip_markup()` disc.
+- The widget-lifetime trap (`docs/claude/invariants-gtk-and-chrome.md`): a click handler that calls `rebuild_signal_panels()` destroys the page/row that owns the emitting button; hold the emitter with `outlive_the_rebuild(widget)` first. A drop handler never destroys the widgets it was emitted from.
+- Every new source file carries the SPDX MIT header (`// SPDX-License-Identifier: MIT` / `// SPDX-FileCopyrightText: 2026 Martino Ferrari`).
+- Baselines: a clean build emits exactly **one** warning (the icons' `-Woverlength-strings`), an incremental build **zero**; the dump's `gtk warnings:` reads `0`; no `Gtk-CRITICAL`/`Gtk-WARNING`.
+- Verification runs are short and serial; kill every mock you start; do not re-run to chase cosmetics. Headless needs `GDK_BACKEND=x11` and, for screenshots, `GSK_RENDERER=cairo` + `import -window root`.
+- Do not push, merge or amend. Commit per task on `feature/ui-badges-dock`.
+
+## Deliberate step-2 deviations from the spec (state them in the final report)
+
+- **Reorder is in memory only.** The badge order lives in `App::badge_order` for the session; it is not written to the session file (the spec's session section lists only the dock state). A new signal sorts after the ordered ones, in model order.
+- **Beyond 6 enabled signals the "N signals" badge replaces the per-signal badges *and* the `+`** (it opens the same `signals` page, so a second button for it would be a duplicate). Per-signal pages for those signals are reached by activating a row of the `signals` list (new in this step); drag-to-row for them is by the page's "Plot on" buttons.
+- **The list's drag source is removed**, as the spec says ("replaces today's drag from the signal list"); `row_drag_sidebar()` goes with it if nothing else calls it.
+- A signal page opened for a signal that is not acquired shows its acquire tick (so a list row can be activated without first being ticked).
+
+## File Structure
+
+| File | Create/Modify | Responsibility |
+| --- | --- | --- |
+| `src/ui_signal_page.cpp` | Create | The `signal:<name>` pages: ensure/fill/prune, their buttons, the `signal_pages` probe helpers. |
+| `src/ui_badges.cpp` | Modify | Signal badges, the `+` badge, "N signals" overflow, scroller, reorder drop, drag source, `signal_badges_probe`. |
+| `src/ui_signals.cpp` | Modify | `listed_signals()`, `assign_signal_to_row()`, `reset_signal_color()`, row-activated -> page, list drag source removed, header comment fixed. |
+| `src/ui_slideover.cpp` | Modify | `slideover_remove_page()`. |
+| `src/ui_app.hpp` | Modify | `Badge` fields, `BadgeBar` fields, `App::badge_order` / `App::signal_pages`, declarations. |
+| `src/ui.cpp` | Modify | Signal panel into the `signals` page; `ShowSignals` opens it; probe env var; `row_drag_sidebar` removal. |
+| `src/ui_tour.cpp`, `src/ui_context_help.cpp` | Modify | The signals step / hint re-pointed to the page; badge text. |
+| `src/ui_probe.cpp` | Modify | Every probe that measured or walked `signal_panel` / `signal_list` while it lived in the dock. |
+| `src/ui_widgets.cpp` | Modify | CSS for the signal badge dot/name if needed. |
+| `CMakeLists.txt` | Modify | Add `src/ui_signal_page.cpp` next to `src/ui_badges.cpp`. |
+| `README.md`, `docs/claude/*.md` | Modify | Task 5. (`USER-GUIDE.md` and the Mallard manual are spec step 4.) |
+
+---
+
+### Task 1: The `signals` page and the `+` badge
+
+The list moves out of the dock into a slide-over page; the `+` badge and the `g` key open it. Nothing else changes yet (the list rows keep their menu and their drag source).
+
+**Files:**
+- Modify: `src/ui.cpp`, `src/ui_badges.cpp`, `src/ui_app.hpp`, `src/ui_signals.cpp` (header comment), `src/ui_tour.cpp`, `src/ui_context_help.cpp`, `src/ui_probe.cpp`
+
+**Interfaces:**
+- Consumes (step 1): `slideover_add_page(App&, const std::string& id, const std::string& title, GtkWidget* content) -> bool`, `slideover_open/close/toggle(App&, ...)`, `slideover_page(const App&) -> std::string`, `Badge{button,name,state,page}`, `make_badge(...)`, `BadgeBar{bar,signals_slot,system_slot,trigger,source}`.
+- Produces: `BadgeBar::plus` (`Badge`, page `"signals"`, name label `"+"`); the `signals` page registered once in `on_activate`.
+
+- [ ] **Step 1: Freeze today's self-check**
+
+Build `HEAD` (`cmake --build build -j`), then:
+
+```sh
+python3 tools/mock_udpstreamer.py --port 8114 --rate 10000 --batch 100 --duration 30 & MOCK=$!
+sleep 1.5
+xvfb-run -a env GDK_BACKEND=x11 UDPSCOPE_EXIT_AFTER_MS=8000 UDPSCOPE_ENABLE_ALL_MS=1000 \
+  ./build/udpscope --server 127.0.0.1 --port 8114 > /tmp/ui-signals-base.log 2>&1
+kill $MOCK
+sed 's/[0-9.]\+/N/g' /tmp/ui-signals-base.log > .superpowers/sdd/ui-signals-baseline-udps.txt
+grep -c 'Gtk-CRITICAL' /tmp/ui-signals-base.log; grep 'gtk warnings' /tmp/ui-signals-base.log
+```
+Expected: `0` and `gtk warnings: 0`. Every later task diffs its own normalised run against this file and must explain every differing line from that task's "allowed baseline changes"; any other difference is a defect.
+
+- [ ] **Step 2: Fix the stray `\n` in `src/ui_signals.cpp` line 4**
+
+The header comment reads `...with its colour chip and acquire tick, the panel around it,\n// and the drop that puts a signal on a row.` on one line (a literal backslash-n). Replace it with two comment lines:
+
+```cpp
+// The signal list: one row per signal with its colour chip and acquire tick, the panel around it,
+// and the drop that puts a signal on a row.
+```
+
+- [ ] **Step 3: Reparent the panel into a `signals` page (`src/ui.cpp`, `on_activate`, ~line 5172)**
+
+Replace
+
+```cpp
+  app->signal_panel = build_signal_panel(*app);
+  gtk_box_append(GTK_BOX(app->dock_page), app->signal_panel);
+  gtk_box_append(GTK_BOX(app->dock_page), gtk_separator_new(GTK_ORIENTATION_HORIZONTAL));
+  gtk_box_append(GTK_BOX(app->dock_page), app->cursors_panel);
+```
+with
+```cpp
+  app->signal_panel = build_signal_panel(*app);
+  gtk_box_append(GTK_BOX(app->dock_page), app->cursors_panel);
+```
+and register the page where the other pages are registered (after `build_slideover`, next to the `"trigger"` page; the panel must exist first, so if that registration happens before line 5172, add the `slideover_add_page(*app, "signals", "Signals", app->signal_panel);` call right after the panel is built instead):
+
+```cpp
+  slideover_add_page(*app, "signals", "Signals", app->signal_panel);
+```
+Read the surrounding code before editing: the registration must happen once, after `build_slideover(*app)` and after `build_signal_panel`. Update the comments that say the dock holds "the signal list, the cursors and the measurements" (`dock_show_section`, `ui_app.hpp` `dock_page`) to "the cursors and the measurements".
+
+- [ ] **Step 4: `g` opens the page (`run_app_action`, ~line 4682)**
+
+```cpp
+    case AppAction::ShowSignals: slideover_toggle(app, "signals"); break;
+```
+and in `dock_show_section` delete the `"signals"` branch (the dock no longer holds the list); keep `"measure"`.
+
+- [ ] **Step 5: The `+` badge (`src/ui_badges.cpp`, `src/ui_app.hpp`)**
+
+In `BadgeBar` add `Badge plus;`. In `build_badge_bar`, after the Source badge:
+
+```cpp
+  // The full signal list. Insensitive until the stream has declared signals ("disable, do not hide").
+  make_badge(app, bb.plus, bb.signals_slot, "+", "signals");
+  gtk_widget_set_tooltip_text(bb.plus.button, "all signals: switch more on, add a math channel");
+```
+(`make_badge` appends a second, empty `state` label; for `+` leave it empty, it takes no width.) In `sync_badge_bar`, before the early return at the `bb.source.button == nullptr` check:
+
+```cpp
+  if (bb.plus.button != nullptr) {
+    gtk_widget_set_sensitive(bb.plus.button, !app.model->signals().empty());
+    set_open(bb.plus.button, slideover_page(app) == "signals");
+  }
+```
+Step 2's later tasks insert the signal badges *before* the `+` in `signals_slot`; Task 3 handles the ordering, so do not worry about it here.
+
+- [ ] **Step 6: Tour and context help**
+
+`src/ui_tour.cpp`: the `"signals"` step (line ~460) becomes `{"signals", "signals", "The signals", ...}` (second field is the slide-over page; see the `"trigger"` step), text: `"Every signal the source declares, each with the switch that acquires it. The + badge opens this list; a signal has to be switched on before it can be plotted, measured or searched."`. The `"side"` step text becomes `"The dock beside the plot: the cursors, then the measurements. The buttons in the bar above show and hide it."`. Keep `&App::signal_list` as the rect. `src/ui_context_help.cpp` line ~92: replace the last sentence of the `"signals"` hint (`A signal that is dragged onto a plot is drawn there.`) with `A signal's badge, dragged onto a plot, draws it there.`; the `"signals_config"` hint's `which plot a signal is dragged onto` becomes `which plot a signal is drawn on`.
+
+- [ ] **Step 7: Re-point the probes that treated the list as part of the dock**
+
+`src/ui_probe.cpp` references `signal_panel`/`signal_list` at ~103-186, ~1828, ~1853, ~3843-3847, ~5827, ~6165, ~6431 and the tour-surface probe ~7024-7097. The page is closed by default, so widgets inside it are unmapped and have no allocation. For each: (a) a probe that measures the panel's allocated size -- open the `signals` page first (`slideover_open(*a, "signals")`) and close it after, or measure with `gtk_widget_measure`; (b) a probe that walks the rows needs nothing (children exist while unmapped); (c) the stress line at ~1853 (`gtk_widget_set_size_request(a->signal_panel, -1, 3000)`) existed to overflow the *dock's* scroller; re-point it to `a->cursors_panel`; (d) the `ShowSignals` check at ~6431 asserts `slideover_page(*a) == "signals"` and then closes it; (e) `~6165` (`gtk_widget_get_parent(app.signal_list)`) -- read what it needs and take it from the page instead. Print the same lines as before wherever the value is still meaningful.
+
+- [ ] **Step 8: Verify**
+
+```sh
+cmake --build build -j 2>&1 | grep -E 'warning|error'; echo "rc=$?"
+python3 tools/mock_udpstreamer.py --port 8114 --rate 10000 --batch 100 --duration 30 & MOCK=$!
+sleep 1.5
+xvfb-run -a env GDK_BACKEND=x11 UDPSCOPE_EXIT_AFTER_MS=8000 UDPSCOPE_ENABLE_ALL_MS=1000 \
+  ./build/udpscope --server 127.0.0.1 --port 8114 > /tmp/ui-signals-t1.log 2>&1
+kill $MOCK
+sed 's/[0-9.]\+/N/g' /tmp/ui-signals-t1.log | diff .superpowers/sdd/ui-signals-baseline-udps.txt - ; grep -c Gtk-CRITICAL /tmp/ui-signals-t1.log; grep 'gtk warnings' /tmp/ui-signals-t1.log
+```
+Then run `UDPSCOPE_PROBE_SLIDEOVER_MS=1500`, `UDPSCOPE_PROBE_BADGES_MS=1500` and `UDPSCOPE_PROBE_TOUR_SURFACE_MS=<as in verification.md>` the same way. Expected: zero build warnings; the slide-over and badge probes read as in step 1 (`table_bad=0`, `open_marked=1`, `closed_unmarked=1`); the tour-surface probe shows the `signals` step now opens the `signals` page and `tour_plan_holds(signal_list)=1`. **Allowed baseline changes:** the dock's size/position lines that included the list (re-pointed per Step 7), any `signal_panel` geometry line. Explain each in the report.
+
+- [ ] **Step 9: Commit**
+
+```sh
+git add -A src docs
+git commit -m "ui: the signal list is the signals slide-over page, opened by a + badge or g"
+```
+
+---
+
+### Task 2: Per-signal pages, `assign_signal_to_row()` and `reset_signal_color()`
+
+Builds `signal:<name>` pages (nothing opens them yet except activating a list row) and extracts the two actions the page shares with the list.
+
+**Files:**
+- Create: `src/ui_signal_page.cpp`
+- Modify: `src/ui_signals.cpp`, `src/ui_slideover.cpp`, `src/ui_app.hpp`, `src/ui.cpp` (probe env var), `src/ui_probe.cpp` or `src/ui_signal_page.cpp` (probe), `CMakeLists.txt`
+
+**Interfaces:**
+- Produces (declare in `ui_app.hpp`, namespace `udpscope::ui_impl`):
+
+```cpp
+/// Every plottable signal once (the time base skipped, a group's layers folded to the first), in model order.
+/// The one rule the list and the badges share.
+std::vector<std::size_t> listed_signals(const std::vector<SignalInfo>& signals);
+/// Puts `signal` (an index into `signals()`) on plot `row` in the first free slot, switching it on first if
+/// need be. Says why not through `set_notice` and returns false when it cannot. The one path a drop and a
+/// signal page's "Plot on" button share.
+bool assign_signal_to_row(App& app, std::size_t signal, int row);
+/// Back to the palette colour for the signal's position.
+void reset_signal_color(App& app, std::size_t signal);
+/// Holds `widget` alive across the current emission (was `static` in ui_signals.cpp).
+void outlive_the_rebuild(GtkWidget* widget);
+bool slideover_remove_page(App& app, const std::string& id);   // ui_slideover.cpp
+/// Creates the page `signal:<name>` if it is missing, fills it, and returns whether it exists afterwards.
+bool signal_page_ensure(App& app, const std::string& name);
+/// Called at the end of `rebuild_signal_panels`: refills every existing signal page, drops the pages of
+/// signals the model no longer has (closing the slide-over first if one of them is open).
+void signal_pages_sync(App& app);
+```
+- `App` gains `std::map<std::string, GtkWidget*> signal_pages;` (name -> the page's content box).
+
+- [ ] **Step 1: `listed_signals()`**
+
+In `src/ui_signals.cpp`, add (before `rebuild_signal_list`):
+
+```cpp
+std::vector<std::size_t> listed_signals(const std::vector<SignalInfo>& signals) {
+  std::vector<std::size_t> out;
+  for (std::size_t i = 0; i < signals.size(); ++i) {
+    if (ScopeModel::is_time_signal(signals, i)) continue;  // the time base is not plottable
+    const std::string base = layer_base_name(signals[i].name);
+    bool seen = false;
+    for (std::size_t j = 0; j < i && !seen; ++j) {
+      seen = !ScopeModel::is_time_signal(signals, j) && layer_base_name(signals[j].name) == base;
+    }
+    if (!seen) out.push_back(i);
+  }
+  return out;
+}
+```
+and make `rebuild_signal_list` use it:
+
+```cpp
+  std::vector<std::size_t> rows;
+  for (std::size_t i : listed_signals(signals)) {
+    // Locked: a row per signal that is *on* ... (keep the existing comment)
+    if (app.signals_locked && !app.model->signal_enabled(i)) continue;
+    rows.push_back(i);
+  }
+```
+Behaviour is unchanged (the dump's `rows == signals + 1 + math` line must not move).
+
+- [ ] **Step 2: `assign_signal_to_row()`**
+
+Move lines `on_drop_channel` from `if (signal >= app->model->signals().size()) return FALSE;` through `notice("plotting '" ...)` into the new function, with `app->` -> `app.`; keep the `notice` lambda, the "enable it, then take the channel that appears" branch, the free-slot search and the two refusal messages verbatim, `return false`/`return true`. `on_drop_channel` becomes:
+
+```cpp
+gboolean on_drop_channel(GtkDropTarget*, const GValue* value, double x, double y, gpointer user) {
+  App* app = static_cast<App*>(user);
+  if (!G_VALUE_HOLDS_STRING(value)) return FALSE;
+  const int row = row_at(*app, x, y);  // where the drop landed decides the row: one area covers them all
+  const char* text = g_value_get_string(value);
+  const std::size_t signal = static_cast<std::size_t>(std::atoll(text ? text : "0"));
+  if (!assign_signal_to_row(*app, signal, row)) return FALSE;
+  cancel_drag_on(*app, row);
+  return TRUE;
+}
+```
+`rebuild_signal_panels(app)` stays inside `assign_signal_to_row` (before the notice), as it is today.
+
+- [ ] **Step 3: `reset_signal_color()`**
+
+Extract the body of the `recolor` lambda (`ui_signals.cpp` ~386-401) into:
+
+```cpp
+void reset_signal_color(App& app, std::size_t signal) {
+  std::string name;
+  {
+    std::lock_guard<std::mutex> lock(app.model->mutex());
+    const std::vector<SignalInfo>& sigs = app.model->signals();
+    if (signal >= sigs.size()) return;
+    name = sigs[signal].name;
+  }
+  app.rows->clear_signal_color(name);
+  app.relayout_pending = true;
+  rebuild_signal_panels(app);
+  schedule_layout_save(app);
+}
+```
+The lambda keeps `outlive_the_rebuild(GTK_WIDGET(b))` first (the list rebuild destroys it) and then calls this. Remove `static` from `outlive_the_rebuild` and move its definition above `rebuild_signal_list` users unchanged.
+
+- [ ] **Step 4: `slideover_remove_page()` (`src/ui_slideover.cpp`)**
+
+Read how `slideover_add_page` records a page (stack child name, any title/page registry on `SlideOver`). Implement the inverse: returns false if the id is unknown; refuses (returns false) if it is the open page; otherwise removes the stack child (`gtk_stack_remove`) and erases whatever registry entry `slideover_add_page` made.
+
+- [ ] **Step 5: `src/ui_signal_page.cpp`**
+
+Create the file with the SPDX header, `#include "ui_app.hpp"`, `<gtk/gtk.h>`, `<string>`, namespaces `udpscope::ui_impl`. Page ids are `"signal:" + name`. Contents (an anonymous namespace plus the two public functions):
+
+```cpp
+namespace {
+
+std::string page_id(const std::string& name) { return "signal:" + name; }
+
+/// The index of `name` in the model's signals, or npos.
+std::size_t signal_index(App& app, const std::string& name) {
+  std::lock_guard<std::mutex> lock(app.model->mutex());
+  const std::vector<SignalInfo>& s = app.model->signals();
+  for (std::size_t i = 0; i < s.size(); ++i) {
+    if (s[i].name == name) return i;
+  }
+  return std::string::npos;
+}
+
+GtkWidget* text_button(const char* label, GtkWidget* parent) {
+  GtkWidget* b = gtk_button_new_with_label(label);
+  gtk_box_append(GTK_BOX(parent), b);
+  return b;
+}
+
+/// Stores the signal's index and the page's name on the button, so a handler resolves identity the way the
+/// list does.
+void tag(GtkWidget* b, std::size_t index) {
+  g_object_set_data(G_OBJECT(b), "udpscope-signal", GSIZE_TO_POINTER(index));
+}
+std::size_t tagged(GtkButton* b) {
+  return static_cast<std::size_t>(GPOINTER_TO_SIZE(g_object_get_data(G_OBJECT(b), "udpscope-signal")));
+}
+
+void fill(App& app, const std::string& name, GtkWidget* page) {
+  for (GtkWidget* c = gtk_widget_get_first_child(page); c != nullptr;) {
+    GtkWidget* next = gtk_widget_get_next_sibling(c);
+    gtk_box_remove(GTK_BOX(page), c);
+    c = next;
+  }
+  const std::size_t index = signal_index(app, name);
+  if (index == std::string::npos) return;
+  // A snapshot, taken under the lock: the chip helper wants the whole vector, and the producer replaces it
+  // on every CONFIG.
+  std::vector<SignalInfo> all;
+  {
+    std::lock_guard<std::mutex> lock(app.model->mutex());
+    all = app.model->signals();
+  }
+  if (index >= all.size()) return;
+  const SignalInfo sig = all[index];
+  const bool enabled = app.model->signal_enabled(index);
+  const bool plotted = signal_plotted(app, sig.name);
+  const bool unlocked = !app.signals_locked;
+
+  // Back to the list: a page reached from a list row has no other way home.
+  GtkWidget* back = text_button("All signals", page);
+  gtk_widget_set_halign(back, GTK_ALIGN_START);
+  gtk_widget_add_css_class(back, "flat");
+  g_signal_connect(back, "clicked", G_CALLBACK(+[](GtkButton*, gpointer user) {
+                     slideover_open(*static_cast<App*>(user), "signals");
+                   }),
+                   &app);
+
+  GtkWidget* title = gtk_label_new(sig.name.c_str());
+  gtk_widget_add_css_class(title, "title-3");
+  gtk_widget_set_halign(title, GTK_ALIGN_START);
+  gtk_label_set_ellipsize(GTK_LABEL(title), PANGO_ELLIPSIZE_END);
+  gtk_box_append(GTK_BOX(page), title);
+  if (!sig.unit.empty()) {
+    GtkWidget* unit = gtk_label_new(sig.unit.c_str());
+    gtk_widget_add_css_class(unit, "dim-label");
+    gtk_widget_set_halign(unit, GTK_ALIGN_START);
+    gtk_box_append(GTK_BOX(page), unit);
+  }
+
+  // Acquire / compute. The same handler as the list's tick, which reads the signal index off the widget.
+  GtkWidget* enable = gtk_check_button_new_with_label(sig.math ? "Compute this channel" : "Acquire this signal");
+  app.updating_panels = true;
+  gtk_check_button_set_active(GTK_CHECK_BUTTON(enable), enabled);
+  app.updating_panels = false;
+  g_object_set_data(G_OBJECT(enable), "udpscope-signal", GSIZE_TO_POINTER(index));
+  g_signal_connect(enable, "notify::active", G_CALLBACK(on_signal_switch), &app);
+  gtk_widget_set_visible(enable, sig.math || app.waveform_name.empty());
+  gtk_box_append(GTK_BOX(page), enable);
+
+  // Colour.
+  GtkWidget* colour_head = gtk_label_new("Colour");
+  gtk_widget_add_css_class(colour_head, "heading");
+  gtk_widget_set_halign(colour_head, GTK_ALIGN_START);
+  gtk_box_append(GTK_BOX(page), colour_head);
+  GtkWidget* chip = gtk_label_new(nullptr);
+  gtk_label_set_markup(GTK_LABEL(chip), signal_chip_markup(app, all, index).c_str());
+  GtkWidget* colour_row = gtk_box_new(GTK_ORIENTATION_HORIZONTAL, 8);
+  gtk_box_append(GTK_BOX(colour_row), chip);
+  GtkWidget* pick = text_button("Change colour...", colour_row);
+  gtk_widget_set_sensitive(pick, plotted && unlocked);
+  gtk_widget_set_tooltip_text(pick, plotted ? "the colour this signal is plotted in"
+                                            : "on no plot, so there is no trace to colour");
+  tag(pick, index);
+  g_signal_connect(pick, "clicked", G_CALLBACK(+[](GtkButton* b, gpointer user) {
+                     open_signal_color(*static_cast<App*>(user), tagged(b));
+                   }),
+                   &app);
+  GtkWidget* reset = text_button("Default colour", colour_row);
+  gtk_widget_set_sensitive(reset, unlocked && app.rows->signal_colors().count(sig.name) != 0);
+  tag(reset, index);
+  g_signal_connect(reset, "clicked", G_CALLBACK(+[](GtkButton* b, gpointer user) {
+                     outlive_the_rebuild(GTK_WIDGET(b));
+                     reset_signal_color(*static_cast<App*>(user), tagged(b));
+                   }),
+                   &app);
+  gtk_box_append(GTK_BOX(page), colour_row);
+
+  // Row: "Plot on 1 2 3 ..." and the way back off.
+  GtkWidget* row_head = gtk_label_new("Plot on");
+  gtk_widget_add_css_class(row_head, "heading");
+  gtk_widget_set_halign(row_head, GTK_ALIGN_START);
+  gtk_box_append(GTK_BOX(page), row_head);
+  GtkWidget* rows_box = gtk_box_new(GTK_ORIENTATION_HORIZONTAL, 4);
+  for (int r = 0; r < app.rows->row_count(); ++r) {
+    GtkWidget* b = text_button(std::to_string(r + 1).c_str(), rows_box);
+    tag(b, index);
+    g_object_set_data(G_OBJECT(b), "udpscope-row", GINT_TO_POINTER(r));
+    gtk_widget_set_tooltip_text(b, "draw this signal on this plot");
+    g_signal_connect(b, "clicked", G_CALLBACK(+[](GtkButton* b, gpointer user) {
+                       outlive_the_rebuild(GTK_WIDGET(b));
+                       assign_signal_to_row(*static_cast<App*>(user), tagged(b),
+                                            GPOINTER_TO_INT(g_object_get_data(G_OBJECT(b), "udpscope-row")));
+                     }),
+                     &app);
+  }
+  gtk_box_append(GTK_BOX(page), rows_box);
+  GtkWidget* off = text_button("Remove from plots", page);
+  gtk_widget_set_halign(off, GTK_ALIGN_START);
+  gtk_widget_set_sensitive(off, plotted);
+  tag(off, index);
+  g_signal_connect(off, "clicked", G_CALLBACK(+[](GtkButton* b, gpointer user) {
+                     App* a = static_cast<App*>(user);
+                     outlive_the_rebuild(GTK_WIDGET(b));
+                     std::string n;
+                     {
+                       std::lock_guard<std::mutex> lock(a->model->mutex());
+                       const std::vector<SignalInfo>& s = a->model->signals();
+                       if (tagged(b) >= s.size()) return;
+                       n = s[tagged(b)].name;
+                     }
+                     const int gone = remove_signal_from_plots(*a, n);
+                     a->relayout_pending = true;
+                     rebuild_signal_panels(*a);
+                     schedule_layout_save(*a);
+                     set_notice(*a, "'" + n + "' left " + std::to_string(gone) + (gone == 1 ? " plot" : " plots"), 4);
+                   }),
+                   &app);
+
+  // Information (a streamed signal's), calibration (ditto), and a math channel's editor.
+  GtkWidget* more_head = gtk_label_new(sig.math ? "Math channel" : "Signal");
+  gtk_widget_add_css_class(more_head, "heading");
+  gtk_widget_set_halign(more_head, GTK_ALIGN_START);
+  gtk_box_append(GTK_BOX(page), more_head);
+  GtkWidget* more = gtk_box_new(GTK_ORIENTATION_HORIZONTAL, 6);
+  if (sig.math) {
+    GtkWidget* edit = text_button("Edit graph...", more);
+    tag(edit, index);
+    g_signal_connect(edit, "clicked", G_CALLBACK(on_math_edit_clicked), &app);
+    GtkWidget* del = text_button("Delete", more);
+    gtk_widget_add_css_class(del, "destructive-action");
+    tag(del, index);
+    g_signal_connect(del, "clicked", G_CALLBACK(on_math_delete_clicked), &app);
+  } else {
+    GtkWidget* info = text_button("Information", more);
+    tag(info, index);
+    g_signal_connect(info, "clicked", G_CALLBACK(on_info_clicked), &app);
+    GtkWidget* cal = text_button("Calibrate...", more);
+    gtk_widget_set_sensitive(cal, unlocked);
+    gtk_widget_set_tooltip_text(cal, "gain and offset, applied at ingest");
+    tag(cal, index);
+    g_signal_connect(cal, "clicked", G_CALLBACK(+[](GtkButton* b, gpointer user) {
+                       App* a = static_cast<App*>(user);
+                       open_calibration(*a, GTK_WINDOW(a->window), tagged(b));
+                     }),
+                     &app);
+  }
+  gtk_box_append(GTK_BOX(page), more);
+}
+
+}  // namespace
+```
+`on_math_edit_clicked`, `on_math_delete_clicked`, `on_info_clicked`, `open_calibration`, `open_signal_color`, `signal_plotted` and `signal_chip_markup` are already declared in `ui_app.hpp` (check; if `on_math_edit_clicked` / `on_math_delete_clicked` are not, add the declarations). `on_math_edit_clicked` calls `dismiss_row_menu(button)`, which looks for a `GtkPopover` ancestor and does nothing when there is none -- confirm that by reading it. `on_math_delete_clicked` already calls `outlive_the_rebuild`. Then the two public functions:
+
+```cpp
+bool signal_page_ensure(App& app, const std::string& name) {
+  if (signal_index(app, name) == std::string::npos) return false;
+  auto it = app.signal_pages.find(name);
+  if (it == app.signal_pages.end()) {
+    GtkWidget* page = gtk_box_new(GTK_ORIENTATION_VERTICAL, 8);
+    gtk_widget_set_margin_top(page, 12);
+    gtk_widget_set_margin_bottom(page, 12);
+    gtk_widget_set_margin_start(page, 12);
+    gtk_widget_set_margin_end(page, 12);
+    if (!slideover_add_page(app, page_id(name), name, page)) return false;
+    it = app.signal_pages.emplace(name, page).first;
+  }
+  fill(app, name, it->second);
+  return true;
+}
+
+void signal_pages_sync(App& app) {
+  for (auto it = app.signal_pages.begin(); it != app.signal_pages.end();) {
+    if (signal_index(app, it->first) == std::string::npos) {
+      if (slideover_page(app) == page_id(it->first)) slideover_close(app);
+      slideover_remove_page(app, page_id(it->first));
+      it = app.signal_pages.erase(it);
+    } else {
+      fill(app, it->first, it->second);
+      ++it;
+    }
+  }
+}
+```
+`slideover_add_page` wraps `content` in a scroller and returns it through the stack, so `page` stays the box `fill` clears. Check that the gtk widget `page` is not destroyed by `slideover_remove_page` before `erase` (it is not used afterwards). Call `signal_pages_sync(app)` at the end of `rebuild_signal_panels` (before `app.signal_generation = ...`). `signal_index` takes the model mutex, so `signal_pages_sync` must not be called with it held (`rebuild_signal_panels` releases it before the list rebuild).
+
+- [ ] **Step 6: A list row opens its page**
+
+In `rebuild_signal_list`, tag each row: `g_object_set_data(G_OBJECT(row), "udpscope-signal", GSIZE_TO_POINTER(i));` (the math divider row has none and is not activatable). In `build_signal_panel`, after the null check:
+
+```cpp
+  g_signal_connect(app.signal_list, "row-activated",
+                   G_CALLBACK(+[](GtkListBox*, GtkListBoxRow* row, gpointer user) {
+                     App* a = static_cast<App*>(user);
+                     const std::size_t index = static_cast<std::size_t>(
+                         GPOINTER_TO_SIZE(g_object_get_data(G_OBJECT(row), "udpscope-signal")));
+                     std::string name;
+                     {
+                       std::lock_guard<std::mutex> lock(a->model->mutex());
+                       const std::vector<SignalInfo>& s = a->model->signals();
+                       if (index >= s.size()) return;
+                       name = s[index].name;
+                     }
+                     if (signal_page_ensure(*a, name)) slideover_open(*a, "signal:" + name);
+                   }),
+                   &app);
+```
+If `signals-panel.ui`'s list box has `activate-on-single-click` off or selection mode that swallows activation, set `activate-on-single-click` to true in code. Read the file; the row's own check button / colour-chip gesture / menu button must still work (they consume their own clicks).
+
+- [ ] **Step 7: Probe `UDPSCOPE_PROBE_SIGNAL_PAGES_MS`**
+
+Declare `gboolean signal_page_probe(gpointer)` (put it in `ui_signal_page.cpp`), schedule it in `ui.cpp` next to the badges probe. It takes the first non-math listed signal (from `listed_signals`), calls `signal_page_ensure`, `slideover_open("signal:<name>")` and prints:
+
+```
+[signalpage] name=<n> open=<slideover_page==id> pages=<signal_pages.size()> enable_visible=<0|1> plot_buttons=<count of the "Plot on" buttons> plot_on_row0=<1 if assign_signal_to_row(...,0) returned true and signal_plotted> removed=<remove button click leaves signal_plotted false> back_to_list=<slideover_open("signals") -> page "signals"> pruned=<1 after the page's signal is gone>
+```
+To check `pruned` without a CONFIG, call `slideover_close`, `slideover_remove_page` directly is *not* a test of `signal_pages_sync`; instead leave `pruned=-1` when it cannot be exercised, and exercise `signal_pages_sync` by the ordinary reconfiguration paths (adding then deleting a math channel with `add_math_channel` / `a->math.erase(...)`+`apply_math_channels` if the probe harness already does that elsewhere; otherwise `-1`). Close the slide-over at the end.
+
+- [ ] **Step 8: Verify**
+
+Build (zero warnings), then the UDPS baseline run as in Task 1 Step 8 diffed against `.superpowers/sdd/ui-signals-baseline-udps.txt` (expected: the Task 1 differences only), then:
+
+```sh
+python3 tools/mock_udpstreamer.py --port 8114 --rate 10000 --batch 100 --duration 30 & MOCK=$!
+sleep 1.5
+xvfb-run -a env GDK_BACKEND=x11 UDPSCOPE_EXIT_AFTER_MS=5000 UDPSCOPE_ENABLE_ALL_MS=500 UDPSCOPE_PROBE_SIGNAL_PAGES_MS=1500 \
+  ./build/udpscope --server 127.0.0.1 --port 8114 2>&1 | grep -E '\[signalpage\]|\[udpscope\] drop|Gtk-|gtk warnings'
+kill $MOCK
+```
+Expected: `open=1 plot_on_row0=1 removed=1 back_to_list=1`, `plot_buttons` equal to the figure's row count, `gtk warnings: 0`, no `Gtk-CRITICAL`. The existing drop probes (`[drop]` lines in the baseline) must read unchanged: they now run through `assign_signal_to_row`.
+
+- [ ] **Step 9: Commit**
+
+```sh
+git add -A src CMakeLists.txt docs
+git commit -m "ui: per-signal slide-over pages; the drop's assignment and the colour reset as shared functions"
+```
+
+---
+
+### Task 3: The signal badges, the "N signals" overflow and the order
+
+**Files:**
+- Modify: `src/ui_badges.cpp`, `src/ui_app.hpp`, `src/ui_signals.cpp` (call), `src/ui.cpp` (probe env var), `src/ui_widgets.cpp` (CSS, if any)
+
+**Interfaces:**
+- Consumes: `listed_signals`, `signal_page_ensure`, `signal_chip_markup`, `signal_pages_sync` (Task 2).
+- Produces:
+
+```cpp
+// ui_app.hpp
+struct Badge { /* existing */ std::string signal_name; std::size_t signal = 0; };   // the two new fields: empty/0 for non-signal badges
+struct BadgeBar {
+  /* existing */
+  GtkWidget* signals_row = nullptr;                     ///< the box inside the scroller: signal badges, then "+"
+  std::vector<std::unique_ptr<Badge>> signal_badges;    ///< one per shown enabled signal; empty when overflowed
+  Badge overflow;                                       ///< the "N signals" badge, used only beyond kMaxSignalBadges
+  Badge plus;                                           ///< (Task 1)
+};
+inline constexpr std::size_t kMaxSignalBadges = 6;
+// App: std::vector<std::string> badge_order;           ///< names, in the order the user left the badges (memory only)
+void sync_signal_badges(App& app);                      ///< rebuilds the signal badges from the model; ui_badges.cpp
+gboolean signal_badges_probe(gpointer user);
+```
+Include `<memory>` in `ui_app.hpp` if it is not already.
+
+- [ ] **Step 1: Put the signals in a scroller (`build_badge_bar`)**
+
+Before creating any badge:
+
+```cpp
+  // The signal badges sit in a scroller: a bar whose minimum width grew with the number of signals would
+  // widen the window (layout must not depend on content). EXTERNAL scrolls by wheel/touch with no bar.
+  GtkWidget* scroller = gtk_scrolled_window_new();
+  gtk_scrolled_window_set_policy(GTK_SCROLLED_WINDOW(scroller), GTK_POLICY_EXTERNAL, GTK_POLICY_NEVER);
+  gtk_widget_set_hexpand(scroller, TRUE);
+  bb.signals_row = gtk_box_new(GTK_ORIENTATION_HORIZONTAL, 6);
+  gtk_scrolled_window_set_child(GTK_SCROLLED_WINDOW(scroller), bb.signals_row);
+  gtk_box_append(GTK_BOX(bb.signals_slot), scroller);
+```
+and change the `+` badge to `make_badge(app, bb.plus, bb.signals_row, "+", "signals")` (it follows the signal badges because they are inserted before it; see Step 3). Move `make_badge`'s parent argument usage accordingly.
+
+- [ ] **Step 2: `make_signal_badge`**
+
+In the anonymous namespace of `ui_badges.cpp`:
+
+```cpp
+/// A signal's badge: its colour dot (grey when it has no trace) and its name. Words and a dot, no icon.
+void make_signal_badge(App& app, Badge& b, const std::vector<SignalInfo>& signals, std::size_t index) {
+  b.signal = index;
+  b.signal_name = signals[index].name;
+  b.page = "signal:" + b.signal_name;
+  b.button = gtk_button_new();
+  gtk_widget_add_css_class(b.button, "flat");
+  gtk_widget_add_css_class(b.button, "udpscope-badge");
+  GtkWidget* row = gtk_box_new(GTK_ORIENTATION_HORIZONTAL, 6);
+  GtkWidget* dot = gtk_label_new(nullptr);
+  gtk_label_set_markup(GTK_LABEL(dot), signal_chip_markup(app, signals, index).c_str());
+  b.name = gtk_label_new(b.signal_name.c_str());
+  gtk_label_set_ellipsize(GTK_LABEL(b.name), PANGO_ELLIPSIZE_END);
+  gtk_label_set_max_width_chars(GTK_LABEL(b.name), 14);
+  gtk_box_append(GTK_BOX(row), dot);
+  gtk_box_append(GTK_BOX(row), b.name);
+  gtk_button_set_child(GTK_BUTTON(b.button), row);
+  gtk_widget_set_tooltip_text(b.button, b.signal_name.c_str());
+  g_object_set_data(G_OBJECT(b.button), "udpscope-app", &app);
+  g_signal_connect(b.button, "clicked", G_CALLBACK(on_badge_clicked), &b);
+}
+```
+`b.state` stays `nullptr`; `sync_badge_bar` never touches it for these. In `on_badge_clicked`, before `slideover_toggle(*app, b->page)`:
+
+```cpp
+  // A signal's page is made on first use (and kept in step by `signal_pages_sync`).
+  if (b->page.rfind("signal:", 0) == 0 && !signal_page_ensure(*app, b->signal_name)) return;
+```
+
+- [ ] **Step 3: `sync_signal_badges`**
+
+```cpp
+void sync_signal_badges(App& app) {
+  BadgeBar& bb = app.badges;
+  if (bb.signals_row == nullptr) return;
+  std::vector<SignalInfo> signals;
+  {
+    std::lock_guard<std::mutex> lock(app.model->mutex());
+    signals = app.model->signals();
+  }
+  // The enabled signals, in the user's order: names in `badge_order` first, the rest in model order.
+  std::vector<std::size_t> shown;
+  for (std::size_t i : listed_signals(signals)) {
+    if (app.model->signal_enabled(i)) shown.push_back(i);
+  }
+  const auto rank = [&](std::size_t i) {
+    const auto it = std::find(app.badge_order.begin(), app.badge_order.end(), signals[i].name);
+    return static_cast<std::size_t>(it - app.badge_order.begin());  // == size() when unknown: sorts last
+  };
+  std::stable_sort(shown.begin(), shown.end(), [&](std::size_t a, std::size_t b) { return rank(a) < rank(b); });
+
+  // Clear: every signal badge, and the overflow if it was there. The "+" is kept.
+  for (GtkWidget* c = gtk_widget_get_first_child(bb.signals_row); c != nullptr;) {
+    GtkWidget* next = gtk_widget_get_next_sibling(c);
+    if (c != bb.plus.button) gtk_box_remove(GTK_BOX(bb.signals_row), c);
+    c = next;
+  }
+  bb.signal_badges.clear();
+  bb.overflow = Badge{};
+
+  const bool overflowed = shown.size() > kMaxSignalBadges;
+  if (overflowed) {
+    make_badge(app, bb.overflow, bb.signals_row, "", "signals");
+    gtk_label_set_text(GTK_LABEL(bb.overflow.name), (std::to_string(shown.size()) + " signals").c_str());
+  } else {
+    for (std::size_t i : shown) {
+      bb.signal_badges.push_back(std::make_unique<Badge>());
+      make_signal_badge(app, *bb.signal_badges.back(), signals, i);
+      gtk_box_insert_child_after(GTK_BOX(bb.signals_row), bb.signal_badges.back()->button,
+                                 gtk_widget_get_prev_sibling(bb.plus.button));
+    }
+  }
+  // The overflow badge stands for the "+" (it opens the same page); the "+" is shown only when it is not.
+  gtk_widget_set_visible(bb.plus.button, !overflowed);
+  sync_badge_bar(app);
+}
+```
+`make_badge` appends to its parent; for the overflow badge it lands after the `+`, which is hidden then, so the order is immaterial. `make_badge(..., "", ...)` with an empty name: fine, the text is set right after. (`Badge{}` assignment: `Badge` holds only pointers/strings so this is a plain reset; the overflow button was destroyed by the clear loop.) The "+" being hidden when overflowed is the one deliberate use of hiding: the overflow badge replaces it. In `sync_badge_bar` add, for each signal badge and the overflow, `set_open(button, slideover_page(app) == badge.page)` (the overflow's page is `"signals"`, so it shares the `+`'s rule: both read the same state, only one is visible).
+
+- [ ] **Step 4: Rebuild when the model's structure or a plot assignment changes**
+
+At the end of `rebuild_signal_panels` (after `signal_pages_sync(app)` from Task 2) add `sync_signal_badges(app);`. Also call it once at the end of `build_badge_bar` (after the `+` is created) so the first frame is right. Also add `std::vector<std::string> badge_order;` and `#include <algorithm>` / `<memory>` where needed. Every event that changes a dot (assign, remove, colour, enable) already calls `rebuild_signal_panels`.
+
+- [ ] **Step 5: Probe `UDPSCOPE_PROBE_SIGNAL_BADGES_MS`**
+
+Schedule `signal_badges_probe` in `ui.cpp` (like the badges probe). It prints one line:
+
+```
+[sigbadges] enabled=<shown count> badges=<signal_badges.size()> overflow=<0|1> overflow_text=<text|-> plus_visible=<0|1> dot_plotted=<number of badges whose dot is not the unplotted grey; compute by signal_plotted> bar_h=<gtk_widget_get_height(bar)> bar_h_fixed=<1 if bar_h before == after toggling one signal off and on> bar_min_w=<gtk_widget_measure min width of badge_bar> opens=<1 if emitting "clicked" on badges[0] makes slideover_page == signal:<name>, and a second emit closes it> plus_opens=<1 if the same for plus (or the overflow when overflowed)>
+```
+Toggle a signal with `app.model->set_signal_enabled(i, false)` then `rebuild_signal_panels(app)`, and back. `bar_min_w` is only a record: the check is that it is the same with the mock's N signals as `bar_min_w` printed by the E-1608 run in Task 5 (stated there).
+
+- [ ] **Step 6: Verify**
+
+Build (zero warnings). UDPS run with `UDPSCOPE_ENABLE_ALL_MS=500 UDPSCOPE_PROBE_SIGNAL_BADGES_MS=1500` against the mock: expected `badges == enabled` (or `overflow=1` if the mock declares more than 6), `bar_h=36` or the bar's measured value with `bar_h_fixed=1`, `opens=1 plus_opens=1`, `gtk warnings: 0`. Then the Task 1 baseline diff and the slide-over/badges/tour-surface probes: **allowed baseline changes:** none beyond Tasks 1-2. A screenshot at 1400x900 (`GSK_RENDERER=cairo`, `import -window root`) to look at the bar once.
+
+- [ ] **Step 7: Commit**
+
+```sh
+git add -A src docs
+git commit -m "ui: one badge per enabled signal, an N signals overflow, and the order kept in memory"
+```
+
+---
+
+### Task 4: Badge drag (to a plot row, and to reorder); the list stops being a drag source
+
+**Files:**
+- Modify: `src/ui_badges.cpp`, `src/ui_signals.cpp`, `src/ui.cpp`, `src/ui_app.hpp`, `src/ui_probe.cpp`
+
+**Interfaces:**
+- Consumes: `on_drag_prepare(GtkDragSource*, double, double, gpointer)` (payload: the signal index as a decimal string), `DragContext{App*, size_t}`, `on_drop_channel` (the plot area's drop target, unchanged), `badge_order`, `signal_badges`.
+- Produces: nothing new in `ui_app.hpp` except removals.
+
+- [ ] **Step 1: The badge is a drag source and a reorder target (`make_signal_badge`)**
+
+Append to `make_signal_badge`:
+
+```cpp
+  // A drag handle: the same payload the list's rows used to carry, so the plot area's drop target takes it
+  // unchanged. The slide-over steps aside for the drag, since it covers the plot's right edge.
+  DragContext* ctx = new DragContext{&app, index};
+  GtkDragSource* source = gtk_drag_source_new();
+  gtk_drag_source_set_actions(source, GDK_ACTION_COPY);
+  g_signal_connect_data(source, "prepare", G_CALLBACK(on_drag_prepare), ctx,
+                        [](gpointer data, GClosure*) { delete static_cast<DragContext*>(data); },
+                        G_CONNECT_DEFAULT);
+  g_signal_connect(source, "drag-begin", G_CALLBACK(+[](GtkDragSource*, GdkDrag*, gpointer user) {
+                     slideover_close(*static_cast<App*>(user));
+                   }),
+                   &app);
+  gtk_widget_add_controller(b.button, GTK_EVENT_CONTROLLER(source));
+
+  // Dropping another signal's badge on this one moves it in front of this one.
+  GtkDropTarget* drop = gtk_drop_target_new(G_TYPE_STRING, GDK_ACTION_COPY);
+  g_signal_connect(drop, "drop", G_CALLBACK(on_badge_drop), &b);
+  gtk_widget_add_controller(b.button, GTK_EVENT_CONTROLLER(drop));
+```
+and, above it in the anonymous namespace:
+
+```cpp
+/// The reorder: widgets are moved, never rebuilt, so neither the dragged badge nor this target (whose "drop"
+/// emission is running) is destroyed under the drag.
+gboolean on_badge_drop(GtkDropTarget*, const GValue* value, double, double, gpointer user) {
+  Badge* target = static_cast<Badge*>(user);
+  App* app = static_cast<App*>(g_object_get_data(G_OBJECT(target->button), "udpscope-app"));
+  if (app == nullptr || !G_VALUE_HOLDS_STRING(value)) return FALSE;
+  const char* text = g_value_get_string(value);
+  const std::size_t signal = static_cast<std::size_t>(std::atoll(text ? text : "0"));
+  Badge* moved = nullptr;
+  for (auto& b : app->badges.signal_badges) {
+    if (b->signal == signal) moved = b.get();
+  }
+  if (moved == nullptr) return FALSE;
+  if (moved == target) return TRUE;
+  GtkWidget* prev = gtk_widget_get_prev_sibling(target->button);
+  if (prev != moved->button) {  // already directly in front: nothing to move
+    gtk_box_reorder_child_after(GTK_BOX(app->badges.signals_row), moved->button, prev);
+  }
+  // The order, as the widgets now stand.
+  app->badge_order.clear();
+  for (GtkWidget* c = gtk_widget_get_first_child(app->badges.signals_row); c != nullptr;
+       c = gtk_widget_get_next_sibling(c)) {
+    for (auto& b : app->badges.signal_badges) {
+      if (b->button == c) app->badge_order.push_back(b->signal_name);
+    }
+  }
+  return TRUE;
+}
+```
+`gtk_box_reorder_child_after(box, child, nullptr)` puts the child first, which is what a `nullptr` `prev` means here.
+
+- [ ] **Step 2: Remove the list's drag source (`rebuild_signal_list`)**
+
+Delete the `DragContext* ctx ...` block through `gtk_widget_add_controller(row, GTK_EVENT_CONTROLLER(source));` (~454-471). `grep -n row_drag_sidebar src` : if `rebuild_signal_list` was its only caller, delete `row_drag_sidebar`, its declaration and `App::sidebar_hidden_for_drag`; if something else calls it, leave it. Update the comment above the list's row loop that mentions dragging, if any.
+
+- [ ] **Step 3: The probes that drove the list's drag**
+
+`src/ui_probe.cpp` ~3843-3847 walks `signal_list` rows (read what it does: if it performs a drag or a drop by index, it now takes the index from `signal_badges[0]->signal` and calls `assign_signal_to_row` / `on_drop_channel` with the same payload). Keep every printed line it printed before.
+
+- [ ] **Step 4: Extend `signal_badges_probe`**
+
+After the existing line print a second:
+
+```
+[sigbadges] drag_sources=<number of badges with a GtkDragSource controller> drop_targets=<... GtkDropTarget> prepare_ok=<1 if on_drag_prepare for badges[0]'s DragContext returns a non-null provider> reorder_before=<names comma-separated> reorder_after=<...> reorder_ok=<1 if dropping the last badge on the first moved it to the front and badge_order matches the widget order> payload_drop=<1 if on_drop_channel-equivalent: assign_signal_to_row(badges[0]->signal, 0) leaves it plotted> list_drag=<number of GtkDragSource controllers on the first list row; must be 0>
+```
+Controllers are enumerated with `gtk_widget_observe_controllers()` (a `GListModel`) and `G_TYPE_CHECK_INSTANCE_TYPE`/`GTK_IS_DRAG_SOURCE`. With fewer than 2 badges print `reorder_ok=-1`. Drop the reordered badge back into its place at the end so later probes see the original order. For the `GValue`: `GValue v = G_VALUE_INIT; g_value_init(&v, G_TYPE_STRING); g_value_set_string(&v, std::to_string(signal).c_str());` and call `on_badge_drop` directly -- it is in the anonymous namespace of `ui_badges.cpp` where the probe lives, so no export is needed.
+
+- [ ] **Step 5: Verify**
+
+Build (zero warnings; `-Wunused` would flag a leftover `row_drag_sidebar`). UDPS run with `UDPSCOPE_ENABLE_ALL_MS=500 UDPSCOPE_PROBE_SIGNAL_BADGES_MS=1500`. Expected: `drag_sources == drop_targets == badges`, `prepare_ok=1`, `reorder_ok=1` (or `-1` if fewer than 2), `payload_drop=1`, `list_drag=0`, `gtk warnings: 0`, no `Gtk-CRITICAL`. Then the Task 1 baseline diff: **allowed changes:** a drag-by-list-row probe line that now reports through the badge (explain it). A real pointer drag cannot be simulated headless: say so in the report, and note that the drop path itself is `assign_signal_to_row` (probed in Task 2).
+
+- [ ] **Step 6: Commit**
+
+```sh
+git add -A src docs
+git commit -m "ui: the signal badge is the drag handle (to a plot row, or to reorder); the list rows stop dragging"
+```
+
+---
+
+### Task 5: Docs, the E-1608 run and the sweep of what the list's move touched
+
+**Files:**
+- Modify: `README.md`, `docs/claude/verification.md`, `docs/claude/probe-readings.md`, `docs/claude/invariants-plot-and-layout.md`, `docs/claude/architecture.md`, `docs/claude/invariants-gtk-and-chrome.md` (only if it names the list as being in the sidebar), `src/ui_tour.cpp` (badges step text), `SPECS.md` is **not** touched.
+
+- [ ] **Step 1: The E-1608 run (the spec's stress case)**
+
+```sh
+python3 tools/mock_e1608.py & MOCK=$!
+sleep 1
+xvfb-run -a -s "-screen 0 1400x900x24" sh -c 'GDK_BACKEND=x11 GSK_RENDERER=cairo UDPSCOPE_EXIT_AFTER_MS=7000 UDPSCOPE_ENABLE_ALL_MS=1500 UDPSCOPE_PROBE_SIGNAL_BADGES_MS=3000 ./build/udpscope --source e1608 --source-opt address=127.0.0.1 > /tmp/ui-signals-e1608.log 2>&1 & sleep 4.5; import -window root /tmp/ui-signals-e1608.png; wait'
+kill $MOCK
+grep -E '\[sigbadges\]|Gtk-|gtk warnings' /tmp/ui-signals-e1608.log
+```
+Expected: `overflow=1 overflow_text=<N> signals plus_visible=0`, `bar_h_fixed=1`, and `bar_min_w` equal to the UDPS run's (the scroller keeps it constant -- if it differs by more than the one badge's rounding, the scroller is not constraining: fix before going on). Look at the screenshot once: the "N signals" badge, Trigger and Source on the right, bar height unchanged. Then open the `signals` page from a probe or by `g`, activate a row (E-1608 has up to ~17): the page for it exists (`[signalpage]` run against the mock too: `UDPSCOPE_PROBE_SIGNAL_PAGES_MS=3000`). Kill the mock.
+
+- [ ] **Step 2: Docs**
+
+- `README.md`: the signals section describes the badge bar (signal badges, `+`, the six-badge overflow, drag to a plot or to reorder, the per-signal page) instead of the list in the sidebar; state that the order is kept for the session only.
+- `docs/claude/verification.md`: add `UDPSCOPE_PROBE_SIGNAL_PAGES_MS` and `UDPSCOPE_PROBE_SIGNAL_BADGES_MS` next to the badge probes; `docs/claude/probe-readings.md`: the `[signalpage]` line and the two `[sigbadges]` lines, each field with the value it must read and the defect a wrong reading names (the fields above).
+- `docs/claude/invariants-plot-and-layout.md`: one rule -- the badge bar's signal badges live in a scroller so the bar's minimum width never depends on the signal count (the E-1608 case), and the bar's height is fixed.
+- `docs/claude/architecture.md`: the page ids now implemented (`signals`, `signal:<name>`), `ui_signal_page.cpp`, and that the dock holds the cursors and measurements only. `docs/claude/invariants-gtk-and-chrome.md`: if it describes `outlive_the_rebuild` or the list's drag/sidebar hiding, say it now covers the signal page's buttons and that the list is no longer a drag source.
+- `src/ui_tour.cpp`: the `"badges"` step text becomes `"Setup is reached by the thing it configures. A badge per signal opens that signal's colour, calibration and plot; the + opens the full list; Trigger and Source open their own forms. Drag a signal badge onto a plot to draw it there, or onto another badge to reorder. Click again, press Esc or click the plot to close the panel."`
+
+- [ ] **Step 3: Final run**
+
+Build from scratch (`rm -rf build/CMakeFiles/udpscope.dir; cmake --build build -j 2>&1 | grep -c warning` -- expected exactly `1`, the icons' warning; if a clean rebuild is too slow, report the incremental result instead), the UDPS baseline diff, and the slide-over / badges / signal-pages / signal-badges / tour-surface probes once each. Report every baseline difference with its explanation.
+
+- [ ] **Step 4: Commit**
+
+```sh
+git add -A src docs README.md
+git commit -m "docs: the signal badges, the signal pages and the six-badge overflow (step 2 of the redesign)"
+```

docs/superpowers/plans/2026-11-03-ui-events-dock.md

@@ -0,0 +1,88 @@
+# Events in the dock, the left pane deleted -- Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Step 4 of the badges/dock redesign (spec `docs/superpowers/specs/2026-11-02-ui-badges-dock-design.md`): a compact Events section in the dock, the full events list and its actions on an `events` slide-over page, the left events pane / divider / header toggle deleted, and the Mallard manual, USER-GUIDE and remaining docs swept for the new layout.
+
+**Architecture:** The dock gets a third block under the readouts (`build_events_dock` in `src/ui_dock.cpp`): one compact row per `EventRecord` (title, time, small marker; no thumbnails), a "Manage" button, one click replays. The existing pane widgets (`events-pane.ui`: head with Live, Compare, Accumulate, the multi-select list with thumbnails) stop being a `GtkRevealer` beside the plot and become the content of the `events` slide-over page; the list keeps its builder, thumbnail cache and selection logic. Both views are rebuilt from the same `event_store->list()` by the same refresh entry point.
+
+**Tech Stack:** C++20, GTK4/libadwaita, the headless self-check probes (no unit tests).
+
+## Global Constraints
+
+- The dock is fixed at 280 px; dock event rows are ellipsized labels with fixed `width-chars`/`max-width-chars`; no thumbnails in the dock (layout must not depend on content).
+- No new overlay child; the page uses `slideover_add_page(App&, id, title, widget)`; the page id is `events`.
+- "Disable, do not hide": the dock's Events block stays on screen, insensitive, when unavailable. **Availability rule (deviation from the spec's "insensitive outside trigger mode", kept on purpose):** the existing `sync_events_availability` condition (`event_recording || replaying || events_cached`) -- a replay or a group leaves trigger mode, and a block that greys itself under the click that started it is the trap `invariants-trigger-and-pinning.md` records. Document the deviation in README and `docs/claude`.
+- A handler that rebuilds destroys the widgets it was emitted from: use `outlive_the_rebuild(widget)`. `refresh_events_pane` must keep nulling `events_thumb` before it removes children. `update_group_buttons` keeps its `app.window == nullptr` teardown guard.
+- `model->signals()` is read only under `model->mutex()`.
+- The page content is the pane's `events_box`, never the `GtkRevealer` (an unrevealed revealer measures 0x0).
+- Selection survives marking: `mark_events_on_screen` updates titles in place and now also updates the dock rows' marker; it never rebuilds the page list.
+- Every new source file carries the SPDX MIT header (this plan adds none).
+- Baselines: clean build = 1 warning (icons `-Woverlength-strings`), incremental = 0, `gtk warnings: 0`, no `Gtk-CRITICAL`. Probes need a tour-seen config for slide-over page legs (see `.superpowers/sdd/task-5-report.md`, `verification.md`). Mocks: `tools/mock_udpstreamer.py` (8114), `tools/mock_e1608.py` (54211); run serially, kill them.
+- The session file has no events-pane field (`events_pane_width` is memory only); there is nothing to migrate. README's claim that the width is remembered across sessions is wrong and is removed.
+
+---
+
+### Task 1: The Events block in the dock (the left pane still exists)
+
+Adds the dock block so the app stays whole; nothing is removed.
+
+**Files:**
+- Modify: `src/ui_dock.cpp`, `src/ui_app.hpp`, `src/ui_events.cpp`, `src/ui.cpp` (dock assembly, availability sync, tick), `src/ui_probe.cpp`, `CMakeLists.txt` (only if a file is added; none expected)
+
+**Interfaces:**
+- Produces (declared in `ui_app.hpp`, defined in `ui_dock.cpp`):
+  - `GtkWidget* build_events_dock(App& app);` -- vertical `GtkBox`: a row with the "Events" label and a "Manage" text `GtkButton` (calls `slideover_open(app, "events")`; a no-op until Task 2 registers the page), then a `GtkListBox` (`app.dock_events_list`, selection mode none, single-click activation) of compact rows, inside a `GtkScrolledWindow` with a fixed `min-content-height`/`max-content-height` (about 4 rows) and `vscrollbar-policy` automatic. Stores `app.dock_events_box`, `app.dock_events_list`, `app.dock_events_manage`.
+  - `void dock_rebuild_events(App& app);` -- clears and refills `dock_events_list` from `app.event_store->list()` (newest first, as the pane does): each row = a small marker label (`dock_event_marker`, see below), the title (ellipsized, same text as `event_row_title`), the time as the pane shows it (ellipsized, dim). With no records: one dim "no events yet" row. Attaches the `EventRecord` to the row as `"udpscope-event"` (same key as the pane). Null guard: a no-op before `build_events_dock` ran or when `app.event_store` is null.
+  - `void dock_mark_events(App& app);` -- updates each dock row's marker/title from the same data `mark_events_on_screen` uses (the event on screen and the group members), without rebuilding rows.
+  - `void dock_events_set_sensitive(App& app, bool available);` -- the one place the block's sensitivity is set; `sync_events_availability` calls it with its own `available` value.
+- Row activation (single click): calls the existing `replay_event(app, record)` that `on_event_row_activated` (`ui_events.cpp:961`) calls, with the same argument it passes; do not duplicate the replay logic -- extract the shared body if `on_event_row_activated` has any.
+- Consumes: `App::event_store`, `EventRecord`, `event_row_title()` (`ui_events.cpp:784`), `replay_event`, `mark_events_on_screen`, `slideover_open`.
+
+- [ ] **Step 1: Build the block.** Write `build_events_dock`, `dock_rebuild_events`, `dock_mark_events`, `dock_events_set_sensitive` in `ui_dock.cpp`. Marker: a single-character label -- the on-screen event gets a filled marker, the group members another, others none (read how `mark_events_on_screen` (`ui_events.cpp:796`) decides the on-screen/group titles and reuse its predicate; do not invent a second one). CSS: check `ui_widgets.cpp` for existing `.udpscope-event-*` classes and `dim-label` before adding any.
+- [ ] **Step 2: Wire it.** Append `build_events_dock` to the dock after the readouts box (and a separator), in `ui.cpp` where `build_readouts_dock` is assembled. Call `dock_rebuild_events(app)` at the end of `refresh_events_pane`'s non-empty and empty paths (every place it finishes) **and** from `record_event` unconditionally (today's `record_event` refreshes the pane only if the revealer is revealed; the dock must follow every latch), and `dock_mark_events` from `mark_events_on_screen`. Call `dock_events_set_sensitive` from `sync_events_availability` (`ui_events.cpp:40-70`) with its `available` result, and once after building (insensitive until available).
+- [ ] **Step 3: Probe.** In the existing events probe (`events_probe_next`, `UDPSCOPE_PROBE_EVENTS_MS`) print `dock events: rows=<n> pane_rows=<n> same_titles=<0|1> sensitive=<0|1> dock_w=<n>` after at least two latched events (the probe already produces them), where `same_titles` compares each dock title to the pane row's title label (`"udpscope-event-title"`) in order, and again after a replay (`on_screen` marker present on exactly one dock row). Add one click on a dock row to the probe and print `dock replay: clicked=<0|1> replaying=<0|1>` (the dock row click starts a replay as the pane's activate does).
+- [ ] **Step 4: Build; run** the events probe (UDPS mock), the readouts probes (regression), and check `dock_w` <= 280, `gtk warnings: 0`.
+- [ ] **Step 5: Commit** (`git add src/ui_dock.cpp src/ui_app.hpp src/ui_events.cpp src/ui.cpp src/ui_probe.cpp`; message `ui: compact events block in the dock`).
+
+---
+
+### Task 2: The `events` page; the left pane, divider and header toggle deleted
+
+**Files:**
+- Modify: `src/ui_events.cpp`, `src/ui.cpp`, `src/ui/main-window.ui`, `src/ui/header-bar.ui`, `src/ui/events-pane.ui`, `src/ui_app.hpp`, `src/ui_trigger.cpp` (`:597-601`, `:723-724`), `src/ui_layout.cpp` (`:380` comment), `src/ui_widgets.cpp` (`:58-60` comment), `src/ui_probe.cpp`, `src/ui_dock.cpp`
+
+**Interfaces:**
+- Consumes: Task 1's `build_events_dock`, `dock_rebuild_events`, `dock_mark_events`, `dock_events_set_sensitive`; `slideover_add_page`, `slideover_open`.
+- Produces: slide-over page `events` (title "Events") whose content is `events_box` of `events-pane.ui`; `build_events_pane(App&)` now returns that box (not a revealer); `App::events_revealer`, `App::events_divider`, `App::events_pane_width`, `sync_events_divider`, the header `events_toggle` and its handler are gone; `events_cached`/`sync_events_availability` keep driving the dock block's sensitivity (and the page's: set `events_box` insensitive with it).
+
+- [ ] **Step 1: The page.** `events-pane.ui`: drop the `events_pane` revealer so `events_box` is the root (rename nothing else); keep `events_head`, `events_live`, `events_compare`, `events_accumulate`, `events_list`. `build_events_pane` stops creating `events_revealer`. Register the page next to the `cursors`/`measure` registrations in `ui.cpp`: `slideover_add_page(*app, "events", "Events", app->events_box)` (add the `events_box` member if absent). `record_event`'s refresh condition `gtk_revealer_get_child_revealed` becomes "the `events` page is open" (`slideover_page(app) == "events"`), because the dock refreshes independently; opening the page (the slide-over's open path or the Manage button) must refresh the list once so it is current -- put this in a `slideover_set_on_open`-style hook only if the slide-over already has one; otherwise refresh in the Manage button's handler and in `refresh_events_pane` callers that run while closed (cheap; the list is small) -- state in the report which you chose.
+- [ ] **Step 2: Delete the pane.** `main-window.ui`: remove `events_divider`; `left_column` becomes the `side_view` content directly (keep every id inside it); fix the header comment (lines ~6, 23, 29). `ui.cpp`: remove `sync_events_divider`, its tick call, the `events_divider` creation (`~5201-5206`), the null guard (`~4998`), the toggle handler (`~4951-4959`) and the toolbar-order probe string entry (`~3010`); `header-bar.ui`: remove `events_toggle`; keep the `udpscope-events-symbolic` icon (used by `preferences.ui`). `ui_app.hpp`: remove the members and declarations (`events_divider`, `events_pane_width`, `events_revealer`, the toggle pointer). `sync_events_availability` loses the toggle/revealer branches, keeps computing `available`, and drives `dock_events_set_sensitive` plus the page's sensitivity. Fix the comments at `ui_trigger.cpp:597-601`, `:723-724`, `ui_layout.cpp:380`, `ui_widgets.cpp:58-60`.
+- [ ] **Step 3: Probes.** Rewrite `events_probe_next` (`ui_probe.cpp:5590-5860`) to open the page with `slideover_open(*a, "events")` instead of clicking the toggle, then drive selection/Compare/Accumulate exactly as before on the page's list; delete the divider/revealer/`pane_w` reads; rewrite `report_events_availability` (`ui.cpp:5712-5724`) as `[events] available=<0|1> dock_sensitive=<0|1> page_sensitive=<0|1> page=<id>` and the `events pane:` dump (`ui.cpp:6242-6255`) as `events pane: compare= accumulate= list= nested=` (no revealer). Any layout dump or toolbar probe naming the toggle is updated. The plot's width must no longer change when events exist: add `plot_w_stable=<0|1>` comparing the plot area's allocated width before and after the first latched event (it must read 1; the old pane squeezed it).
+- [ ] **Step 4: Run** the events probe, the trigger probes, the layout/toolbar probes, the readouts probes, one E-1608 run; `gtk warnings: 0`, no `Gtk-CRITICAL`, in particular none from `events_thumb`, `update_group_buttons` at teardown, or the removed revealer. Re-baseline `.superpowers/sdd/ui-signals-baseline-udps.txt` only where this step explains a difference.
+- [ ] **Step 5: Commit** (`git add` the modified files by name; message `ui: the events list is a slide-over page; the left pane, its divider and the header toggle are gone`).
+
+---
+
+### Task 3: Tour, context help, docs/claude, README
+
+**Files:**
+- Modify: `src/ui_tour.cpp`, `src/ui_context_help.cpp` (`:102-110`), `README.md` (97, 841-850, 883, 1032, 1194, 3025-3027), `docs/claude/{architecture,verification,probe-readings,invariants-gtk-and-chrome,invariants-trigger-and-pinning,invariants-plot-and-layout}.md`
+
+- [ ] **Step 1: Tour and help.** The `dock` tour stop text mentions the Events block (what it lists, that one click replays, that Manage opens the list). The context-help hints `events` (anchored to `&App::events_head`, now on a page) and `events_record` follow how the `cursors`/`measures` hints were handled in step 3 (anchor on the page heading, shown while the page is open; reword "the events pane"). Run the help-figures and tour probes.
+- [ ] **Step 2: docs/claude.** `architecture.md` (chrome section: the dock now has readouts and events; page `events`; `events` no longer "reserved", ~line 105), `invariants-gtk-and-chrome.md` (paned/revealer traps at ~212-228 lose the events divider; teardown ~281 and `events_thumb` ~297, thumb cache ~309 now say "the page's list"), `invariants-trigger-and-pinning.md` (~441-453: the availability rule drives the dock block's sensitivity; the spec's "outside trigger mode" deviation and why), `invariants-plot-and-layout.md` (no events divider; the plot is never squeezed by events), `verification.md` (~724 and the events probe wording), `probe-readings.md` (`dock events:`, `dock replay:`, the new `[events]` and `events pane:` lines and what each must read; the old `pane_w=240` rows and the `[events]` table near 1660-1675 rewritten).
+- [ ] **Step 3: README.** Layout/dock description, the header (no Events toggle), the events page, the single-click replay in the dock, deviations: availability rule instead of "outside trigger mode"; the dock list has no thumbnails (the page does); delete the false "remembers the width" claim; update the pending-removal note at ~3025-3027 (it is done).
+- [ ] **Step 4: Run** the tour and help-figure probes, one UDPS and one E-1608 run; `gtk warnings: 0`.
+- [ ] **Step 5: Commit** (code: `ui: tour and help describe the events block`; docs: `docs: events in the dock and on its page`).
+
+---
+
+### Task 4: The Mallard manual and USER-GUIDE sweep for the whole redesign
+
+**Files:**
+- Modify: `help/C/org.udpscope.app/*.page` (`trigger.page` 169-196 "Events pane on the left", the history button, "Drag the pane's edge"; `overview.page` incl. its layout description and any figure caption; `signals.page`, `math.page`, `sessions.page`, plus any page that mentions the side panel, the sidebar tabs ("Measure", "Signals" tab), the header's sidebar toggle, or the Events toggle), `docs/USER-GUIDE.md`, `README.md` leftovers
+
+- [ ] **Step 1: Find every stale mention.** `grep -rniE "side panel|sidebar|side pane|tab switcher|\bMeasure tab|Signals tab|events pane|history button|Events toggle|drag.*(edge|divider)" help/C docs/USER-GUIDE.md README.md src/ui_*.cpp` and read each hit in context; also check figures the manual embeds (`help/C/org.udpscope.app/figures/` and how they are generated -- `UDPSCOPE_*` help-figures probe in `verification.md`). List every hit and its disposition in the report.
+- [ ] **Step 2: Rewrite** each page to the real UI: header bar (time window, Trigger, Pause, Cursors, Dock toggle, menu), the plot, the badge bar (signal badges, `+`, N signals, Trigger, Source), the slide-over pages (trigger, signals, signal:<name>, cursors, measure, events, source), the dock (Readouts: cursors, measurements; Events). Read the code or `docs/claude/architecture.md` to be accurate; do not invent shortcuts (`m` toggles Measurements, `g` the signals page -- check `src/shortcuts.cpp`). Regenerate figures only if the repository already has a script that does so headlessly; otherwise say which figures remain stale.
+- [ ] **Step 3: Validate** the Mallard pages if `yelp-check` / `xmllint` is available (`xmllint --noout help/C/org.udpscope.app/*.page`); build with `cmake --build build -j` (the help may be compiled/installed by a target).
+- [ ] **Step 4: Commit** (`docs: the manual and the user guide describe the badge bar, the dock and the slide-over pages`).

docs/superpowers/plans/2026-11-03-ui-readouts-dock.md

@@ -0,0 +1,107 @@
+# Compact readouts dock -- step 3 of the badge-bar redesign Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** The dock shows the cursors and the measurements as compact, read-only readouts (about 280 px wide, always on screen); the full cursors panel and the full measurements panel (mode, reset, add, statistics, edit) become the `cursors` and `measure` slide-over pages, reached by an "Edit" text button in the dock, by the `m` key, and by clicking a measurement's dock line.
+
+**Architecture:** A new unit `src/ui_dock.cpp` (spec: `ReadoutsDock`) builds the dock's "Readouts" section: a cursors block (a small grid mirroring `App::cursors_lines`) and a measurements block (one line per `App::measures`). It owns no formatting: `update_cursors_pane()` and `update_measures()` already compute the strings, and they now write them to the page's widget *and* to the dock's, from the one string. `cursors_panel` and the measures panel are *reparented* (as the trigger form and the signal list were) into slide-over pages with ids `cursors` and `measure`. The dock's old contents (the two full panels) leave it.
+
+**Tech Stack:** C++20, GTK4, libadwaita >= 1.8, CMake. No unit-test suite: verification is the app's own headless self-check (`xvfb-run`, mock sources) -- extend `src/ui_probe.cpp` probes, never a separate harness.
+
+Spec: `docs/superpowers/specs/2026-11-02-ui-badges-dock-design.md` ("Right dock", "Slide-over panel", rollout step 3). Earlier plans: `2026-11-02-ui-badges-dock-shell.md` (step 1), `2026-11-03-ui-badges-signals.md` (step 2). Branch: `feature/ui-badges-dock` (continue on it).
+
+## Global Constraints
+
+Copied from the spec and the repository's rules; every task includes them.
+
+- **Right dock (spec, verbatim):** "Fixed width, about 280 px; always on screen, shown but insensitive until the stream has signals ('disable, do not hide'). It stays an `AdwOverlaySplitView` sidebar ... **Readouts** (top): the active cursor values and measurement values, read-only, one compact line per value, through the one formatter both panes share (`invariants-readouts-and-cursors.md`). An 'Edit' affordance opens the slide-over's `measure` or `cursors` page; clicking a measurement row opens that measurement's editor."
+- **One formatter:** a readout quotes a stored sample and never a value between two (`docs/claude/invariants-readouts-and-cursors.md`); the dock and the page show the *same string*, set from the same variable in the same call -- no second `format_measure()` call site for the same value.
+- **Layout must not depend on content** (`invariants-plot-and-layout.md`): the dock has a fixed width (280 px: `min-sidebar-width` = `max-sidebar-width` in `main-window.ui`), every dock label is ellipsized with a fixed `width-chars`/`max-width-chars`, so a long unit or value never widens the dock; the badge bar keeps its fixed height; the slide-over overlays and never resizes the plot.
+- **A `GtkOverlay` child is picked wherever its allocation is**: this step adds no overlay child.
+- Page ids: `trigger`, `signal:<name>`, `signals`, `measure`, `cursors`, `events`, `source-<id>`. This step adds `measure` and `cursors`. One slide-over page at a time; each page has its own scroller (`slideover_add_page` provides it); the open page is not saved.
+- "Disable, do not hide": with the cursors off, the dock's cursor block stays on screen with `--` cells (the existing blanking in `update_cursors_pane`), insensitive; an empty measurement list shows one dim line, never nothing.
+- Text buttons only for new controls ("Edit", not an icon). Existing icon buttons that move into the pages are not changed in this step.
+- The widget-lifetime trap (`invariants-gtk-and-chrome.md`): a click handler that calls `rebuild_measures_pane()` / `rebuild_cursors_pane()` destroys widgets it may have been emitted from; hold the emitter with `outlive_the_rebuild(widget)` first. The dock's lines are rebuilt by those two functions, so a click on a dock line must not be handled by a widget that the rebuild destroys synchronously (open the dialog from the handler, rebuild later).
+- Every new source file carries the SPDX MIT header (`// SPDX-License-Identifier: MIT` / `// SPDX-FileCopyrightText: 2026 Martino Ferrari`).
+- Baselines: a clean build emits exactly **one** warning (the icons' `-Woverlength-strings`), an incremental build **zero**; the dump's `gtk warnings:` reads `0`; no `Gtk-CRITICAL`/`Gtk-WARNING`.
+- Verification runs are short and serial; kill every mock you start (`tools/mock_udpstreamer.py` port 8114, `tools/mock_e1608.py` port 54211); seed a tour-seen config so the first-run tour does not close slide-over pages (see `.superpowers/sdd/task-5-report.md` for commands). Do not re-run to chase cosmetics.
+- Do not push, merge or amend. Commit per task on `feature/ui-badges-dock`.
+
+## Deliberate step-3 deviations from the spec (state them in the final report)
+
+- **The measurement editor stays a dialog window** (`open_measure_dialog`): the `measure` page holds the list, Add, the Statistics switch and each row's edit button, which open that dialog. Moving the dialog's form into the slide-over is not needed for the readouts and is not done here.
+- The `measure` and `cursors` pages hold the existing panels unchanged (heading, mode dropdown, reset, switch, grid / add, statistics, rows), so their content is not re-designed.
+- Dock cursor lines carry the same cells as the page's grid (`who`, A, B, delta), at a smaller size; they are not reduced to the time line only, because the modes that read per-row values would then have no readout on screen.
+
+## File Structure
+
+| File | Create/Modify | Responsibility |
+| --- | --- | --- |
+| `src/ui_dock.cpp` | Create | The dock's Readouts section: build, rebuild of the cursor lines and the measurement lines, the Edit buttons, the click-to-edit on a measurement line, the `[dock]` probe line. |
+| `CMakeLists.txt` | Modify | Add `src/ui_dock.cpp` next to `src/ui_badges.cpp`. |
+| `src/ui_app.hpp` | Modify | `App::DockCursorLine`, `App::dock_cursor_lines`, `App::dock_measure_labels`, `App::dock_readouts` widgets; declarations. |
+| `src/ui_cursors.cpp` | Modify | `update_cursors_pane()` writes each cell's string to the page and to the dock; the rebuild calls the dock's rebuild. |
+| `src/ui_measure.cpp` | Modify | `update_measures()` writes each reading to the page's label and to the dock's; `rebuild_measures_pane()` rebuilds the dock lines. |
+| `src/ui.cpp` | Modify | Pages `cursors` / `measure` registered; panels removed from `dock_page`; `dock_show_section()` removed; `ShowMeasure` opens the page; dock assembly. |
+| `src/ui/main-window.ui` | Modify | Dock width 280 (`min/max-sidebar-width`), `side_column` `width-request` 260, comments. |
+| `src/ui_tour.cpp`, `src/ui_context_help.cpp` | Modify | Steps / hints that pointed at the cursors and measurements panels in the dock now open the page (as the signals step does). |
+| `src/ui_probe.cpp` | Modify | Probes that walked, measured or scrolled the panels while they lived in the dock; the `dock:` readings. |
+| `README.md`, `docs/claude/*.md` | Modify | Task 3. (`USER-GUIDE.md` and the Mallard manual are spec step 4.) |
+
+---
+
+### Task 1: The compact readouts in the dock (panels still in the dock)
+
+The Readouts section is added at the top of the dock, above the existing full panels, so the app stays whole: nothing is removed yet. Both read from the same strings.
+
+**Files:**
+- Create: `src/ui_dock.cpp`
+- Modify: `CMakeLists.txt`, `src/ui_app.hpp`, `src/ui_cursors.cpp`, `src/ui_measure.cpp`, `src/ui.cpp` (dock assembly, ~line 5161), `src/ui_probe.cpp` (a `[dock]` line in an existing probe)
+
+**Interfaces:**
+- Produces (declared in `ui_app.hpp`, defined in `ui_dock.cpp`):
+  - `GtkWidget* build_readouts_dock(App& app);` -- the Readouts box (a vertical `GtkBox`: a "Readouts" heading; a cursors block = a row with the "Cursors" label and an "Edit" `GtkButton` (text), then a `GtkGrid` of dock cursor lines; a measurements block = a row with the "Measurements" label and an "Edit" button, then a vertical box of lines). Stores `app.dock_cursor_grid`, `app.dock_measures_box`, `app.dock_cursors_edit`, `app.dock_measures_edit`.
+  - `void dock_rebuild_cursors(App& app);` -- called at the end of `rebuild_cursors_pane()`: rebuilds `app.dock_cursor_lines` (one `DockCursorLine {GtkWidget *label,*a,*b,*d;}` per `app.cursors_lines`, same order) in `dock_cursor_grid`. The first row is the same header `cursors_header()` writes (`who`/A/B/delta), small.
+  - `void dock_rebuild_measures(App& app);` -- called from `rebuild_measures_pane()` after the page's rows: one line per `app.measures` (signal chip, type name ellipsized, value label), pushing the value label to `app.dock_measure_labels` (same index as `app.measure_labels`). With no measurements: one dim line "no measurements".
+  - `void dock_cursor_cell(App& app, std::size_t line, const std::string& a, const std::string& b, const std::string& d);` and `void dock_measure_value(App& app, std::size_t i, const std::string& text);` -- set the dock's labels; no-ops when the index is out of range (mid-rebuild).
+- Consumes: `App::cursors_lines`, `App::measures`, `App::measure_labels`, `measure_color()`, `chip_markup()`, `signal_color_index()`, `open_measure_dialog(App&, int)`, `slideover_open(App&, const std::string&)` (page ids used in Task 2; in this task the Edit buttons call it and the page may not exist yet -- `slideover_open` of an unknown id is a no-op; Task 2 registers the pages).
+
+- [ ] **Step 1: Dock widgets and rebuild functions.** Create `ui_dock.cpp` with the functions above. Fixed sizes: dock label `width-chars`/`max-width-chars` of 9 for value cells, ellipsize end, CSS class `caption` and `numeric` (check `ui_widgets.cpp` for the existing CSS before adding any). The whole Readouts box is the first child of `app.dock_page` (insert before the cursors panel with `gtk_box_prepend`).
+- [ ] **Step 2: One string, two widgets.** In `update_cursors_pane()` (`ui_cursors.cpp`) replace the `put(line.a, va)` etc. by a helper that sets the page cell and calls `dock_cursor_cell(app, index, va, vb, vd)`; do the same for the blanking branch (`"--"`). In `update_measures()` (`ui_measure.cpp`, the two `gtk_label_set_text(label, ...)` sites that also write `app.measure_text[i]`) call `dock_measure_value(app, i, text)` from the same variable. Never format twice.
+- [ ] **Step 3: Rebuild hooks.** `rebuild_cursors_pane()` (ui.cpp ~1564) ends with `dock_rebuild_cursors(app)`; `rebuild_measures_pane()` calls `dock_rebuild_measures(app)` before its final `update_measures(...)`. Both are no-ops until `build_readouts_dock` ran (null guards).
+- [ ] **Step 4: Assemble.** In `ui.cpp` where the dock is assembled (after `gtk_box_append(dock_page, measures_panel)`), prepend `build_readouts_dock(*app)` and add its separator. The Edit buttons call `slideover_open(app, "cursors")` / `slideover_open(app, "measure")`; clicking a measurement line (a `GtkGestureClick` on the line box, not on the value label which is selectable) calls `open_measure_dialog(app, i)` with the index stored in the widget data, as `measures_row`'s edit button does.
+- [ ] **Step 5: Probe.** Add to the existing cursors probe (find it with `grep -n "cursors" src/ui_probe.cpp`) and measures probe a reading proving the dock agrees with the page: print `dock cursors: lines=<n> page_lines=<n> same_text=<0|1>` and `dock measures: lines=<n> page_rows=<n> same_text=<0|1>` where `same_text` compares every dock label's text to the page label's text. Also `dock_w=<allocated width of the dock readouts box>` and assert it does not exceed the sidebar width. Run with 3 measurements and the cursors on in `Both` mode (cursors mode set via `rows->set_cursor_mode`).
+- [ ] **Step 6: Build, run the probes against `tools/mock_udpstreamer.py`, verify `same_text=1`, `gtk warnings: 0`.**
+- [ ] **Step 7: Commit** (`git add src/ui_dock.cpp CMakeLists.txt src/ui_app.hpp src/ui_cursors.cpp src/ui_measure.cpp src/ui.cpp src/ui_probe.cpp`; message `ui: compact cursor and measurement readouts at the top of the dock`).
+
+---
+
+### Task 2: The `cursors` and `measure` pages; the dock is only readouts
+
+**Files:**
+- Modify: `src/ui.cpp`, `src/ui/main-window.ui`, `src/ui_app.hpp`, `src/ui_probe.cpp`, `src/ui_dock.cpp`
+
+**Interfaces:**
+- Consumes: Task 1's `build_readouts_dock`, `slideover_add_page(App&, id, title, widget)`, `slideover_toggle(App&, id)`.
+- Produces: slide-over pages `cursors` (title "Cursors", content `app.cursors_panel`) and `measure` (title "Measurements", content the measures panel); `AppAction::ShowMeasure` toggles the `measure` page; `dock_show_section()` and its declaration/uses are deleted.
+
+- [ ] **Step 1: Register the pages** next to the `trigger` and `signals` registrations (`ui.cpp` ~5156): `slideover_add_page(*app, "cursors", "Cursors", app->cursors_panel)` and `slideover_add_page(*app, "measure", "Measurements", measures_panel)`. Remove both `gtk_box_append(dock_page, ...)` of the panels and the separator between them; the dock keeps only `build_readouts_dock` (and, later, step 4's events).
+- [ ] **Step 2: Keys and actions.** `AppAction::ShowMeasure` -> `slideover_toggle(app, "measure")`. Delete `dock_show_section()`. Make sure the tour/help code does not call it (`grep -n dock_show_section src`).
+- [ ] **Step 3: Dock width.** `main-window.ui`: `min-sidebar-width`/`max-sidebar-width` 280, `side_column` `width-request` 260; update its comments.
+- [ ] **Step 4: Badge/header state.** The page ids join the "open" bookkeeping: `slideover_page(app)` reports them; nothing in the badge bar marks them (no badge). The header's Cursors toggle still mirrors the `cursors_switch` inside the page (both exist).
+- [ ] **Step 5: Probes.** Fix every probe that read the panels' allocation, sensitivity or scroll position while they sat in the dock (`dock_section_probe`, the `dock:` reading in the layout dump, the `cursors=... in the toolbar, dock=..., reset=... in the cursors pane` line, any that walks `dock_page`): they open the page first or read the widget tree without allocation. Add `[readouts] pages cursors=<0|1> measure=<0|1> dock_children=<n> dock_w=<n>` (pages registered; dock holds only the readouts box; width 280). Re-baseline `.superpowers/sdd/ui-signals-baseline-udps.txt` only where this step explains the difference.
+- [ ] **Step 6: Run** the UDPS and E-1608 probe runs serially; `gtk warnings: 0`; Esc closes the pages; the measure Add and the measurement dialog still work from the page (the existing measure probes).
+- [ ] **Step 7: Commit** (`ui: the cursors and measurements panels are slide-over pages; the dock is the readouts`).
+
+---
+
+### Task 3: Tour, context help, docs
+
+**Files:**
+- Modify: `src/ui_tour.cpp`, `src/ui_context_help.cpp`, `README.md`, `docs/claude/{architecture,verification,probe-readings,invariants-plot-and-layout,invariants-readouts-and-cursors,invariants-gtk-and-chrome}.md`, `help/C/*.page` mentions of the cursors / measurements panels in the dock or the side panel (the full Mallard sweep and `USER-GUIDE.md` are step 4)
+
+- [ ] **Step 1: Tour.** Steps pointing at `cursors_panel`/`cursors_head`/`measures_head`/`side_box` now target the dock's readouts, or open the `cursors` / `measure` page through the existing "tour opens a page" mechanism (`invariants-gtk-and-chrome.md`), as the signals step does. Rewrite the step text: readouts in the dock, "Edit" opens the page.
+- [ ] **Step 2: Context help.** Hints attached to `cursors_head` / `measures_head` live in the pages: show only while the page is open, or re-attach to the dock block headings -- whichever the existing layer supports without a second code path (follow how `signals_head` was handled). Run the help-figures probe and the tour probe (`UDPSCOPE_PROBE_*` in `verification.md`) and keep their lines sane.
+- [ ] **Step 3: Docs.** README (layout, keys, the dock, readouts, deviations listed above), `architecture.md` (chrome section), `verification.md` and `probe-readings.md` (new `[dock]`/`[readouts]` lines, changed `dock:` readings), `invariants-readouts-and-cursors.md` (the dock and the page share one string: rule and why), `invariants-plot-and-layout.md` (dock width 280, ellipsized cells).
+- [ ] **Step 4: Run** the tour/help-figure probes and one E-1608 run; confirm baselines (build 0 warnings, `gtk warnings: 0`).
+- [ ] **Step 5: Commit** (`docs: the readouts dock, the cursors and measurement pages`).

docs/superpowers/specs/2026-10-14-sidebar-tabs-design.md

@@ -0,0 +1,199 @@
+<!-- SPDX-License-Identifier: MIT -->
+<!-- SPDX-FileCopyrightText: 2026 Martino Ferrari -->
+
+# A tabbed side panel, and one channel list: design
+
+The side panel stacks five sections in one scrolling column — trigger, cursors, measurements,
+math, signals — each behind a `GtkRevealer` opened by its own toolbar toggle. With trigger,
+measurements, cursors and math all open the column is unusable: every section is short of room,
+and finding one means scrolling past three others.
+
+Two changes, aimed at that one problem:
+
+1. **The column becomes two tabs.** *Measure* holds the cursors readout and the measurements;
+   *Signals* holds the trigger and the channel list. One tab is on screen at a time, so no
+   section competes with four others for height.
+2. **The math list is folded into the signal list.** A math channel already *is* a channel in
+   the model, and the two lists were the same list drawn twice. One list, with a `MATH`
+   divider in it.
+
+A third change falls out of the first. A tab is one-of-N, so it can no longer carry an on/off:
+**no toggle hides a pane any more.** Trigger-off and cursors-off put their pane in a disabled
+state and leave it where it is.
+
+## The decisions taken, and what each one rules out
+
+| Decision | Alternative rejected |
+| --- | --- |
+| `AdwViewStack` + `AdwViewSwitcher` | `GtkStack` + `GtkStackSwitcher`: plain buttons beside an `AdwOverlaySplitView`, which is what the sidebar already is. `GtkNotebook`: draws its own tab strip, which costs width in a 320 px sidebar and reads as off-platform. libadwaita ≥ 1.8 is already a hard requirement (`CMakeLists.txt:22`), so the platform widget costs nothing new |
+| **A scroller per page**, inside the stack | One shared scroller around the stack: the two pages are different heights, so a tab switch would leave the scroll position somewhere the new page did not ask for |
+| The switcher sits **above** the scrolled area | Inside it: the one control that chooses what you are looking at must not be the first thing to scroll away |
+| **Two** tabs, exactly as grouped | A tab per section (five tabs): that is the stack again, laid sideways, and a 320 px sidebar has no room for five switcher pills. Measurements read what the cursors bracket, and the trigger picks a channel from the list beside it — the grouping follows the way the panes are used |
+| Nothing inside a tab collapses | Keeping a revealer per section inside the tab, or a `GtkPaned` between them: the first reintroduces exactly the state-management the tabs remove, two sections at a time instead of five; the second adds a divider position to persist per tab for a column that already scrolls |
+| Trigger-off and cursors-off **disable** their pane | Hiding it, which is today's behaviour: a pane you can see is a pane you can read, and the settings you are about to turn back on should not vanish while you look for them |
+| The `measurements` and `math` toolbar toggles are **deleted** | Keeping them as tab selectors: two buttons that select the same tab, whose pressed state duplicates the switcher's |
+| The switcher shows **titles only**, and the two icons the deleted toggles used are **removed** | Giving each page an `icon-name`: the measurements icon would carry over, but *Signals* has no glyph — reusing the trigger icon for a page that is mostly a channel list misnames it, and drawing a new one is new artwork under the icon authoring rules for a label two words long |
+| One row widget for both kinds of channel, differing **only in its menu** | Inline edit and delete buttons on math rows (today's math pane): math rows then carry visibly more controls than signal rows, and the list stops reading as one column |
+| A `+` on the `MATH` divider **only** | A `+` on the signals header too: a signal comes from CONFIG and cannot be added, so the button would have nothing to do |
+| The statistics accumulator keeps running on the **hidden** page | Gating `update_measures()` on the visible tab: the accumulator is history, so min/max/avg would gain a gap for exactly as long as you looked at the trigger |
+| The probe reads the **page name and sensitivity** | Dropping the two revealer readings: the defect they catch — a panel that is built but not on screen — still exists, it is just spelled differently |
+
+## 1. The container
+
+The sidebar child of `side_view` becomes a vertical `GtkBox`:
+
+```
+AdwOverlaySplitView.side_view
+  sidebar: GtkBox (vertical)
+    AdwViewSwitcher                      <- never scrolls
+    AdwViewStack
+      page "measure"  GtkScrolledWindow -> GtkBox: cursors, separator, measurements
+      page "signals"  GtkScrolledWindow -> GtkBox: trigger, separator, signal list
+```
+
+`side_scroll` moves inside the pages; `App::side_box` becomes the stack, and the five revealer
+fields in `ui_app.hpp` are removed with the code that sets them (`ui.cpp:4728-4767`).
+
+The switcher carries the two page titles and no icons. `udpscope-measure-symbolic` and
+`udpscope-math-symbolic` lose their last user with the toggles that used them, so both leave
+`src/icons/scalable/actions/` and `udpscope.gresource.xml`: the bundled set goes from six
+action icons to four, which `invariants-gtk-and-chrome.md` counts and must be corrected with
+the change.
+
+The pages are built by the functions that build them today — `build_trigger_panel()`,
+`build_cursors_panel()`, `build_measures_panel()`, `build_signal_panel()` — unchanged except
+that they are appended to a page's box instead of to a revealer.
+
+## 2. State instead of visibility
+
+| Control | Today | After |
+| --- | --- | --- |
+| `trigger_toggle` | trigger mode on/off **and** reveals the trigger pane (`ui_trigger.cpp:198`) | trigger mode on/off; the pane's body goes sensitive/insensitive |
+| `cursors_toggle` | cursors on/off **and** reveals the readout (`ui_cursors.cpp:124-126`) | cursors on/off; the readout goes insensitive and its values blank to `—` |
+| `cursors_reset` | hidden while cursors are off (`ui_cursors.cpp:122`) | insensitive while cursors are off |
+| `measures_toggle` | reveals the measurements (`ui.cpp:4541-4550`) | **deleted** |
+| `math_toggle` | reveals the math pane (`ui.cpp:4551-4558`) | **deleted** |
+| `sidebar_toggle`, `events_toggle`, `pause_button` | — | unchanged |
+
+The two deleted toggles leave `src/ui/header-bar.ui` with their handlers, so the bar is
+declared with five controls and no id resolves to a button nothing listens to.
+
+`update_side_visibility()` (`ui.cpp:2830-2850`) keeps its job — the whole sidebar is still the
+split view's to show, still gated on a CONFIG having named a signal — minus the line that showed
+`signal_toggle`, which no longer exists.
+
+Everything else those handlers do is untouched: `tc.armed`, the epoch rule and the
+`set_time_window()` call in `on_trigger_toggled()`, `sync_events_availability()`, the
+Arm/Disarm label, and `rows->set_cursors_visible()` with its `reset_cursors()`.
+
+Blanking the cursor readout to `—` rather than leaving the last values is the readout invariant
+restated: a readout quotes a stored sample, and with the instruments off there is no sample it
+quotes.
+
+## 3. One channel list
+
+**The duplication is literal, and the merge is mostly a deletion.**
+`rebuild_signal_list()` is handed `model.signals()`, and `append_math_signals_locked()`
+(`model.cpp:252-269`) has already appended one synthetic entry per math channel — *"they go
+through the ordinary signal path on purpose: a derived channel is a channel"*, says its own
+comment. Nothing in the list filters `sig.math`, so **every math channel is already a row in
+the signal list**, with its tick, chip, name, unit and menu. The math pane listed the same
+channels a second time.
+
+What the list gains:
+
+- a non-selectable `MATH` divider row before the first math row, carrying the `+` that opens
+  the node editor on a new channel;
+- two items in a math row's menu.
+
+| | signal row | math row |
+| --- | --- | --- |
+| tick | acquire (hidden in a file view) | enabled |
+| colour chip | clickable while plotted | unchanged |
+| unit | from CONFIG | the channel's own |
+| menu | Information, Default colour, Calibrate… | **Edit graph…**, Default colour, **Delete** |
+
+Information and Calibrate… are a *streamed* signal's — calibration is applied at ingest — so a
+math row carries neither. No rename item either: the node editor owns a math channel's name and
+unit (`src/ui/math-editor.ui:37-43`), so *Edit graph…* is where both are changed, and a second
+place to change them would be a second answer to the same question.
+
+Two things already work and must not be rebuilt: the tick is already the right switch —
+`enable_locked()` (`model.cpp:626-639`) mirrors it into the `MathChannel`'s own `enabled` flag —
+and the row's `GtkDragSource` already lets a math channel be dropped onto a plot row, which is
+how `math1` reached row 0 in the session this work started from.
+
+One defect to fix while merging: `App::math` is the copy the session file is written from, so a
+tick on a math row must mirror `enabled` into it before `schedule_layout_save()`. Today the pane's
+checkbox did that (`ui.cpp:2276`) and the list's tick did not, so the two controls disagreed
+about what gets saved.
+
+Deleted: `build_math_panel()` (`ui_math.cpp:1044`), `rebuild_math_pane()` (`ui.cpp:2251-2319`),
+`src/ui/math-panel.ui` and its entry in `src/ui/udpscope-ui.gresource.xml`, `App::math_revealer`,
+`App::math_list`, `App::math_toggle`, `App::measures_toggle`, `App::signal_revealer`, and
+`App::signal_toggle` with `on_signals_toggled()` (`ui_signals.cpp:303-307`) and its overflow-menu
+row (`ui.cpp:4452-4455`) — the list is a page now, so "show or hide the signal list" has nothing
+to hide. The node editor dialog itself is untouched; only the button that opens it moves.
+
+## 4. Persistence
+
+One key, top level in the session file beside `window_s` and `measure_stats`
+(`layout_store.cpp`):
+
+```toml
+side_tab = "signals"   # or "measure"
+```
+
+Written on save; applied once where the rest of the layout is applied, so an unknown or missing
+value leaves the stack on its first page. Nothing else about the panel is persisted today and
+nothing else needs to be: no revealer states remain, and the 320 px width is still the `.ui`'s.
+
+## 5. What runs on a hidden page
+
+`update_cursors_pane()` and `update_measures(force=false, accumulate=true)` are called every
+frame from the tick (`ui.cpp:3275-3276`) and keep being called whichever page is current.
+Writing a label on an unrealized widget is legal; **reading its allocation is not**. Every
+allocation read in the sidebar is a debug capture — `dbg_measures_pane_w/h`
+(`ui.cpp:3237-3239`), `dbg_signal_w/h` and `dbg_trigger_w/h` (`ui_probe.cpp:77-80`) — and each
+reads 0 on the page that is not current. That is a change in what the reading means, which §6
+handles; it is not a defect, and no functional code may start depending on those numbers.
+
+This is the revealer trap in a new widget. `invariants-gtk-and-chrome.md:174-181` records that
+an unrevealed `GtkRevealer` measures 0×0 and is still given the leftover width; a stack's
+hidden page measures 0×0 too, and the rule it teaches — ask about *state*, not about size —
+carries over unchanged.
+
+## 6. Verification
+
+Readings that change, and what each must say instead:
+
+| Reading | Was | Becomes |
+| --- | --- | --- |
+| `dbg_signal_revealed` (`ui_probe.cpp:90`) | the signal revealer's child is revealed | the `signals` page is current **and** its list is non-empty |
+| `dbg_trigger_revealed` (`ui_probe.cpp:92`, `:2190`) | the trigger revealer's child is revealed | the `signals` page is current **and** the trigger body is sensitive |
+| `dbg_measures_pane_w/h` | the pane's size while revealed | the pane's size while its page is current; 0 otherwise, and read as such |
+| the panel-toggle reading (`ui_probe.cpp:104`) | both menu toggles are visible | the switcher is visible, which is the one control those two became |
+
+One new probe, `UDPSCOPE_PROBE_SIDE_TAB_MS`: select the page that is not current, then dump the
+page name, the measurement row count and the accumulator's sample count. The count must have
+advanced across the switch — that is the §5 rule under test, and the defect it names is a
+statistics pane that silently restarts its history every time you look at the trigger.
+
+New reading for the merged list, on the existing signal-panel probe: the row count must be
+signals + 1 + math channels, and the math rows must carry the same widget shape as a signal
+row. A count short by the divider is a list that lost its `+`.
+
+Baselines, unchanged and re-read on every run: exactly four warnings on a clean build, no
+`Gtk-CRITICAL`, `test-ui` 15/15.
+
+Docs to update with the work: `probe-readings.md` (the three changed lines and the two new
+ones), `verification.md` (a bullet for the tab switch), `invariants-gtk-and-chrome.md` (the
+sidebar is a view stack, the hidden-page trap replaces the unrevealed-revealer one for it, the
+bar carries five controls and the bundled set four action icons),
+`invariants-math-channels.md` (the list lives in the signal panel), `invariants-readouts-and-cursors.md`
+(the readout blanks when the instruments are off), and a README note recording the deviation
+from `SPECS.md` where it names the panes.
+
+## Out of scope
+
+The events pane left of the plot, export, the node editor's internals, and the status bar.

docs/superpowers/specs/2026-10-31-e1608-source-design.md

@@ -0,0 +1,153 @@
+# MCC E-1608 source plugin (sub-project 3 of 4)
+
+Date: 2026-10-31
+Branch: `feature/source-e1608` (from `feature/source-plugins`, sub-project 1)
+
+## Context
+
+Sub-project 1 added the `DataSource` / `SourceKind` / `SourceRegistry` framework and ported
+UDPS onto it. This sub-project adds a second kind, `e1608`: the Measurement Computing E-1608
+Ethernet DAQ (8 SE / 4 DIFF 16-bit analog inputs, 2 analog outputs, 8 DIO bits, one 32-bit
+counter), with its own connect form and two side-stack panels.
+
+References for the wire protocol, both written by the user:
+
+- Primary: `~/Projects/marte2_projects/MCC_E1608_DataSource`, a MARTe2 DataSource
+  (`E1608DataSource.{h,cpp}`, `E1608ScanFifo`). Its class comment in the header is the
+  authoritative list of parameters and behaviour. It is bound to MARTe2 (`BasicTCPSocket`,
+  `StreamString`, `SingleThreadService`), so it is **ported** to plain C++, not linked.
+- Cross-check: `~/Projects/uopi/internal/datasource/mcc/{protocol,e1608}.go`, an independent
+  Go implementation of the same protocol.
+
+No board is available. The mock is the only verification until one is attached.
+
+## Decisions
+
+| Question | Decision |
+| --- | --- |
+| DAC / generator | Static level plus a software waveform (sine, square, triangle, ramp), 10 Hz at most. Runs as a timer inside `poll()`; no extra thread. |
+| Hardware | None available. A protocol mock (`tools/mock_e1608.py`) is the contract. Commands whose layout rests on a single reference (or where the two disagree) are listed as unverified. |
+| Analog input config | Full: per-channel enable and range, global SE/DIFF, MAC discovery, external clock, trigger, DI/counter poll rate. |
+| Digital lines and counter | Plot channels the user chooses, off by default, enabled per line in the connect form. |
+| Acquisition modes | Hardware-paced only (scan rate or external clock). Software-paced mode (`ScanRate = 0`) is not ported. |
+| Structure | Three layers: link, device, source. The bottom two have no GTK or `DataSource` types. |
+
+## Design
+
+### 1. Files (new, `src/source/e1608/`, plus the mock)
+
+- `e1608_link.{hpp,cpp}`: UDP discovery (broadcast, or a unicast sweep of a given subnet
+  matched by MAC and the E-1608 product id) and connection-code handshake; TCP command
+  framing with a timeout; the scan socket on `port + 1`. Plain POSIX sockets.
+- `e1608_device.{hpp,cpp}`: typed commands (AI, AO, DIO read/write/direction, counter
+  read/reset, scan queue, scan start/stop, status), the factory calibration read from the board's
+  calibration memory, and `decode()`, which turns raw interleaved `uint16` scans into calibrated
+  volts (`double`).
+- `e1608_source.{hpp,cpp}`: the `DataSource`: the `poll()` state machine, `Frame` building, the
+  DI/counter and generator timers, the atomic readouts for the panels.
+- `e1608_kind.cpp`: the `SourceKind`: the connect form and the two panels.
+- `tools/mock_e1608.py`: the protocol mock.
+- `register_builtin_sources()` registers `e1608` after `udps`.
+
+### 2. Data path and threading
+
+Everything runs inside `poll()` on the producer thread. The GTK thread reaches the board only
+through `post(Command)`.
+
+`poll(timeout)`:
+
+1. Drains the posted commands (DAC writes, DIO toggles, counter reset, generator edits).
+2. Runs the connection state machine: optional MAC lookup, handshake, calibration read, DIO
+   direction and initial outputs, scan queue and scan start take Disconnected to Scanning. A
+   link error fires `on_event(Disconnected)` and retries every 2 s. A connect attempt can block
+   `poll()` for up to the command timeout; that delays only the command queue.
+3. Waits on the scan socket for at most the time to the next timer, reads what arrived, keeps a
+   partial scan for the next call, decodes the complete scans with the calibration and
+   delivers a `Frame`.
+4. Runs the due timers: the DI/counter poll (`DiPollRate`) is a command round trip; the
+   generator tick (at most 10 Hz) is a DAC write.
+
+The frame:
+
+- Signals: the enabled AI channels (unit `V`, `range_min`/`range_max` from the channel's range),
+  the DI lines the user chose (0/1), and the counter if chosen.
+- All signals are scalar; `num_samples` is the number of scans decoded in that read.
+- DI and counter values are held across the block (a step trace).
+- `sampling_rate` is the scan rate on every signal. `counter` is a running frame count.
+- The aggregate rate (enabled channels times scan rate) must stay at or below 250 kS/s. The
+  form refuses a configuration above it.
+
+Overrun: if the board reports a scan overrun the source fires `on_event(Error)` and restarts
+the scan when `AutoRestart` is set; the next frame carries `lost = 1`. This is approximate,
+because the board does not report how many scans it dropped.
+
+Panel readouts: the source keeps the live DIO inputs, the counter, the DAC levels and the
+generator state in atomics. The panels read them from a GTK timer, so no widget touches the
+source's internals.
+
+### 3. Connect form and panels
+
+Connect form: grouped `AdwExpanderRow`s in the chooser's group. `SourceConfig` stays flat; a
+per-channel setting is a key such as `ai0=BIP10V` (absent means off).
+
+- Connection: address, MAC, discovery subnet, port, connection code, timeout. `valid()` needs
+  an address, or a MAC plus a subnet.
+- Acquisition: scan rate, external clock, trigger mode, auto-restart, calibrate (default on),
+  DI/counter poll rate.
+- Analog inputs: global SE or DIFF mode and 8 channel rows (enable, range). In DIFF mode rows
+  4 to 7 are insensitive, not hidden. `valid()` also enforces the 250 kS/s aggregate.
+- Digital I/O: direction per bit (I or O), a "plot" switch per input bit, a "plot counter"
+  switch, the initial DO value and the initial DAC levels.
+
+`identity()` is the address, or the MAC when there is no address. A session file is named
+`e1608-<identity>`, port 1, as sub-project 1 defines for non-UDPS kinds. `has_datagrams()` is
+false, so the capture button is disabled.
+
+Two side-stack panels, both insensitive while disconnected (disabled, not hidden):
+
+- Analog out: per DAC, a mode (Level, Sine, Square, Triangle, Ramp), a level or amplitude plus
+  offset, a frequency of 0.1 to 10 Hz, and an on/off switch. It shows the last voltage written
+  and clamps to ±10 V. The generator stops on disconnect and the DACs return to their initial
+  levels on reconnect.
+- Digital I/O: eight bit rows; an input bit shows a live LED, an output bit has a toggle that
+  posts a write. The counter shows its value and a Reset button. Directions come from the form
+  and are not changed at runtime.
+
+Tab icons are chosen in the plan under the project's bundled-icon rules.
+
+### 4. Verification
+
+Mock (`tools/mock_e1608.py`): UDP discovery with a MAC and the connection-code handshake; TCP
+commands for AI, AO, DIO, the counter, scan queue, scan start/stop, calibration memory and
+status; a scan stream on port+1 at the requested rate with a sine per channel; switches to drop
+the link after N seconds and to report an overrun. Its header lists every command whose layout
+is unverified (single reference, or the references disagree).
+
+Probe `UDPSCOPE_PROBE_E1608=<delay ms>`, run against the mock with `--source e1608`, extends the
+probe/dump in `src/ui.cpp`. It checks:
+
+- Frames arrive with the expected channel count and sample rate.
+- The panels are present and insensitive while disconnected.
+- A DAC write, a DIO toggle and a counter reset each reach the mock.
+- A forced link drop leads to a reconnect and a resumed stream.
+- The calibration is applied (the mock serves non-trivial coefficients).
+
+A decode check needs no mock: a fixed raw buffer decoded against hand-computed volts.
+
+Baselines are unchanged: the UDPS self-check reads as on `main`, exactly three build warnings,
+no `Gtk-CRITICAL`.
+
+Errors: a rejected handshake (bad connection code), no device found, timeouts and scan-socket
+loss surface through `on_event(Error)` with a readable message and follow the reconnect cycle.
+A rejected connection code stops the retries: the source stays in Error with that message until the user reconnects.
+
+Docs: update `architecture.md`, `build-and-run.md`, `verification.md`, `probe-readings.md` and
+`README.md`.
+
+## Out of scope
+
+- Software-paced acquisition (`ScanRate = 0`).
+- A generator faster than 10 Hz, and a dedicated I/O thread.
+- Changing DIO directions at runtime.
+- Per-channel SE/DIFF mixing (one global mode).
+- Verification against a real board.

docs/superpowers/specs/2026-10-31-source-plugins-design.md

@@ -0,0 +1,127 @@
+# Source plugins: framework and UDPS port (sub-project 1 of 4)
+
+Date: 2026-10-31
+Branch: `feature/source-plugins`
+
+## Context
+
+udpscope reads exactly one kind of source, a UDPStreamer stream through `deps/udpsclient`.
+The goal is to accept several kinds of data source as plugins, each with its own config
+dialog and, where the hardware offers it, its own UI (signal generator, digital I/O,
+multiple timebases).
+
+The work is split into four sub-projects, each with its own spec, plan and implementation:
+
+1. **Plugin framework + UDPS client ported onto it** (this document).
+2. Flat UDP plugin (standard MARTe2 UDPWriter stream; the wire format must be supplied or
+   located before that spec is written -- none was found in `~/workspace` or `~/Projects`).
+3. MCC E-1608 plugin. The protocol code in `MCC_E1608_DataSource` is bound to MARTe2
+   (`BasicTCPSocket`, `StreamString`, `SingleThreadService`); it is ported to plain C++, not
+   linked against MARTe2. AI streaming, DIO and DAC/generator panels.
+4. ABScope plugin. Needs a multi-timebase data path and a wire format: the ABScope design
+   only sketches the UDP header and `streamerd` is unwritten.
+
+Sub-project 1 changes no UDPS behaviour. It is a refactor plus the hosting machinery the
+later plugins need.
+
+## Decisions
+
+| Question | Decision |
+| --- | --- |
+| What "plugin" means | Compiled-in registry; the interface is kept clean enough for a `dlopen` loader to be added later (not built now). |
+| Threading | `Acquisition` keeps the single producer thread and calls `source->poll()`. UI actions reach the source through a thread-safe command queue drained inside `poll()`. CLAUDE.md's two-thread rule holds. (A per-source I/O thread was considered and deferred.) |
+| Source UI | Widget factory: a source returns `GtkWidget*` for its config form and each capability panel. |
+| Timebases in the frame | The neutral frame is single-timebase. Sub-project 4 extends interface and data path together; this may break the interface once, accepted. |
+| CLI / sessions | `--server/--port/...` keep meaning UDPS; `--source NAME` and `--source-opt k=v` added. Sessions keyed by kind + identity; legacy `host_port.toml` read as `udps`. |
+
+## Design
+
+### 1. The source interface (new `src/source/`)
+
+- **`SourceConfig`**: ordered string key/value map with typed getters. It is the stored form
+  (a TOML table), the `--source-opt` form, and what a config widget reads and writes.
+- **`Frame`**: source-neutral, mirrors `udps_frame_t`: `counter`, `lost`, `late`,
+  `recv_time`, `publish_mode`, `num_samples`, `signals[]` (the existing `SignalInfo`) and
+  `values[]` (doubles). `signals` and `values` are pointers into the source's own buffers,
+  valid only for the duration of `on_data`; `Acquisition` copies what it keeps. The hole, backfill and time-base logic needs `counter/lost/late`; a
+  source with no counter supplies a running counter and `lost = 0`. `Frame::value(sig, k,
+  col)` replaces `udps_frame_value`.
+- **`DataSource`**: the per-connection object.
+  - `open()`, `poll(timeout_ms)`, `close()`.
+  - `stats()` returns the counters now in `StreamStats`; `connected()` reports link state.
+  - `post(Command)`: thread-safe queue, drained inside `poll()`. `Command` is
+    `std::function<void()>`.
+  - `set_datagram_tap(fn)`: optional; lets UDP-based sources feed the raw-packet capture.
+  - Output goes to a `SourceSink` (`on_config`, `on_data`, `on_event`) called inside
+    `poll()`, as `udps_client` does today.
+- **`SourceKind`**: factory and UI description of one plugin type: `id`, `display_name`,
+  `identity(cfg)`, `make(cfg)`, `make_config_form()` and `make_panels(source)` (each
+  `{id, title, GtkWidget*}`). `make_config_form()` takes no argument: the chooser calls
+  `form.write(cfg)` to fill the form. A `ConfigForm` is a list of `AdwPreferencesRow` widgets
+  plus `write` / `read` / `valid` / `on_change` closures, so the chooser can place the rows in
+  its own group and gate its Connect button on `valid()`.
+- **`SourceRegistry`**: filled by an explicit `register_builtin_sources()` call. No
+  static-init self-registration (linkers can drop it). A future `dlopen` loader would only
+  call `register_kind()`.
+
+### 2. Acquisition and the UDPS plugin
+
+- `Acquisition` takes a `std::unique_ptr<DataSource>` instead of building a `udps_client_t`
+  and implements `SourceSink`; it creates the source lazily in `start()`, from the kind and
+  `SourceConfig` it was given; the four trampolines go away.
+- `on_config` / `on_data` change only in the type they read. Time base, holes, backfill,
+  decimation, trigger and math code are untouched.
+- `run()` calls `source_->poll(50)` and copies `source_->stats()` into
+  `ScopeModel::stats()`. `PacketCapture` stays in `Acquisition`, fed through the datagram
+  tap. Sources without datagrams (E-1608) leave the capture UI disabled, not hidden.
+- `src/source/udps_source.cpp` wraps `deps/udpsclient` unchanged: it maps `udps_signal_t`
+  to `SignalInfo` and `udps_frame_t` to `Frame`, and carries the existing knobs (server,
+  port, multicast, interface, recv buffer). Identity is `host:port`.
+- The `udps_*` types are used only in `acquisition.cpp` today, so no other file changes for
+  this step beyond the `Frame` type.
+
+### 3. UI hosting, config and persistence
+
+- **Connect dialog** (`source_dialog.cpp`): gains a "Source type" dropdown; choosing a kind
+  swaps in that kind's `make_config_form()`. The UDPS form (server, port, multicast,
+  interface) moves into the UDPS plugin. The dialog keeps the known-sources list, buffer
+  size, relative time and capture ring size.
+- **Capability panels**: after the source is created the app calls `make_panels()` and adds
+  each panel as a page of the existing `side_stack` (the side area's page stack, owned by
+  the tab switcher). A panel is insensitive when
+  disconnected (disabled, not hidden; the tab switcher owns visibility). A source with no
+  panels adds no tab; UDPS has none. Panels call `source->post(Command)`, never the source
+  directly, so cross-thread safety lives in one place. A helper kit for common panels (DIO
+  bank, generator form) lives in `src/source/widgets/` but is only added when a plugin uses
+  it, so it arrives with sub-project 3.
+- **Config / CLI**: `Config` gains `source_kind` (default `udps`) and a `SourceConfig`.
+  `--server/--port/--multicast/--interface` populate the UDPS entries. `--source NAME` and
+  repeatable `--source-opt k=v` work for any kind. `--help` lists the registered kinds.
+- **Sessions**: the source's config is stored as top-level TOML keys, `source_kind` and
+  `source_opt_<key>`, written only for non-UDPS kinds (a UDPS session file is unchanged, so
+  legacy `host_port.toml` files read as `udps` with nothing migrated). It is not a `[source]`
+  table. A non-UDPS session file is named by a pseudo-host `<kind>-<identity>` with port 1.
+- **Mocks**: `tools/mock_udpstreamer.py` remains the UDPS mock. Each later plugin ships its
+  own mock under `tools/` so the headless self-check keeps working.
+
+## Verification
+
+- This is a pure refactor for UDPS: the existing headless self-check must read exactly as on
+  `main` -- exactly three build warnings, no `Gtk-CRITICAL` (see `docs/claude/verification.md`).
+- New probe `UDPSCOPE_PROBE_SOURCE_KINDS` (`UDPSCOPE_PROBE_SOURCES` is already the chooser
+  discovery probe). Its value is a delay in ms, and its presence also registers the stub
+  `probe` kind. It extends the probe/dump in `src/ui.cpp` rather than
+  adding a harness. It checks that the registry lists its kinds, that a config form
+  round-trips its `SourceConfig`, and -- with a stub test-only kind carrying one panel --
+  that the panel's tab is built, insensitive while disconnected, and that a posted command is
+  drained by `poll()`.
+- Document the new probe lines in `docs/claude/probe-readings.md`; update `architecture.md`
+  (a `DataSource` replaces the client in the thread description), `build-and-run.md`
+  (new CLI options) and `README.md`.
+
+## Out of scope
+
+- Runtime `.so` loading, and a per-source I/O thread.
+- Multi-timebase data path (sub-project 4).
+- The flat UDP, E-1608 and ABScope plugins (sub-projects 2-4).
+- The DIO / generator helper widgets (arrive with sub-project 3).

docs/superpowers/specs/2026-11-02-e1608-network-scan-design.md

@@ -0,0 +1,63 @@
+# E-1608 network scan -- design
+
+Date: 2026-11-02. Status: approved in conversation, awaiting written-spec review.
+
+## Goal
+
+The E-1608 connection form gets a "Scan network" row that finds boards and fills the address or the
+MAC from a click. Today a user must already know the address, or give a MAC and rely on a lookup.
+
+## Finding (tested on a real board, 2026-11-02)
+
+The board was at 169.254.88.75 on `net0`; the default route is `wlan0`. A `D` probe sent to
+255.255.255.255 with no binding found nothing (it left through `wlan0`). The same probe sent with
+`SO_BINDTODEVICE net0`, or bound to the interface address, or sent to a directed broadcast, or by
+unicast, was answered (64 bytes, first byte `D`). So a single limited broadcast is not enough on a
+host with several interfaces; the existing "find by MAC" lookup has the same flaw.
+
+## Discovery layer (`e1608_link.{hpp,cpp}`)
+
+- `class Scan` (non-blocking, one instance per scan): `Scan(port)` enumerates up, non-loopback IPv4
+  interfaces with `IFF_BROADCAST` (`getifaddrs`), opens one UDP socket per interface bound to it
+  (`SO_BINDTODEVICE`, falling back to binding the interface address if the call is refused), enables
+  `SO_BROADCAST`, and sends `D` to 255.255.255.255 on each. `poll()` drains every socket without
+  blocking and returns the devices found so far (E-1608 product id only, one entry per MAC, the same
+  reply parsing as `discover`). The caller owns the clock.
+- `discover()` keeps its signature. A new overload or helper `discover_broadcast(port, wait_ms)` is
+  `Scan` plus a blocking wait. `E1608Source`'s lookup uses it when the subnet is empty; a given
+  subnet still uses `sweep_targets` + `discover` as today.
+- An interface that cannot be opened or sent on is skipped, never an error; no interfaces is an empty
+  result.
+
+## Form (`e1608_kind.cpp`)
+
+- At the top of the Connection expander, an `AdwActionRow` "Scan network" with a text suffix button
+  "Scan" (widget name `e1608-scan`). The row subtitle reads "Scanning...", "N boards found" or
+  "No board found". No theme icons.
+- A scan starts a `Scan` on the port in the Port field and a 50 ms `g_timeout_add` poll for about
+  1.5 s. There is no thread: the project has exactly two. The timer is removed when the form is
+  destroyed (`Form::alive` guard plus the destroy hook) and when a new scan starts.
+- Each device found becomes an `AdwActionRow` in the Connection expander right after the scan row,
+  replacing the previous results. Title: IP. Subtitle: MAC. Activating the row fills Address and
+  clears MAC and Subnet. A suffix text button "Use MAC" (`e1608-use-mac`) fills MAC and clears
+  Address and Subnet. Fill is done under the form's `updating` guard, then `changed` fires once.
+- Result rows are not read or written by the session: only the filled fields persist.
+- The description line mentions the scan.
+
+## Verification
+
+- A scan probe (env var in the existing pattern): starts against `tools/mock_e1608.py` on a
+  loopback-reachable port, presses the scan button, and prints `[e1608] scan: found=N ip=... mac=...
+  fill_addr=1 fill_mac=1 ok=1`, covering both fills and that the results are replaced on a rescan.
+  If the sandbox refuses the broadcast, the line says so and the limitation is documented, not claimed.
+- A manual run of the scan against the real board, recorded in the README.
+- Baselines unchanged: 3 warnings clean, `gtk warnings: 0`, no `Gtk-CRITICAL`.
+
+## Docs
+
+`README.md` (E-1608 paragraph), `docs/claude/{build-and-run,verification,probe-readings,architecture}.md`.
+
+## Out of scope
+
+Remembering scan results across runs; scanning other subnets than the host's interfaces (the
+`subnet` sweep field remains for that); a worker thread.

docs/superpowers/specs/2026-11-02-flat-udp-source-design.md

@@ -0,0 +1,147 @@
+# Flat UDP source plugin (sub-project 2 of 4)
+
+Date: 2026-11-02
+Branch: to be cut from `feature/source-plugins`
+
+## Context
+
+Sub-project 1 added the `DataSource` / `SourceKind` / `SourceRegistry` framework. Sub-project 3
+added the E-1608. This sub-project adds `flatudp`: a receiver for the MARTe2 `UDPSender`
+datasource (`MARTe2-components/Source/Components/DataSources/UDP/UDPSender.{h,cpp}`).
+
+## The wire format
+
+Read from `UDPSender::Synchronise()` and `MemoryDataSourceI`:
+
+- One `Write` of the datasource memory per `Synchronise()`: **one datagram is one cycle**.
+- The memory is the signals concatenated in declaration order, **no padding**, in the sender's
+  native byte order. `signalOffsets[s]` is the running sum of `size * elements`.
+- There is no header, counter, timestamp or signal description. In IndependentThread mode the
+  first signal is a `uint8` `Trigger`; it is sent like any other signal.
+- The user must therefore enter the exact signal list by hand.
+
+## Decisions
+
+| Question | Decision |
+| --- | --- |
+| Time base | The user declares the nominal cycle rate in Hz (`rate`, required). The existing pipeline stamps the frames: anchored at arrival, samples spaced by the declared cadence, corrected to the measured cadence when the arrivals are more than 25% off it; `--relative-time` gives a purely counted clock. There is no `time_mode` switch: `acquisition.cpp` has no stamping path that ignores the declared cadence, and `sampling_rate = 0` would size the ring and the ingest decimation for 1 kHz (`model.cpp:60`). Loss is never reported (`lost = 0`). |
+| Signal list entry | A row editor: name entry, type dropdown, element count and a remove button per row, plus an "Add signal" row. |
+| Network | Port and optional bind address, plus an optional multicast group and interface. No source-address filter. |
+| Byte order | `little` (default) or `big`. |
+| Out of scope | Auto-detecting the list, importing a MARTe2 `.cfg`, a source filter, loss detection. |
+
+## Config keys
+
+Persisted in the session, settable with `--source-opt`. Kind id: `flatudp`.
+
+| Key | Default | Meaning |
+| --- | --- | --- |
+| `port` | 44488 | UDP port to listen on (the sender's own default). |
+| `bind` | empty | Local address to bind; empty is any. |
+| `multicast` | empty | Group to join; empty is plain unicast. |
+| `iface` | empty | Local interface address for the join. |
+| `rate` | none | Nominal cycle rate in Hz. Required; sizes the ring and the decimation and spaces samples within a frame. |
+| `endian` | `little` | `little` or `big`. |
+| `signals` | none | `name:type[count],...`, e.g. `Trigger:uint8,Ia:float32,Wave:float32[16]`. A persistence format only: the form builds and parses it. |
+
+Types: `uint8/16/32/64`, `int8/16/32/64`, `float32`, `float64`. Count 1 is a scalar signal; N
+is a vector signal. Expected datagram size is the sum of `size * count` over the rows.
+
+Validity (form and `--source-opt` alike): at least one signal; names non-empty and unique;
+count 1-4096; total size at most 65507 bytes; `rate` finite and positive.
+
+## Architecture
+
+New files under `src/source/flatudp/`:
+
+- `flatudp_signals.{hpp,cpp}` -- the `signals` string codec: parse, format, validate, size
+  arithmetic. No GTK, so a probe can round-trip it.
+- `flatudp_source.{hpp,cpp}` -- the `DataSource`.
+- `flatudp_kind.{hpp,cpp}` -- the `SourceKind`, the form, and the registration in
+  `register_builtin_sources()`.
+
+Threading is unchanged: the source lives on the producer thread and `poll()` does all the work.
+
+### Data flow
+
+`poll(timeout_ms)` waits on a non-blocking UDP socket and drains it.
+
+- A datagram of exactly the expected size is decoded row by row to doubles (byte-swapped when
+  `endian=big`).
+- **Batching.** When every row is scalar, decoded datagrams are queued and delivered
+  `block` at a time in one `Frame` (`num_samples = block`), where
+  `block = clamp(round(rate / 100), 1, 1024)`, about 100 frames per second as the E-1608 does. A
+  partial block is flushed after 100 ms so a slow or stopped sender does not hold samples back.
+  When any row is a vector, a vector signal carries one sample per `Frame`, so each datagram is
+  its own frame (`num_samples = 1`).
+- `Frame`: `counter` a running frame count, `lost = 0`, `late = false`, `recv_time` the arrival
+  clock at delivery.
+- `set_datagram_tap` is honoured for every datagram, valid or not, and `has_datagrams()` is
+  true, so packet capture works.
+- `on_config` is called from the first `poll()` with one `SignalInfo` per row (`rows = count`,
+  `cols = 1`, `time_mode = kTimePacket`, `sampling_rate = rate`).
+
+### Errors and state
+
+- A wrong-size datagram is dropped, never decoded. Each distinct size raises one `Error`
+  event ("datagram of N bytes, expected M, check the signal list") and increments `stale`.
+- `Connected` is raised on the first valid datagram and `Disconnected` after 2 s of silence; a
+  later datagram raises `Connected` again.
+- A bind or multicast-join failure raises an `Error` and the source stays disconnected.
+
+### Connect form
+
+Built from `AdwPreferencesRow`s, with the destroy-notify guard used by the E-1608 form.
+
+- Network group: port, bind, multicast, interface.
+- Timing: a rate spin.
+- Byte order combo.
+- Signals group: one row per signal, "Add signal" at the bottom, and a live subtitle with the
+  implied size ("41 bytes per datagram"). `valid()` is false while the list breaks a validity
+  rule.
+- The `signals` string is rebuilt from the rows on every change; `write()` parses it back.
+
+## Verification
+
+No unit suite; the self-check is the contract.
+
+- `tools/mock_flatudp.py`: emits packed structs for a given signal spec and rate; options for
+  big-endian and for one wrong-size datagram.
+- `UDPSCOPE_PROBE_FLATUDP` in `src/ui_probe.cpp`: stream names and count; a hand-computed
+  decode of known values including a vector signal and a `uint64`; the declared rate reaching the model; the
+  wrong-size error reported once and counted in `stale`; disconnect after silence; the form's
+  validity rules; the `signals` codec round trip. A multicast loopback check runs if the
+  sandbox allows it.
+- Baselines unchanged: exactly 3 build warnings, `gtk warnings: 0`, no `Gtk-CRITICAL`.
+
+## Documentation
+
+README (the kind and its limits: no loss detection, the signal list is the user's
+responsibility), `docs/claude/build-and-run.md` (options and mock usage),
+`docs/claude/architecture.md` (source plugins), `docs/claude/probe-readings.md` and
+`docs/claude/verification.md` (the new probe lines).
+
+## Amendment 2026-11-02: how a vector signal is shown (decided with the user during Task 2)
+
+Task 2 found that treating every vector row as one channel of `count` consecutive samples zero-pads
+the scalar channels of a mixed list (the model spans a frame by its largest element block, and
+`Frame::value` is 0 past a scalar's one value) and declares the wrong rate for the vector channel.
+Both readings of a vector are useful depending on the sender, so each vector row picks one:
+
+- **`channels` (default).** `Wave:float32[16]` becomes 16 scalar channels named `Wave[0]` .. `Wave[15]`,
+  one sample per cycle each. All such lists are batched like an all-scalar list.
+- **`waveform`.** `Wave:float32[16]w` is ONE channel receiving a block of `count` consecutive samples per
+  cycle: `SignalInfo{rows=count, cols=1, sampling_rate=rate*count}`, one datagram per `Frame`
+  (`num_samples = 1`).
+
+Rules:
+- The `signals` string takes an optional trailing `w` after the count; `format` emits it only for a waveform row.
+- A waveform row needs `count > 1`.
+- A list with a waveform row must contain only waveform rows, all with the same `count`; otherwise it is
+  invalid, with a message the form shows. (No zero-padding, no holding scalars across a block.)
+- The channel total is capped at 256: scalars count 1, a `channels` row counts `count`, a waveform row counts 1.
+  Over the cap is invalid.
+- `block` batching applies whenever the list has no waveform row; with a waveform row it is 1.
+- The form shows a "Vector as" dropdown (`Channels` / `Waveform`) on rows whose count is above 1, and
+  the channel total in the subtitle.
+- The earlier "Data flow" text saying every vector row forces `num_samples = 1` applies to waveform rows only.

docs/superpowers/specs/2026-11-02-ui-badges-dock-design.md

@@ -0,0 +1,175 @@
+# Badge bar, readouts dock and slide-over panel -- design
+
+Date: 2026-11-02. Status: approved in conversation, awaiting written-spec review.
+
+## Goal
+
+Replace the sidebar's tab switcher and the separate events pane with a layout built the way bench
+scopes build theirs: setup is reached by *the object it configures* (a badge under the plot), results
+are always on screen (a compact dock), and anything bigger than a readout opens in one slide-over
+panel. The sidebar tabs and the left events pane go away.
+
+## Why (the problems, as found in the code)
+
+- **Unreadable tab titles.** `side_view` is pinned at 320 px (`min-sidebar-width` = `max-sidebar-width`
+  in `main-window.ui`), so four text tabs ("Measure / Signals / Analog out / Digital I/O") ellipsize,
+  and a source can add more.
+- **Hard to find things.** The Signals tab stacks a trigger form of up to 15 rows (plus two
+  expanders) on top of the signal list. Cursors and measurements are in Measure, source controls are
+  in their own tabs, the header is icon-only, and the trigger/cursor toggles live apart from their
+  panels.
+- **The events pane is a different application.** A `GtkPaned` + `GtkRevealer` on the left with its
+  own bold title and header, a dragged width that is not saved, thumbnails the rest of the UI does
+  not have, and a header toggle that is hidden until events exist.
+
+## State of the art this follows
+
+- Tektronix 5/6 Series: a badge bar under the waveform (a badge per channel/math waveform, plus
+  Horizontal, Trigger, Acquisition badges); a tap opens *only that item's* settings; results
+  (measurements, cursors, search) are a separate bar that does not cover the waveform.
+- Scopy and PicoScope 7: a channel list at the edge and a settings panel that slides in for the
+  selected item (PicoScope lets it overlay or squeeze the trace).
+- Saleae Logic 2: one side panel at a time; decoded results also in a list beside the waveform.
+- Keysight InfiniiVision: dialogs that can be undocked so cursor and measurement values show together.
+
+## Layout
+
+```
+┌ header: [window 2 s ▾] [Trigger] [Pause] [Cursors]        [Dock] [☰] ┐
+├──────────────────────────────────────────────┬────────────────────┤
+│  plot rows                      ┌───────────┐ │ READOUTS           │
+│                                 │ slide-over│ │  cursors, measures │
+│                                 │ settings  │ ├────────────────────┤
+│                                 └───────────┘ │ EVENTS (n)         │
+├───────────────────────────────────────────────┴────────────────────┤
+│ [●sine][●square][+]  …                        [Trigger ▸][Source ▸]│
+├ status line ───────────────────────────────────────────────────────┤
+```
+
+### Header bar
+
+Keeps the time-window control, the Trigger, Pause and Cursors toggles and the overflow menu. The
+Events toggle is removed (Events is always in the dock). The sidebar toggle becomes the **Dock**
+toggle, so a narrow window can still hide the dock. There is no "Window" badge: the header's control
+is the timebase, and a second one would duplicate it.
+
+### Right dock ("Readouts" and "Events")
+
+- Fixed width, about 280 px; always on screen, shown but insensitive until the stream has signals
+  ("disable, do not hide"). It stays an `AdwOverlaySplitView` sidebar, which already gives it its
+  own fixed width, the hide toggle and the overlay behaviour on a narrow window
+  (`invariants-plot-and-layout.md`).
+- **Readouts** (top): the active cursor values and measurement values, read-only, one compact line per
+  value, through the one formatter both panes share (`invariants-readouts-and-cursors.md`).
+  An "Edit" affordance opens the slide-over's `measure` or `cursors` page; clicking a measurement row
+  opens that measurement's editor.
+- **Events** (bottom): compact rows -- title, time, a small marker; no thumbnails. Insensitive outside
+  trigger mode. A "Manage" affordance opens the slide-over's `events` page.
+
+### Badge bar
+
+A fixed-height row between the plot and the status line.
+
+- **Signals** (left): one badge per enabled signal, up to 6; beyond that a single "N signals" badge.
+  A badge shows a colour dot and the name, is a drag handle (reorder, or drop on a plot row, which
+  replaces today's drag from the signal list), and opens that signal's page (colour, calibration,
+  row, math). A trailing `+` opens the `signals` page (the full list, to enable more; the math editor
+  entry).
+- **System** (right): **Trigger** shows its state (off / armed / triggered) and opens the trigger
+  form; **Source** shows the connection state and the source name and opens that source's pages
+  (`SourcePanel` pages, behind a small segmented switch inside the panel when there are several, as
+  E-1608 has Analog out and Digital I/O).
+
+### Slide-over panel
+
+- Overlays the plot's right edge (about 360 px wide), never the dock; one page at a time; Esc or a
+  click outside closes it. The plot is not resized by it.
+- Pages, by id: `trigger`, `signal:<name>`, `signals`, `measure`, `cursors`, `events`,
+  `source-<id>`. Each page has its own scroller, so a tall page does not leave a shorter one scrolled
+  (the reason the sidebar had a scroller per page).
+- Content: the trigger form (conditional rows, Advanced, Search the buffer), signal and calibration
+  settings, measurement add/edit/remove and statistics, cursor options, event actions (Live, Compare,
+  Accumulate), the math editor entry, and source pages.
+
+### Status line
+
+Unchanged.
+
+## Components
+
+New files, because `ui.cpp` is already very large.
+
+| Unit | File | Responsibility |
+| --- | --- | --- |
+| `BadgeBar` | `ui_badges.cpp` | Builds signal / Trigger / Source badges from the model; emits "open page X"; owns badge drag. |
+| `SlideOver` | `ui_slideover.cpp` | A `GtkOverlay` child of the plot area: revealer + page stack keyed by id; Esc/click-away; open/close API. |
+| `ReadoutsDock` | `ui_dock.cpp` | The compact readouts and the compact events list, reading the same model the panes read today. |
+
+Reuse, not rewrite:
+
+- The trigger form, signal list and calibration, measurement editor and cursor options are
+  **reparented** into slide-over pages.
+- `SourcePanel{id, title, widget}` is unchanged, so the E-1608 and Flat UDP panels need no change.
+- Only the events *list and actions* of the old pane move; the left `GtkPaned`/`GtkRevealer` and its
+  divider sync are deleted.
+
+## Invariants kept
+
+- **Layout must not depend on content** (`invariants-plot-and-layout.md`): the dock has a fixed width,
+  the badge bar a fixed height, and the slide-over overlays instead of resizing the plot. Rows that
+  appear by trigger condition appear inside the slide-over's scroller.
+- **A `GtkOverlay` child is picked wherever its allocation is**: the slide-over is one opaque widget
+  aligned to the end edge by margin and width, never a full-area transparent child, so pan, drop and
+  hover on the rest of the plot are untouched.
+- The header's Trigger/Cursors/Pause toggles keep their two-way mirroring with the panels.
+
+## State and session file
+
+- The session file drops `side_tab` and gains the dock's shown state and width. An old file's
+  `side_tab` is ignored (an unknown name is already harmless to `select_side_tab`).
+- The open slide-over page is not saved.
+- The tab ids `measure`, `signals` and `source-<id>` stop being a session format; they remain page ids.
+
+## What must be rewritten around it
+
+- **Tour and context help:** steps and help-figure surfaces that point at `side_switcher`,
+  `side_stack` and `side_box` (`ui_tour.cpp`, `ui_context_help.cpp`) are re-pointed at the badge bar,
+  slide-over and dock, and the tour text is rewritten.
+- **Probes:** the `switcher: policy=... pills=... labels=... images=... pages=...` line and
+  `side_tab_probe` become probes that count badges, dock rows and the open slide-over page; the events
+  divider probe goes away with the divider.
+- **Keyboard:** `SideTabMeasure` / `SideTabSignals` become "open the measure / signals page".
+- **Docs:** `README.md`, `USER-GUIDE.md`, `docs/claude/*` (architecture, verification,
+  probe-readings, the plot-and-layout and gtk-and-chrome invariants), and the Mallard manual's
+  figures.
+
+## Rollout
+
+Four steps, each its own plan, each leaving the app building, passing the probes and usable.
+
+1. **Shell.** The plot overlay, the badge bar with Trigger and Source, the slide-over holding the
+   existing trigger form and source pages. The sidebar tabs are removed; the existing Measure and
+   Signals panels move into a temporary dock so nothing is lost.
+2. **Signal badges.** Per-signal badges, the `+` and "N signals" overflow, drag to reorder and to
+   move to a row.
+3. **Compact readouts.** Read-only cursors and measurements in the dock; their editors in the
+   slide-over.
+4. **Events.** The compact events section in the dock, the left pane and divider deleted, then the
+   tour / help / docs sweep.
+
+## Risks
+
+- **Overlay above the GL plot.** The panel must composite and take input correctly above the
+  plotter's GL area. The layout editor already places overlay children over the plot, so this is
+  expected to work; step 1 confirms it before anything else is built on it.
+- **Reparenting the trigger form.** Its two-way mirroring with the header toggle, `sync_trigger_rows`
+  and the locked summary view must keep working from a hidden-by-default page. Step 1 verifies it with
+  the existing trigger probes.
+- **Many signals.** The badge bar's six-badge limit and horizontal behaviour are the one place the
+  E-1608 (up to about 17 signals) stresses the design; step 2 includes a run on it.
+
+## Out of scope
+
+User-arranged or undockable panels, saved layouts of the panels themselves, a touch-specific mode,
+and any change to the plot, trigger, measurement or source engines. Per-source tab names do not
+change.

docs/superpowers/specs/2026-11-03-horizontal-split-design.md

@@ -0,0 +1,92 @@
+# Horizontal plot split -- design
+
+## Goal
+
+Let each row of the stacked plots be split into several plots side by side. All plots share one
+time window (one x link, one zoom/pan, one crosshair). A split only arranges more plots on screen; it
+is not an independent time window and not an XY plot.
+
+## Decisions
+
+1. **Shared time window.** Cells in a row, and rows in the figure, are all members of the one x link
+   group. No new time semantics.
+2. **Per-row split.** Each figure row holds 1..4 cells, independently of the other rows.
+3. **Draggable cell widths**, saved with the session, mirroring row heights (`weight`).
+4. **Caps.** At most 4 cells per row and at most 8 plots in total (`RowSet::kMaxRows` keeps its value
+   and now bounds plots, not figure rows). Every per-plot structure sized for 8 stays as is.
+5. **Approach.** Extend the vendored plotter's `Figure` so a figure row holds several plots; the host
+   treats each cell as one plot. Rejected: several `Figure`/`PlotArea`s linked by hand (cannot express a
+   per-row split, reintroduces manual x/crosshair sync) and a general tiling tree (not asked for).
+
+## Plotter (`deps/plotter`)
+
+- `Figure` is constructed from cells-per-row (e.g. `{1,2,1}`). `Figure(u32 rows)` stays and means one
+  cell per row, so existing behaviour and `tests/test_figure.cpp` are unchanged.
+- `plot(i)` indexes the flattened cells, top to bottom, left to right. `sync_x_links()` and the
+  crosshair already work on any set of plots and need no change.
+- New: `set_cell_weights(row, weights)` and `set_col_gap(px)`. Widths use the height scheme: a floor
+  per cell, the weights share the rest, the last cell closes the row exactly (no seam).
+- `FigureLayout` gains `cells` (one `Rect` per plot, flattened). `rows` stays the full-width rect per
+  figure row.
+- Only the bottom figure row's cells carry x labels and the x title; other cells get `XStrip::None`.
+- The left y gutter stays one common maximum for the whole figure with the same reserved floor. A
+  per-column gutter would make cell width depend on content, which the layout rule forbids.
+- A figure too narrow for the floor widths shrinks the cells proportionally and drops the column gap,
+  as heights do; no rect is ever negative.
+- Pointer hit-testing finds the plot under the cursor by its cell rect.
+- The change is documented in `docs/claude/build-and-run.md` with the other vendored changes.
+
+## Host (`src/plot_host.*`, `src/ui_layout.cpp`, `src/layout_store.*`, `src/ui.cpp`)
+
+- Everything keyed by a plot index keeps meaning "flattened plot index": cursors, measurements,
+  `bind()`, readouts, persistence layers, `cursors_pane_bound`.
+- `RowSet` gains `cells_per_row_` and per-figure-row cell weights, re-applied after every rebuild like
+  `row_weights_`. `split_cell(i)` / `remove_cell(i)` change a row's cell count; a removed cell drops its
+  traces, a new cell starts empty. `insert_row` / `remove_row` act on figure rows and carry their cells.
+- `row_count()` stays the plot count; `figure_row_count()` is added. The plan may rename if this reads
+  badly.
+- Cursors: the vertical pair is one shared time drawn in every cell; horizontal rulers are per cell.
+  The crosshair is one x on every cell, the hovered cell shows its y.
+- Y axes are per cell (auto or manual); fit-all fits each; wheel and axis drags act on the cell under
+  the pointer; an x gesture anywhere moves the shared window.
+- A signal dropped on a cell lands in that cell with the same slot rule as a row. The signals page's
+  "place on row" choice lists cells ("row 2, left") only for split rows.
+- Persistence layers fill free slots of the same cell.
+
+## Layout editor
+
+Mirrors the row controls:
+
+- Each vertical boundary between two cells gets a `+` (insert a cell) and a drag arrow (resize the two
+  neighbours). Each row's left and right edge gets a `+`, so a one-cell row can be split from either side.
+- Each cell keeps its top-left `×`: in a multi-cell row it removes the cell; in a one-cell row it
+  removes the row, as today. Insensitive when it would leave no plot.
+- Cell `+` is insensitive at 4 cells in the row or 8 plots in total; the row `+` is insensitive at 8
+  plots in total.
+- A divider drag moves the two neighbouring widths, each floored at about 96 px logical, relative to the
+  weights at drag start (as the row drag is). Saved on drag end.
+- Outside the editor nothing changes except the extra plots.
+
+## Session file
+
+`[[plot]]` tables gain `row` (the figure row) and `width` (the cell's weight). A session without `row`
+loads as one cell per row, so existing sessions open unchanged. Row `weight` stays per figure row (carried
+on the row's first cell).
+
+## Verification
+
+- `tests/test_figure.cpp`: `{1}` identical to today; `{1,2}` tiles exactly; weights and floors respected;
+  a narrow figure degrades without negative rects; x link and crosshair span all cells.
+- New headless probe `UDPSCOPE_PROBE_SPLIT_MS`: split a row, drop a signal in each cell, drag a divider;
+  check the cells tile the width, the shared x range is identical, both vertical cursors line up in every
+  cell, widths survive a session round-trip, and a session without `row` still loads. Expect
+  `gtk warnings: 0`, no `Gtk-CRITICAL`.
+- Regression: layout, cursors, measurements, readouts and E-1608 probes read as before; the baseline file
+  is re-baselined only where this feature explains a difference.
+- Layout dumps and probes that print per-row layout gain a cells list and a column-weights line.
+
+## Docs
+
+`README.md`, `docs/USER-GUIDE.md`, `help/C/org.udpscope.app/` (layout page), `docs/claude/probe-readings.md`,
+`docs/claude/verification.md`, `docs/claude/invariants-plot-and-layout.md` (cell rules),
+`docs/claude/build-and-run.md` (plotter change), and `ui_context_help.cpp` where the layout editor is described.

docs/superpowers/specs/2026-11-03-split-shared-y-design.md

@@ -0,0 +1,80 @@
+# Split rows share one y axis -- design
+
+Amends `2026-11-03-horizontal-split-design.md`. Where the two disagree, this one governs.
+
+## Goal
+
+The cells of a split row share one y range and draw one y axis, the way the rows of the figure share
+one x window and draw one x axis. A split row reads as one wide plot with dividers.
+
+## Decisions
+
+1. **Always shared, no option.** All cells of a figure row have one y range. An unsplit row is
+   unaffected.
+2. **One y axis per row.** Only the leftmost cell has a y gutter and y labels. The other cells have
+   none, as only the bottom row carries x labels.
+3. **Rulers are per row.** The two horizontal rulers (cursor pair) belong to the figure row and are
+   drawn at the same y in every cell. A drag in any cell moves them.
+4. **Approach.** Extend the vendored plotter with a y link, symmetric to the x link. Rejected: syncing
+   the ranges from the host every frame (the plotter's own per-plot autoscale and the controller's
+   gestures would fight it, which is the problem the x link already solves).
+
+## Plotter (`deps/plotter`)
+
+- `Figure::set_share_row_y(bool)`, default off so existing figures and `tests/test_figure.cpp` are
+  unchanged. When on, the cells of each figure row form an implicit y link group. The group is rebuilt
+  with the cells.
+- A y link syncs like the x link: in `layout()` a new `sync_y_links()` adopts a member's changed
+  `y_range` as the group range and pushes it to the other members. Wheel, pan, box zoom and axis drag
+  go through `set_y_range`, so they need no controller change.
+- Auto scale: a member's own autoscale is suppressed (as `Axis::link_member` already blocks `Live`).
+  The group owns the auto flag and fits to the union of its members' visible traces; cells with no
+  trace are ignored; a log axis takes the union in axis space. `fit_all` and double-click fit the
+  group, not one cell. A manual `set_y_range` on a member clears the group's auto flag.
+- `YStrip {Both, None}` and `Plot::set_y_strip_mode`, mirroring `XStrip`. `None` forces the y label
+  width, title width and reserved floor to 0. `Figure::layout` sets `None` on every cell but the
+  first of its row, structurally from the column index, never from content. `None` cells are skipped
+  in the common-gutter maximum.
+- Cell widths: the row's y gutter is taken off the row width first, then the cells share the rest by
+  the existing `floor + extra*w/total` rule. Equal weights therefore give equal plot areas; the first
+  cell's rect is gutter plus its plot width, and the cell rects still tile the row exactly. The
+  floors apply to plot widths.
+- A y axis-drag can only start in the leftmost cell (the others have no label area).
+- Documented in `docs/claude/build-and-run.md` with the other vendored changes.
+
+## Host (`src/plot_host.*`, `src/ui*.cpp`)
+
+- `set_y_auto`, `set_y_range`, `fit_all`, and the Auto/Fixed dialog act on the figure row of the plot
+  they are given. The dialog reads the row's range.
+- Rulers: one pair per figure row, stored on the row's first plot index and placed in every cell by
+  `place_cursors`; `sync_cursors` reads the dragged one back; `reset_cursors` and the measure level
+  marks use the row's range. The cursors pane lists the pair once per figure row.
+- `row_unit` joins the units over all cells of the row, "" if mixed.
+- `sync_compare_axes` is unchanged: it writes x and y once per `RowSet` row. The comparison panes are flat single-cell rows, so that is once per figure row and no y sharing is involved.
+- `rebuild_all` turns the sharing on for the new `Figure` before the cells are populated.
+- Readouts and measurements stay per trace and per plot index; only the axis is shared.
+- Session file: unchanged (y ranges were never persisted).
+
+## Layout editor
+
+Divider drag maps the pointer to weights through plot widths, not cell widths: for the first cell,
+subtract the row's gutter from the left rect before applying `frac = (want_left-64)/(pair-128)`. The
+96 px logical floor applies to the plot area. Nothing else changes.
+
+## Verification
+
+- `tests/test_figure.cpp`: with sharing on, a `{2}` row has equal y ranges after a `set_y_range` on
+  either cell; a second cell has zero y gutter and the first the common maximum; widths tile exactly and
+  equal weights give equal plot widths; group autoscale covers the union and ignores empty cells; sharing
+  off reproduces today's layout; `{1}` rows unaffected.
+- Split probe gains: after a y gesture on one cell the other's range is identical; non-first cells have
+  no y gutter; fit-all covers both cells' traces; both rulers line up across cells; a divider drag still
+  tracks the pointer within 1 px.
+- Regression: layout, cursors, measurements, readouts, E-1608 probes read as before; re-baseline only
+  what this feature explains. `gtk warnings: 0`, no `Gtk-CRITICAL`.
+
+## Docs
+
+`README.md`, `docs/USER-GUIDE.md`, `help/C/org.udpscope.app/` (layout page), `docs/claude/probe-readings.md`,
+`docs/claude/invariants-plot-and-layout.md` (the "one gutter, not per column" rule and the per-cell y
+rule), `docs/claude/build-and-run.md`, `ui_context_help.cpp`, `CLAUDE.md` if it mentions per-cell y.

help/C/org.udpscope.app/cursors.page

@@ -0,0 +1,90 @@
+<page xmlns="http://projectmallard.org/1.0/"
+      type="topic" style="task"
+      id="cursors">
+
+  <info>
+    <link type="guide" xref="index#analysis"/>
+    <link type="seealso" xref="measurements"/>
+    <desc>The shared vertical cursor pair and the per-row horizontal rulers, their four modes,
+    and how a reading is formatted.</desc>
+    <credit type="author copyright">
+      <name>Martino Ferrari</name>
+    </credit>
+  </info>
+
+  <title>Cursors</title>
+
+  <p>Cursors read values off the traces. There are two kinds: one <em>shared vertical
+  pair</em> that every row carries at the same time, and <em>horizontal rulers</em>, one pair
+  per row, that belong to that row alone.</p>
+
+  <section id="reach">
+    <title>How to reach it</title>
+    <steps>
+      <item>
+        <p>Press the cursors button in the header bar, or <key>c</key>. It switches the cursors on
+        and off.</p>
+      </item>
+      <item>
+        <p>The readings are in the dock (a read-only copy) and on the <gui>Cursors</gui> page, which
+        <gui>Edit</gui> beside <gui>Cursors</gui> opens over the plot and which owns the mode
+        and a <gui>Reset</gui> button. Drag a marker to move it.</p>
+      </item>
+      <item>
+        <p>The mode dropdown offers four modes: <gui>vertical</gui> (the shared time pair),
+        <gui>horizontal</gui> (the per-row rulers), <gui>both</gui>, and <gui>mix</gui>.</p>
+      </item>
+    </steps>
+  </section>
+
+  <section id="knowing">
+    <title>Worth knowing</title>
+    <list>
+      <item><p>The vertical pair is <em>one</em> time for the whole figure, so moving it on
+      any row moves it on all of them. That is what makes <code>dt</code> meaningful across
+      rows.</p></item>
+      <item><p>A ruler belongs to its row and nothing shares it, so two rows' rulers are
+      independent. The plots of a split row are one row here: they share their y axis, so the
+      rulers are at the same values in each.</p></item>
+      <item><p><gui>mix</gui> is the reading mode: one line per <em>bound</em> trace, with the
+      trace's own values at each marker and their difference. A slot with a name but no
+      channel behind it is not a trace and gets no line.</p></item>
+      <item><p>A value is the <em>nearest stored sample's</em>, never a number between two
+      samples. Zoom in past the sample spacing and the line between two samples is something
+      the plot drew, not data — so a reading off it would be the drawing. The hover crosshair
+      reads the same way.</p></item>
+      <item><p>Every reading carries a <em>metric prefix</em> so the digits sit in
+      <code>1..999</code>: <code>10.52 mV</code>, not <code>0.01 V</code>. Two decimals is all
+      an instrument landing on an <code>f32</code> sample can claim, so without the prefix a
+      small value would read <code>0.00</code> and the reading would be gone. A stream that
+      declares no unit gets the prefix anyway, written tight against the number
+      (<code>585.24m</code>) — the space separates the number from its unit, and a spaced
+      <code>m</code> with nothing after it would read as metres.</p></item>
+      <item><p>A marker past the newest sample reads <code>--</code>. With only one marker
+      over data the row reads <code>partial</code>: a difference between a number and nothing
+      is not a number.</p></item>
+      <item><p>In <gui>mix</gui> each marker also places a crossing annotation per trace,
+      which is what lets you see on the plot which sample a number came from. It is <em>on
+      that sample</em>, so when the marker falls between two it sits a little off its own
+      line: the line is where you put the marker, the dot is the datum being quoted. The hover
+      crosshair's mark snaps the same way, and is drawn larger than a trace's sample dots so
+      it does not read as one more sample.</p></item>
+      <item><p>The time row exists only in the modes that show the vertical pair.
+      <gui>horizontal</gui> has no time row, by design.</p></item>
+      <item><p>A cursor <em>stays where you put it</em> while a live view rolls under it,
+      which is what a bench scope does: its <code>T0</code> is an age, so a marker left at
+      <code>-1.5s</code> keeps reading the sample a second and a half old as the stream
+      advances. A measurement's marks do the opposite — they travel with the sample they
+      measured — because a cursor is a question you asked and a mark is an answer about one
+      particular sample.</p></item>
+    </list>
+  </section>
+
+  <section id="example">
+    <title>Example</title>
+    <p>Three traces in <gui>mix</gui> mode with both markers over data: 3 lines and 6 crossing
+    marks, each line reading like <code>sine  0.31 V  -0.84 V  -1.15 V</code>. Move the second
+    marker past the newest sample and the third column reads <code>--</code>.</p>
+  </section>
+
+</page>

help/C/org.udpscope.app/export.page

@@ -0,0 +1,78 @@
+<page xmlns="http://projectmallard.org/1.0/"
+      type="topic" style="task"
+      id="export">
+
+  <info>
+    <link type="guide" xref="index#output"/>
+    <link type="seealso" xref="sessions"/>
+    <desc>Writing the visible range of every plotted trace to NumPy, CSV or MDF 3.30, and what
+    each format carries.</desc>
+    <credit type="author copyright">
+      <name>Martino Ferrari</name>
+    </credit>
+  </info>
+
+  <title>Saving and export</title>
+
+  <p>Export writes the <em>visible range</em> of every plotted trace to a file: NumPy
+  <file>.npy</file>, <file>.csv</file>, or <gui>MDF 3.30</gui> (<file>.mf3</file> or
+  <file>.mdf</file>), chosen by the extension you type.</p>
+
+  <section id="reach">
+    <title>How to reach it</title>
+    <steps>
+      <item>
+        <p>Pick <gui>Export visible range…</gui> in the overflow menu, or press
+        <keyseq><key>Ctrl</key><key>E</key></keyseq>.</p>
+      </item>
+      <item>
+        <p>A file chooser asks where; the format follows the path's extension.</p>
+      </item>
+    </steps>
+  </section>
+
+  <section id="knowing">
+    <title>Worth knowing</title>
+    <list>
+      <item><p>The table is collected at the moment you click, not when the chooser returns. A
+      live view keeps scrolling while a dialog is up, so a late collection would write a window
+      you never saw.</p></item>
+      <item><p>The rows are the <gui>stored samples</gui>, never the LOD buckets the plot draws
+      from. A row count far below the span times the stored rate means something cut the table
+      from the pyramid.</p></item>
+      <item><p>The stored rate is not always the wire rate. A window long enough to need
+      decimation is stored averaged at a lower rate, and the export carries <em>that</em> —
+      read the status bar's ⓘ popover for the figure before trusting a sample count.</p></item>
+      <item><p>Two time columns. <code>time</code> is the display timeline — negative ages
+      ending at 0 while streaming, offsets from the trigger edge while an event is held — so it
+      is the x you read a value at on screen. <code>abs_seconds</code> is the source's own
+      clock for the same sample, which is what lets two exports taken in different modes line
+      up. Both are strictly increasing and evenly spaced; duplicate or backwards stamps would
+      mean the file held two clocks.</p></item>
+      <item><p>An export taken <em>mid-capture</em> writes the partly filled window that is on
+      screen, which is shorter than the event span. Export outside a capture if you want the
+      whole event.</p></item>
+      <item><p><gui>MDF</gui> exists for handing a window to another tool, and its shape follows
+      the contract that reader uses: one channel group, every channel record-interleaved, the
+      master channel as the x axis and the unit in the channel metadata. So there the
+      <em>master is <code>abs_seconds</code></em>, named <code>time</code> — the clock that is
+      the same in every display mode — and the display axis goes out beside it as an ordinary
+      channel, <code>time_relative</code>. Both are seconds; each signal carries the source's
+      own unit. That is also what <gui>ScryLab</gui> reads: channel name → signal name, master
+      → x axis, unit → the signal's unit.</p></item>
+    </list>
+  </section>
+
+  <section id="example">
+    <title>Example</title>
+    <p>A 2 s window at 10 kS/s over 3 traces writes 20001 rows and 5 columns
+    (<code>time</code>, <code>abs_seconds</code>, three signals). The <file>.npy</file> is
+    <code>64·⌈(10+len(header)+1)/64⌉ + rows·(16 + 4·cols)</code> bytes. Read it back with
+    <code>pd.DataFrame(np.load(path))</code>. The <file>.mf3</file> is bigger — a block per
+    channel plus a comment — <code>272 + comment + rows·record + 28 + channels·274 + 30</code>
+    bytes, with <code>record = 16 + 4·cols</code> and <code>channels = cols + 2</code> for the
+    master and the relative axis. Read that one back with <code>asammdf.MDF(path)</code> or in
+    ScryLab.</p>
+  </section>
+
+</page>

help/C/org.udpscope.app/index.page

@@ -0,0 +1,67 @@
+<page xmlns="http://projectmallard.org/1.0/"
+      type="guide" style="task"
+      id="index">
+
+  <info>
+    <desc>udpscope plots a live UDPStreamer source as one figure of up to eight stacked
+    plot rows sharing a single time axis, with a trigger, cursors, measurements, math
+    channels and an export. This manual covers connecting, the window and its panels,
+    navigating and pausing the plot, the trigger and its event cache, analysis, and
+    saving and exporting.</desc>
+  </info>
+
+  <title>udpscope</title>
+
+  <section id="main">
+    <title>Getting started</title>
+    <list>
+      <item><p><link xref="overview">Overview</link> — what udpscope is, how it reaches a
+      source, the window and its panels, and a first five minutes.</p></item>
+      <item><p><link xref="source">Choosing a source</link> — the command line, the
+      chooser, and opening an exported waveform instead of a live stream.</p></item>
+      <item><p><link xref="signals">Signals and calibration</link> — how a signal becomes
+      a channel, what starts acquisition, and how a scale and offset are applied.</p></item>
+      <item><p><link xref="layout">Rows, layout and drag &amp; drop</link> — up to eight
+      rows, four traces each, and the layout editor.</p></item>
+    </list>
+  </section>
+
+  <section id="viewing">
+    <title>Viewing</title>
+    <list>
+      <item><p><link xref="window">Time window</link> — the one control that changes the
+      window, and the decimation a long window causes.</p></item>
+      <item><p><link xref="navigate">Navigating the plot</link> — panning, zooming and
+      fitting with the mouse and the keyboard.</p></item>
+      <item><p><link xref="pause">Pause and play</link> — freezing the display without
+      stopping the stream, and how long you have been looking.</p></item>
+      <item><p><link xref="trigger">Trigger</link> — the four trigger shapes, arming,
+      hold-off, the event cache, and searching the buffer.</p></item>
+    </list>
+  </section>
+
+  <section id="analysis">
+    <title>Analysis</title>
+    <list>
+      <item><p><link xref="cursors">Cursors</link> — the shared vertical pair and the
+      per-row horizontal rulers.</p></item>
+      <item><p><link xref="measurements">Measurements</link> — a statistic of the visible
+      window, its on-plot marks, and its statistics line.</p></item>
+      <item><p><link xref="math">Math channels</link> — building a derived channel from a
+      graph of source nodes, operations and one output.</p></item>
+    </list>
+  </section>
+
+  <section id="output">
+    <title>Output and state</title>
+    <list>
+      <item><p><link xref="export">Saving and export</link> — the visible range to
+      <file>.npy</file>, <file>.csv</file> or <file>.mf3</file>.</p></item>
+      <item><p><link xref="sessions">Sessions and settings</link> — the per-source
+      configuration files and what they carry.</p></item>
+      <item><p><link xref="status">Status bar and diagnostics</link> — the glance line, the
+      ⓘ popover, and the activity badge.</p></item>
+    </list>
+  </section>
+
+</page>

help/C/org.udpscope.app/layout.page

@@ -0,0 +1,99 @@
+<page xmlns="http://projectmallard.org/1.0/"
+      type="topic" style="task"
+      id="layout">
+
+  <info>
+    <link type="guide" xref="index#main"/>
+    <link type="seealso" xref="signals"/>
+    <desc>How the figure's rows, plots and traces are arranged, how to drop a signal onto a plot, and
+    how the layout editor adds and removes rows and splits a row into plots side by side.</desc>
+    <credit type="author copyright">
+      <name>Martino Ferrari</name>
+    </credit>
+  </info>
+
+  <title>Rows, layout and drag &amp; drop</title>
+
+  <p>The figure is a stack of rows holding 1 to 8 plots in all, and a row can be split into up
+  to 4 plots side by side. Each plot holds up to 4 traces. Every plot shares one time axis and
+  the figure has one pair of side margins, so the y labels line up, the data areas start and
+  end on the same two columns, and the windows cannot drift apart. The left
+  margin holds the y labels; the right one is empty, and is there so the newest tick's label
+  and the newest sample's ink have somewhere to land instead of sitting on the frame.</p>
+
+  <section id="reach">
+    <title>How to reach it</title>
+    <steps>
+      <item>
+        <p>Drag a signal's badge from the badge bar onto a row to
+        add a trace.</p>
+      </item>
+      <item>
+        <p>Press <key>l</key>, or pick <gui>Layout editor</gui> from the overflow menu, to add
+        and remove rows: a <gui>×</gui> appears at the top left of each plot and a <gui>+</gui>
+        on each boundary between rows, including above the first and below the last.</p>
+      </item>
+      <item>
+        <p>The editor's own button in the top-right corner leaves it.</p>
+      </item>
+    </steps>
+  </section>
+
+  <section id="split">
+    <title>Splitting a row</title>
+    <steps>
+      <item>
+        <p>In the layout editor, click the <gui>+</gui> at a row's left or right edge, or the
+        <gui>+</gui> between two plots, to add a plot to that row. The new plot starts empty.</p>
+      </item>
+      <item>
+        <p>Drag the double-headed arrow on the boundary between two plots to resize them. Neither plot can be
+        made narrower than about 96 px, and the widths are saved with the session.</p>
+      </item>
+      <item>
+        <p>Click the <gui>×</gui> of a plot in a split row to remove that plot and its traces.
+        In a row with a single plot the <gui>×</gui> removes the row instead.</p>
+      </item>
+    </steps>
+    <p>All the plots of a row, and of the whole figure, share one time window: zooming or
+    panning along time in any of them moves all of them, and the vertical cursors are drawn in
+    every plot. The plots of a split row also share one y range: the y labels are drawn at the
+    left of the first plot only, the horizontal cursors sit at the same values in every plot, and a
+    zoom, pan, fit or fixed range in any of them applies to the whole row. The time labels
+    sit under the bottom row, and under any row above it whose columns differ from the row below. A row holds at most 4 plots and the figure at most 8
+    in total; the <gui>+</gui> buttons go grey at the limit.</p>
+  </section>
+
+  <section id="knowing">
+    <title>Worth knowing</title>
+    <list>
+      <item><p>A plot's own <gui>right-click menu</gui> (the same compact rows as the app's
+      menu) holds the y-axis scale (for the whole row), the two fits, and <gui>Remove signal</gui>, which swaps
+      the menu to that plot's traces plus <gui>All traces on this plot</gui> — with a
+      <gui>Back</gui> row to return. That is how a trace comes off a row without going through
+      the layout editor.</p></item>
+      <item><p>A drop <em>adds</em> a trace to the row's next free slot; it does not replace
+      one. With four traces already on a plot the drop is refused.</p></item>
+      <item><p>Inserting a row moves the rows below it <em>with their contents</em>, split
+      rows included. Inserting above row 1 puts what row 1 plotted onto row 2 and leaves the
+      new row empty — the rows are not renumbered under you. A split row's plots are named
+      <em>2a</em>, <em>2b</em> and so on.</p></item>
+      <item><p>A trace is remembered by the signal's <em>name</em>, not by its channel number,
+      because a new CONFIG or an enable renumbers the channels and an index would silently
+      re-point the trace.</p></item>
+      <item><p>Adding or removing a row rebuilds the figure, which is cheap, but it also
+      re-deals every trace. A frozen trigger event survives the rebuild: the pinned window is
+      restated rather than re-framed on the live edge.</p></item>
+    </list>
+  </section>
+
+  <section id="example">
+    <title>Example</title>
+    <p>With three traces on row 1, pressing <key>l</key> shows 7 buttons: the <gui>×</gui>,
+    the two <gui>+</gui> above and below the row with their two resize arrows, and the two
+    <gui>+</gui> at the row's left and right edges. Clicking the <gui>+</gui> above row 1 gives 2 rows and 12 buttons,
+    with the three traces now on row 2 — the layout probe reports exactly this as
+    <code>rows=2 buttons=12 traces=[0:-|1:sine,ramp,noise]</code>.</p>
+  </section>
+
+</page>

help/C/org.udpscope.app/math.page

@@ -0,0 +1,112 @@
+<page xmlns="http://projectmallard.org/1.0/"
+      type="topic" style="task"
+      id="math">
+
+  <info>
+    <link type="guide" xref="index#analysis"/>
+    <link type="seealso" xref="signals"/>
+    <desc>Building a derived channel from a graph of source nodes, operations and one output,
+    and how the graph is evaluated.</desc>
+    <credit type="author copyright">
+      <name>Martino Ferrari</name>
+    </credit>
+  </info>
+
+  <title>Math channels</title>
+
+  <p>A math channel is a signal computed from other signals. You build it as a small graph —
+  source nodes, operations, one output — and udpscope then treats the result as an ordinary
+  channel.</p>
+
+  <section id="reach">
+    <title>How to reach it</title>
+    <steps>
+      <item>
+        <p>Open the <gui>Signals</gui> page (the <gui>+</gui> badge, or <key>g</key>). Math channels
+        are listed under a <gui>MATH</gui> heading.</p>
+      </item>
+      <item>
+        <p>The heading's <gui>+</gui> adds a channel. <gui>Edit graph</gui>, on a channel's page,
+        shows the graph editor:
+        nodes as boxes, click a box to select it and edit its parameters beside the canvas.</p>
+      </item>
+      <item>
+        <p>Inside the editor, <gui>add node</gui> is a menu button whose popover picks the op,
+        so the node arrives as the operation you asked for.</p>
+      </item>
+    </steps>
+  </section>
+
+  <section id="gestures">
+    <title>Graph gestures</title>
+    <p><gui>drag</gui> from an output port to an input port to wire them; drag a wired input
+    port off its connection to detach it; click a wire and press <key>Delete</key> to remove
+    it; drag a box to move it. <gui>Wheel</gui> zooms about the pointer. <gui>Drag the
+    background</gui> to pan. <key>f</key> fits all nodes into view;
+    <keyseq><key>Ctrl</key><key>0</key></keyseq> resets the view. <gui>tidy</gui>, the button
+    beside <gui>fit</gui> in the editor, lays the graph out in topological columns and frames
+    it. The orange dot marks the output node; click <gui>set as output</gui> to move it.</p>
+  </section>
+
+  <section id="knowing">
+    <title>Worth knowing</title>
+    <list>
+      <item><p>The graph is evaluated as an ordered list, so a node may only read ones
+      <em>above</em> it. A wire drawn right to left re-sorts the list silently so the graph
+      stays valid. A cycle is unrepresentable: the connection is refused rather than created,
+      and the line beneath the form says why — a loop, or a node asked to read itself.</p></item>
+      <item><p>A derived channel <em>is</em> a channel. It is listed with the signals, gets a badge once computed, can be
+      plotted, measured, exported, and used as a source for another math channel.</p></item>
+      <item><p>The math runs on the <em>stored</em> samples — decimated and averaged — so a
+      cutoff you type in Hz means the rate the filter will actually run at. Change the window
+      across a decimation boundary and the coefficients are rebuilt for the new rate.</p></item>
+      <item><p>A source may only name an <em>acquired</em> channel. The stream's timestamp
+      signal is not one: a graph sourced from it validates and then reads NaN for ever, so the
+      dropdown does not offer it.</p></item>
+      <item><p>The output defaults to the <em>last</em> node, and a node added to a linear
+      graph becomes the output. Choosing an earlier node explicitly is respected.</p></item>
+      <item><p>Every numeric field starts at its own identity value — gain 1, offset 0 — not
+      at the bottom of its range.</p></item>
+    </list>
+  </section>
+
+  <section id="why">
+    <title>Why an operation sometimes does nothing</title>
+    <p>A graph's <em>output</em> is the node whose value becomes the channel, and it is drawn
+    as the orange dot. A new graph is built source, then operation, and the last node added
+    becomes the output — but a graph whose output is left on the source is valid and simply
+    passes its input through, which is the usual reason a gain or a filter appears to have no
+    effect. <gui>Set as output</gui> moves the dot.</p>
+
+    <p><gui>Apply</gui> is insensitive while the graph is incomplete. A line beneath the form
+    says why: an input that is not connected, no output chosen, or a <em>channel</em> node
+    naming a signal the scope is not acquiring. Only the channels being acquired are offered,
+    because a source that is not acquired reads as no data for ever — and a graph that reads
+    NaN is harder to diagnose than one that would not save.</p>
+
+    <p>The filters are real filters. A math channel's samples are produced as the stream
+    arrives, once per stored slot, so a low pass carries the history a filter needs. A cutoff
+    typed in hertz is against the <em>stored</em> rate, which is the wire rate until a wide
+    window makes the buffer decimate — the status line's rate is that number, and the filters
+    are rebuilt whenever it changes.</p>
+
+    <figure>
+      <title>The math channel editor</title>
+      <desc>Nodes as boxes on a canvas, the orange dot marking the output, and the selected
+      node's parameters beside it.</desc>
+      <media type="image" mime="image/png" src="figures/math-editor.png" width="938" height="420">
+        <p>A sine source wired through a gain into a filter, with the output on the last
+        node.</p>
+      </media>
+    </figure>
+  </section>
+
+  <section id="example">
+    <title>Example</title>
+    <p><code>[sine] → [gain x2]</code> gives a channel reading <code>y=[-2, 2]</code>. A
+    100 Hz low pass on the same source passes 50 Hz at 0.97 and 2 kHz at 0.002; a 1 kHz band
+    pass with Q=2 passes 200 Hz at 0.05, 1 kHz at 0.95 and 4 kHz at 0.05. Each derived channel
+    must hold exactly as many samples as the shared clock has time slots.</p>
+  </section>
+
+</page>

help/C/org.udpscope.app/measurements.page

@@ -0,0 +1,159 @@
+<page xmlns="http://projectmallard.org/1.0/"
+      type="topic" style="task"
+      id="measurements">
+
+  <info>
+    <link type="guide" xref="index#analysis"/>
+    <link type="seealso" xref="cursors"/>
+    <desc>A measurement is a statistic of one signal over the window the pane is about — the
+    visible range, or the frozen frame while a view is pinned — with optional
+    on-plot marks and a per-measurement statistics line.</desc>
+    <credit type="author copyright">
+      <name>Martino Ferrari</name>
+    </credit>
+  </info>
+
+  <title>Measurements</title>
+
+  <p>A measurement is a statistic of one signal over the window the pane is about, recomputed as
+  that window moves. The pane lists them with their values; each can also draw its result on
+  the plot.</p>
+
+  <p>That window is the <em>visible range</em> — so on a live view the numbers follow what you
+  pan and zoom to. On a <em>still frame</em> — a held event, a paused stream, an opened file — it
+  is the frame's own extent instead, so panning or zooming inside it changes nothing: the data
+  being measured has not changed and you are only looking closer.</p>
+
+  <section id="reach">
+    <title>How to reach it</title>
+    <steps>
+      <item>
+        <p>Press <key>m</key>, or <gui>Edit</gui> beside <gui>Measurements</gui> in the dock. Either opens the
+        <gui>Measurements</gui> page over the plot; the dock itself shows each measurement's value,
+        and a click on one opens its dialog.</p>
+      </item>
+      <item>
+        <p>The page's <gui>+</gui> adds one; clicking a row opens the dialog where the signal,
+        the type, the threshold share or shares and the on-plot marks are set, with
+        <gui>Save</gui> and <gui>Delete</gui>.</p>
+      </item>
+    </steps>
+  </section>
+
+  <section id="knowing">
+    <title>Worth knowing</title>
+    <list>
+      <item><p>The types are average, top, bottom, min, max, peak to peak, amplitude, above,
+      below, between, pulse duration, period and frequency. <gui>top</gui> and <gui>bottom</gui> are the waveform's
+      <em>flat</em> high and low levels: the level the signal dwells at, taken from the densest
+      band of the window on each side of the split. A band-limited edge overshoots and rings —
+      a nominal 2 V square reaches about ±1.18 at its edges — and a ripple or an overshoot is
+      therefore <em>not</em> what these read. <gui>amplitude</gui> is the delta between those two
+      levels, and <gui>peak to peak</gui> is the swing between the extremes (so on a rippled
+      square <gui>amplitude</gui> reads 2 V where <gui>peak to peak</gui> reads 2.36 V).</p></item>
+      <item><p><gui>above</gui>, <gui>below</gui> and <gui>between</gui> are the opposite kind of
+      number: the plain <em>mean of the samples</em> above a share, below it, or between two
+      shares. That is a different question from <gui>top</gui>/<gui>bottom</gui> even about the
+      same split, and it is the older one — on a unit sine <gui>above 50%</gui> reads 0.64 V
+      (2/π, the mean of a half cycle) where <gui>top</gui> reads 0.96 V (near the peak, which is
+      where a sine dwells most), and on a band-limited square <gui>above 50%</gui> reads 0.99 V
+      where <gui>top</gui> reads the plateau, 1.00 V: the edge's ring is inside the first and not
+      inside the second. <gui>between</gui> takes <em>two</em> shares — <gui>from %</gui> and
+      <gui>to %</gui> — and reports the mean of the samples inside that band, which no single
+      split can answer; the order you type them in does not matter, since a band between 80 % and
+      20 % is the band between 20 % and 80 %.</p></item>
+      <item><p>A mean over a side carries whatever is on that side, so these three are the right
+      numbers when you want the <em>energy</em> or the <em>offset</em> of part of the waveform,
+      and the wrong ones when you want the level a plateau sits at. Like every other measurement,
+      one with nothing to measure reads <code>--</code> rather than a made-up number: a share at
+      100 % has no sample above it, and a band can hold none at all — on an ideal
+      (non-ringing) square every sample is exactly ±1, so a band between 50 % and 75 % is
+      empty.</p></item>
+      <item><p><gui>top</gui> and <gui>bottom</gui> also read <em>near the peak</em> on a
+      waveform that has no flat part, which is the honest reading rather than a failure: a unit
+      sine has no plateau, so the densest band is at its peak and these read about ±0.96 — not
+      the 0.64 a mean over each half would give, and not ±1 either. Only a level the signal
+      actually dwells at is a level.</p></item>
+      <item><p>The <em>split</em> says which side a level is read from, so any share between the
+      two levels reads the same number; it is not a boundary the value depends on. The one case
+      where it is read directly is a window the scope cannot summarize by level — a window
+      shorter than a level's own resolution, or one read through <gui>hf</gui> — where
+      <gui>top</gui>/<gui>bottom</gui> fall back to the mean of each side of the split and
+      <gui>amplitude</gui> to the window's peak to peak.</p></item>
+      <item><p>The on-plot marks come in two kinds and the mix is the reading: a <em>level</em>
+      mark is a ruler at a value, a <em>time</em> mark is a marker at a position. An average
+      draws one level mark; a max draws a level mark <em>and</em> a time mark at the first
+      sample that reached it; <gui>peak to peak</gui> draws a ruler at each extreme and
+      <gui>amplitude</gui> a ruler at each of its two flat levels — the pair is the span, so
+      the two rulers <em>are</em> the measurement.</p></item>
+      <item><p>Marks cannot be dragged. A measurement mark says what the measurement measured,
+      so it is created unselectable — as is the trigger marker.</p></item>
+      <item><p>A pass is throttled to a cadence rather than run every frame, so a ruler over a
+      live view is <em>stepped</em>. The number and the ruler come from the same pass, so they
+      always agree.</p></item>
+      <item><p>An invalid pass keeps its <em>level</em> marks and drops its <em>time</em>
+      marks. A level is a property of the signal and outlives the window; a position inside
+      the window does not. That is what stops the rulers blinking off at a mode change.</p></item>
+      <item><p>A crossing is counted with <em>hysteresis</em>, not on a bare level: the
+      thresholds are a tenth of the window's peak to peak either side of the share, and an
+      edge is counted only once the signal has passed the far one. Period, frequency and pulse
+      duration all depend on it. The mid level is exactly where a waveform moves fastest, so
+      any interferer faster than the fundamental recrosses a single level several times per
+      real crossing — a 5 Hz sine with a 500 Hz tone at a tenth of the amplitude reads 39 Hz
+      without the band and 5 Hz with it. The band holds to an interferer a third of the
+      waveform's own size.</p></item>
+      <item><p>The band is clamped to stay inside the data, which is what keeps a threshold set
+      near an extreme usable: a fixed band there would sit above every sample and the
+      measurement would read nothing. A share near an extreme still leaves the band little
+      room, so it rejects less — which is one reason period and frequency offer no share to
+      set.</p></item>
+      <item><p>A window with too few crossings reads <code>invalid</code> / <code>--</code>
+      rather than a plausible invented number. Frequency over a window holding one edge is the
+      usual case.</p></item>
+      <item><p><gui>frequency</gui> is reported in Hz and <gui>period</gui>/<gui>pulse
+      duration</gui> in seconds; every other type carries the channel's own unit. A value is
+      written with a <em>metric prefix</em> so its digits sit in <code>1..999</code> —
+      <code>636.62 mV</code>, not <code>0.64 V</code> — including when the stream declares no
+      unit at all, which is always the case for a math channel: there the prefix goes tight
+      against the number (<code>636.62m</code>), since two decimals of an unprefixed small
+      value is <code>0.00</code>.</p></item>
+      <item><p>Cost is bounded by reading the summary pyramid the producer already maintains,
+      not the raw window: a bucket's sum is a sum, so the mean, the extremes and a level's own
+      mean are exact. <gui>top</gui>, <gui>bottom</gui> and <gui>amplitude</gui> read the
+      <em>density</em> of the window out of that same summary — which is what tells a flat level
+      from a ripple — so those three cost a second read of the summary and never of a sample, and
+      <gui>between</gui>'s second share is one more level in the same summary walk rather than a
+      walk of its own.</p></item>
+      <item><p><gui>Statistics</gui> adds a second line to every measurement showing
+      <code>n</code>, the mean, the standard deviation and the range. Each observation is one
+      <em>recompute</em> of the pane, so <code>n</code> counts windows measured, not samples —
+      a mean frequency over many windows is what that claims to be. <gui>Reset</gui> clears
+      every accumulator and starts fresh. A change of display window, a CONFIG or a
+      measurement edit also resets; a pause, a resume, a zoom, a pan and the toggle itself do
+      not, so turning the line off to read the plot and back on again keeps the history. On a
+      still frame a pan or a zoom changes nothing for the history to record in the first place —
+      the values do not move there at all.</p></item>
+    </list>
+  </section>
+
+  <section id="example">
+    <title>Example</title>
+    <p>On a 1 Hz ±1 sine: <code>average=0</code>, <code>top=0.957988</code>,
+    <code>bottom=-0.957988</code> (the flat levels, near the peaks — a sine has no plateau),
+    <code>max=1</code>, <code>min=-1</code>,
+    <code>peak to peak=2</code>, <code>amplitude=1.915983</code>, <code>pulse duration=0.5 s</code>
+    (duty 0.5), <code>period=1 s</code>, <code>frequency=1 Hz</code>. On the same stream's
+    band-limited <code>square</code>, whose edges ring out to ±1.179: <code>top=0.999983</code>,
+    <code>bottom=-0.999983</code>, <code>amplitude=1.999966</code> against
+    <code>peak to peak=2.358701</code> — the levels are the plateau's and the extremes are the
+    edges'. Over a 2 M-sample window those passes read about 0.1% of the samples.</p>
+    <p>The mean-over-a-side types on the same two windows: on the sine
+    <code>above 50=0.636620</code>, <code>below 50=-0.636620</code> and
+    <code>between 50 75=0.255873</code>; on the rippled square <code>above 50=0.986496</code> and
+    <code>between 50 75=0.302744</code>, against <code>1.000000</code> for the same
+    <code>above 50</code> on an ideal (non-ringing) square. A <code>ramp</code>, whose density is
+    uniform, is the shape that names what a band mean <em>is</em>: <code>above 50=0.500000</code>
+    and <code>between 50 75=0.250000</code>, each band's own centre.</p>
+  </section>
+
+</page>

help/C/org.udpscope.app/navigate.page

@@ -0,0 +1,104 @@
+<page xmlns="http://projectmallard.org/1.0/"
+      type="topic" style="task"
+      id="navigate">
+
+  <info>
+    <link type="guide" xref="index#viewing"/>
+    <link type="seealso" xref="window"/>
+    <desc>Panning, zooming and fitting the plot with the mouse and the keyboard, and what a
+    pinned view refuses to do.</desc>
+    <credit type="author copyright">
+      <name>Martino Ferrari</name>
+    </credit>
+  </info>
+
+  <title>Navigating the plot</title>
+
+  <p>The plot pans and zooms with the mouse and with the keyboard. Every gesture acts on the
+  row the pointer is over, and because the rows share one time axis, an x change moves all of
+  them.</p>
+
+  <section id="reach">
+    <title>How to reach it</title>
+    <terms>
+      <item>
+        <title>Wheel</title>
+        <p><gui>Wheel</gui> zooms both axes · <gui>Shift</gui>+<gui>Wheel</gui> zooms x only ·
+        <gui>Ctrl</gui>+<gui>Wheel</gui> zooms y only.</p>
+      </item>
+      <item>
+        <title>Drag</title>
+        <p><gui>Drag</gui> pans · <gui>Shift</gui>+<gui>Drag</gui> is a box zoom on both axes ·
+        <gui>Ctrl</gui>+<gui>Drag</gui> on x only · <gui>Alt</gui>+<gui>Drag</gui> on values
+        only. The area being chosen is framed while you drag it, so you can see what the
+        release will apply.</p>
+      </item>
+      <item>
+        <title>Keyboard</title>
+        <p><key>+</key> and <key>-</key> zoom both axes; <key>Ctrl</key> with them restricts
+        to x, <key>Alt</key> to y. <gui>Arrow keys</gui> pan, <key>f</key> fits,
+        <key>Escape</key> cancels a gesture in progress.</p>
+      </item>
+    </terms>
+
+    <p>The full table is in the shortcut overview (<keyseq><key>Ctrl</key><key>/</key></keyseq>).</p>
+  </section>
+
+  <section id="knowing">
+    <title>Worth knowing</title>
+    <list>
+      <item><p>The keyboard zoom's modifiers are <em>not</em> the wheel's, and that is
+      deliberate: on common layouts <key>+</key> <em>is</em> <keyseq><key>Shift</key><key>=</key></keyseq>,
+      so a bare zoom-in already arrives with Shift set and Shift could not mean anything.
+      Ctrl/Alt mirror the box-zoom drags instead.</p></item>
+      <item><p>A <em>pinned</em> view is navigable within its own data but cannot leave it.
+      While an event is held, a capture is filling, or the view is paused, a zoom <em>in</em>
+      works normally — "not outside the event" is not "not readable" — but a pan or a zoom out
+      is clamped to the data.</p></item>
+      <item><p>Nothing you do on the plot changes the <em>time window</em> — only the header
+      control does. A zoom or a pan moves the view inside the window; <key>f</key> (and
+      <gui>Fit X axis</gui>) is the <em>undo</em> of a zoom, so a 2 s window zoomed into reads
+      2 s again. The window is more than the axis: it is also the trigger's event span and how
+      the samples are stored, so a wheel notch that redefined it would re-plan the buffer and
+      drop your history.</p></item>
+      <item><p>The axis does not scroll — the <em>data</em> does. A live axis is a fixed
+      <code>[-window .. 0]</code> with the newest sample at 0, so the labels stand still and
+      the trace rolls under them. The cursors stand still with the labels (they are positions
+      on screen, so a cursor you placed stays where you put it, over newer data each frame),
+      while a measurement's marks travel with the sample they measured and leave the view when
+      it does.</p></item>
+      <item><p>A live view is clamped to the window you asked for, not to what the ring
+      happens to hold. That is why a buffer that has only just started filling leaves its
+      left-hand side empty instead of squeezing the window down to the first few
+      samples.</p></item>
+      <item><p>Zooming hard into a held capture is exact. The renderer finds the visible
+      samples by binary search over the real timestamps, never over a nominal sample grid, so
+      a capture whose clock wandered does not drift away from its axis as you zoom.</p></item>
+      <item><p>A trace holding far more samples than the plot has pixels is drawn <em>one
+      pixel column at a time</em>: each column is a single vertical line from the lowest to
+      the highest value that falls in it. Drawn as a polyline instead, such a window puts
+      three or four near-vertical lines in every column at slightly different sub-pixel
+      positions, and how they overlap beats against the pixel grid — which reads as bands of
+      light and dark that <em>crawl</em> as you pan. One line per column removes the beat, and
+      it is also much faster: a 1 MS/s view costs a couple of thousand line segments a frame
+      instead of a couple of hundred thousand.</p></item>
+      <item><p>Those columns are <em>graded by brightness</em>, the way a digital-phosphor
+      scope reads: bright where the signal spent its time, faint where it only passed through.
+      A column's highest and lowest value are the same whether the samples in it are spread
+      evenly or piled at its two ends, so the grading is what tells the two apart — the flat
+      parts of a square wave come out solid and the edges between them faint. It is read from
+      a finer division of each column rather than from the line that is drawn, and it costs
+      about a millisecond a frame.</p></item>
+    </list>
+  </section>
+
+  <section id="example">
+    <title>Example</title>
+    <p>Pause a live view, then press <keyseq><key>Ctrl</key><key>+</key></keyseq>: x narrows
+    and y does not move. Press <keyseq><key>Alt</key><key>+</key></keyseq>: y narrows and x
+    does not. Eight doublings into a held 2 s capture, the trace still reaches both margins —
+    the zoom probe reports <code>gap_px</code> and <code>end_px</code> within a pixel or two
+    at every step.</p>
+  </section>
+
+</page>

help/C/org.udpscope.app/overview.page

@@ -0,0 +1,227 @@
+<page xmlns="http://projectmallard.org/1.0/"
+      type="topic" style="task"
+      id="overview">
+
+  <info>
+    <link type="guide" xref="index#main"/>
+    <desc>What udpscope plots, the parts of the window, and one pass through the
+    application from connecting to saving.</desc>
+    <credit type="author copyright">
+      <name>Martino Ferrari</name>
+    </credit>
+  </info>
+
+  <title>Overview</title>
+
+  <section id="what">
+    <title>What udpscope is</title>
+    <p>udpscope plots a live UDPStreamer source. One window holds up to eight rows of plots,
+    each with up to four traces, and every row shares one time axis, so the whole figure
+    scrolls together. Acquisition runs on its own thread and writes a ring buffer sized from
+    <cmd>--buffer-samples</cmd>; the drawing thread reads whatever that ring holds when a frame
+    starts, which is why a trace never makes the window stutter.</p>
+
+    <p>The stream is the clock. Every interval you read on screen is measured between
+    timestamps the source sent, never your machine's, so a stalled source freezes the view
+    instead of scrolling it — and a source whose clock steps still gets the window you asked
+    for.</p>
+
+    <p>The time axis is <em>relative to now</em>. While streaming it is a fixed
+    <code>[-window .. 0]</code> with the newest sample at 0, so x reads as an age:
+    <code>-1.5s</code> is a sample a second and a half old. In trigger mode 0 is the event's
+    edge instead, and a paused view keeps the ages it was frozen with. The source's own clock
+    is still there when you need it — an export writes it as a second column.</p>
+
+    <figure>
+      <title>The udpscope window</title>
+      <desc>The header bar above the plots, the badge bar and the status bar under them, and
+      the dock on the right.</desc>
+      <media type="image" mime="image/png" src="figures/main-window.png" width="1280" height="800">
+        <p>One figure of three rows with three signals plotted, a badge for each in the badge
+        bar, the dock with its readouts and its events block, and the status bar reading
+        <gui>live</gui>.</p>
+      </media>
+    </figure>
+  </section>
+
+  <section id="reach">
+    <title>How to reach it</title>
+    <p>Start the app with a source
+    (<cmd>udpscope --server 127.0.0.1 --port 8000</cmd>), or start it with no
+    <cmd>--server</cmd> and pick one from the chooser, which lists the sessions you have
+    opened before. A unicast source serves one client at a time: if a second viewer connects,
+    they take turns and the status bar says so. To watch one source from several instances,
+    use <cmd>--multicast</cmd> with the group and <cmd>--interface</cmd> with the local
+    address.</p>
+
+    <p>The signals arrive <em>disabled</em>. Nothing is acquired until you turn one on in the
+    signal list, and enabling is what starts acquisition — so a freshly opened scope with an
+    empty badge bar is working correctly, not failing to connect. For the same reason a start
+    that has enabled nothing prints no <code>buffer allocated:</code> line on stderr.</p>
+
+    <note style="warning">
+      <p>Over SSH with X11 forwarding the window may never appear, and the cure is
+      <cmd>udpscope --renderer cairo</cmd>. Two symptoms tell the two halves apart: a
+      <code>vkCreateSwapchainKHR() ... VK_ERROR_INITIALIZATION_FAILED</code> warning is
+      GTK's default Vulkan renderer failing to make a swapchain and is what the option's
+      <code>GSK_RENDERER=cairo</code> answers; a window whose allocation stays zero
+      (<code>window_button_w=0</code>) means the plot's GL area has no context either, and
+      that is what its <code>LIBGL_ALWAYS_SOFTWARE=1</code> answers. Both variables are
+      exported before GTK initialises, because they are read when the renderer and the GL
+      context are created. <cmd>--renderer gl</cmd> is faster when indirect GL works.</p>
+    </note>
+
+    <note style="tip">
+      <p>See <link xref="source">Choosing a source</link> for the chooser and the multicast
+      options in full.</p>
+    </note>
+  </section>
+
+  <section id="window">
+    <title>The window</title>
+    <terms>
+      <item>
+        <title>The header bar</title>
+        <p>Left to right: the time window (<gui>2 s</gui>), the trigger and the pause; then, on
+        the right, the cursors switch, the dock switch and the menu, which holds
+        <gui>Fit to data</gui>, the <gui>Layout editor</gui>, <gui>Export visible range</gui>,
+        <gui>Configurations</gui>, <gui>Help</gui>, <gui>Preferences</gui> and
+        <gui>About</gui>. The trigger button turns trigger mode on and off; the trigger's
+        settings are in the panel its badge opens.</p>
+      </item>
+      <item>
+        <title>The plot</title>
+        <p>Up to eight rows, each with its own y axis and up to four traces, all on one shared
+        time axis. Right-click a row for its own menu (fit, add a signal, remove a trace).</p>
+      </item>
+      <item>
+        <title>The badge bar</title>
+        <p>The strip under the plot. On the left, one badge for each signal you have switched
+        on, then a <gui>+</gui>; past six signals they fold into a single <gui>N signals</gui>
+        badge. On the right, <gui>Trigger</gui>, which names the trigger's state, and <gui>Source</gui>, which is there only when the
+        source has controls of its own. A badge opens its page in the panel described next;
+        a signal's badge is also what you drag onto a row.</p>
+      </item>
+      <item>
+        <title>The side panel over the plot</title>
+        <p>One panel, 360 px wide, slides over the plot's right edge and shows one page at a
+        time: the trigger, a signal's colour, calibration and rows, the list of signals to
+        add, the cursors, the measurements, the events, or a source's own controls. It closes
+        with a second click on the badge that opened it, with <key>Esc</key>, with
+        <gui>Close</gui>, or with a click on the plot, and it never resizes the plot.</p>
+      </item>
+      <item>
+        <title>The dock</title>
+        <p>The column on the right, which the dock button in the header bar (<key>s</key>)
+        shows and hides. Its <gui>Readouts</gui> are a read-only copy of the cursors and of
+        every measurement; <gui>Edit</gui> beside each heading opens that instrument's full
+        page. Under them, <gui>Events</gui> lists the captured events, newest first; a click
+        replays one and <gui>Manage</gui> opens the full list. While the dock is hidden, or the window is narrow and the
+        dock slides over the plot, the readouts show in a strip under the plot instead, as long as the cursors are on or there is a measurement.</p>
+      </item>
+      <item>
+        <title>The status bar</title>
+        <p>The last line, under the badge bar — the state word, the stored sample rate and
+        the window, and the ⓘ beside it for packets, gaps and the buffer's own figures. The
+        second screenshot below is what a capture looks like: the trigger marker at the edge
+        and the axis pinned to the event.</p>
+      </item>
+    </terms>
+
+    <figure>
+      <title>A held capture</title>
+      <desc>The trigger has latched, the state reads <gui>event held</gui>, and the axis is
+      pinned to the event rather than to the live edge.</desc>
+      <media type="image" mime="image/png" src="figures/trigger-capture.png" width="1280" height="800">
+        <p>The trigger marker sits at x = 0 and the pre-trigger share of the window is drawn
+        to its left.</p>
+      </media>
+    </figure>
+  </section>
+
+  <section id="first">
+    <title>The first five minutes</title>
+    <steps>
+      <item>
+        <p><em>Connect.</em> With no <cmd>--server</cmd>, pick a stored session or type a host
+        and port.</p>
+      </item>
+      <item>
+        <p><em>Enable a signal</em> in the <gui>Signals</gui> page (the <gui>+</gui> badge, or <key>g</key>). The plot stays empty for the first
+        fraction of a second while the first window fills — the buffer holds only what has
+        arrived.</p>
+      </item>
+      <item>
+        <p><em>Drag its badge onto a row.</em> Drop a second signal on another row, or the same
+        signal again for a second view of it. The colour is per signal, so it is the same one
+        wherever it appears.</p>
+      </item>
+      <item>
+        <p><em>Set the window</em> with the control in the header bar: type a number, pick a
+        unit, or step a decade. The trigger's event window is a share of this span, so a
+        window change moves it.</p>
+      </item>
+      <item>
+        <p><em>Pause</em> (<key>space</key>) to look at a still picture; the producer keeps
+        filling the buffer behind it, and resuming shows what arrived meanwhile rather than a
+        hole.</p>
+      </item>
+      <item>
+        <p><em>Arm the trigger</em> (<key>a</key>) and wait for a latch: the view freezes on
+        one event, and you can zoom in on it. Disarming mid-capture keeps what the capture
+        got.</p>
+      </item>
+      <item>
+        <p><em>Measure it</em> — press <key>m</key>, or <gui>Edit</gui> beside
+        <gui>Measurements</gui> in the dock. A measurement is a statistic of the visible
+        window, its value is shown in the dock, and <gui>show on plot</gui> marks it as a
+        ruler or a pair of markers.</p>
+      </item>
+      <item>
+        <p><em>Save the data</em> with <gui>Export visible range</gui>, which writes the
+        plotted signals over the window at the stored rate to <file>.npy</file>,
+        <file>.csv</file> or <file>.mf3</file> (MDF 3.30).</p>
+      </item>
+    </steps>
+  </section>
+
+  <section id="knowing">
+    <title>Worth knowing</title>
+    <list>
+      <item><p>A signal nobody enables costs nothing — no buffer, no socket work, no
+      measurements.</p></item>
+      <item><p>The window remembers itself. Rows, traces, the time window, calibration, which
+      signals were enabled, the math channels with their graphs, and the measurements are
+      written per host and port, and reloaded the next time you open that source.</p></item>
+      <item><p>A very wide window on a fast stream is drawn from averaged groups of samples,
+      so the rate in the status bar falls: that is the anti-alias filter, not a fault —
+      striding would fold a fast signal back as a slow one, which looks entirely plausible on
+      screen.</p></item>
+      <item><p>Every instrument the app computed — the trigger marker, the measurement marks
+      — is locked to the pointer's reach. The cursors are yours to drag; those are not.</p></item>
+    </list>
+  </section>
+
+  <section id="installing">
+    <title>Installing this manual</title>
+    <p>The manual is a help set the desktop viewer reads off disk, so <key>F1</key> opens it only
+    once a copy sits where <cmd>help:</cmd> resolves. Either of two targets installs it on its own,
+    without building the application, and each prints where it wrote. Prefer the system-wide one:
+    it is the copy every viewer can read, and the reason is worth knowing before you pick the
+    other:</p>
+    <list>
+      <item><p>For a system-wide or packaged install:
+      <cmd>cmake --build build --target install-help</cmd> writes it under the configured
+      <cmd>CMAKE_INSTALL_PREFIX</cmd>, so point that at <file>/usr</file>
+      (<cmd>cmake -DCMAKE_INSTALL_PREFIX=/usr ..</cmd>) and wrap the target in
+      <cmd>sudo</cmd>. A viewer reads its figures as separate files, and its sandbox exposes the
+      system help directories, so this copy always shows them.</p></item>
+      <item><p>For your own account, needing no root:
+      <cmd>cmake --build build --target install-help-user</cmd> writes it under
+      <file>$XDG_DATA_HOME</file> (default <file>~/.local/share</file>). Be aware that the same
+      sandbox does <em>not</em> expose the user's data directory: those pages open, but a viewer
+      such as Yelp shows them without their figures.</p></item>
+    </list>
+  </section>
+
+</page>

help/C/org.udpscope.app/pause.page

@@ -0,0 +1,63 @@
+<page xmlns="http://projectmallard.org/1.0/"
+      type="topic" style="task"
+      id="pause">
+
+  <info>
+    <link type="guide" xref="index#viewing"/>
+    <link type="seealso" xref="trigger"/>
+    <desc>Pausing freezes the display without stopping the stream, and the status bar says how
+    long you have been paused.</desc>
+    <credit type="author copyright">
+      <name>Martino Ferrari</name>
+    </credit>
+  </info>
+
+  <title>Pause and play</title>
+
+  <p>Pause freezes the <em>display</em>, not the acquisition. The producer keeps filling the
+  ring at full rate; the view binds an immutable snapshot of the window that was on screen,
+  and the axis is pinned to it.</p>
+
+  <section id="reach">
+    <title>How to reach it</title>
+    <steps>
+      <item>
+        <p>Press the pause button in the header bar, or <key>Space</key>.</p>
+      </item>
+      <item>
+        <p>Press it again to resume, which rebinds the live ring and puts the window back on
+        the newest data.</p>
+      </item>
+    </steps>
+  </section>
+
+  <section id="knowing">
+    <title>Worth knowing</title>
+    <list>
+      <item><p>Nothing is lost while paused. Because the producer never stops, resuming shows
+      current data with no hole in the history behind it.</p></item>
+      <item><p>The axis is pinned to the <em>snapshot's own stamps</em>, not to the window that
+      was requested. A window reaching back past the oldest retained sample yields a shorter
+      snapshot, and the pinned axis is that shorter span — so you see a narrower view rather
+      than an empty margin.</p></item>
+      <item><p>A paused view is pinned exactly as a held trigger event is: zoom in freely, but
+      a pan or a zoom out is clamped to the snapshot's data. A measurement goes on describing
+      that frozen frame rather than the part of it you are looking at, so a zoom on a pause
+      changes no reading — see <link xref="measurements"/>.</p></item>
+      <item><p>Pausing is the easiest way to measure a layout or read a cursor precisely,
+      because nothing under the pointer moves between frames.</p></item>
+      <item><p>The status bar says how long you have been paused — wall time, since the stream
+      itself never stopped. It is there so a frozen picture cannot be mistaken for a live one
+      that went quiet.</p></item>
+    </list>
+  </section>
+
+  <section id="example">
+    <title>Example</title>
+    <p>Pause with a 2 s window over a ring holding 1.4 s: the frozen axis reads
+    <code>[-1.40 .. 0.00]</code> rather than <code>[-2.00 .. 0.00]</code> with 0.6 s of blank.
+    The pause probe reports <code>ring_produced</code> still growing across the pause and
+    <code>event_size</code> non-zero exactly while paused.</p>
+  </section>
+
+</page>

help/C/org.udpscope.app/sessions.page

@@ -0,0 +1,93 @@
+<page xmlns="http://projectmallard.org/1.0/"
+      type="topic" style="task"
+      id="sessions">
+
+  <info>
+    <link type="guide" xref="index#output"/>
+    <link type="seealso" xref="source"/>
+    <desc>Per-source configuration files: where they live, what they persist, and how the
+    chooser and the Configurations dialog use them.</desc>
+    <credit type="author copyright">
+      <name>Martino Ferrari</name>
+    </credit>
+  </info>
+
+  <title>Sessions and settings</title>
+
+  <p>udpscope stores named sessions — <em>configurations</em> — per source, so reopening a
+  source gives you the scope you closed, and one source can hold several arrangements for
+  different experiments. There is no global preferences file: the session <em>is</em> the
+  settings.</p>
+
+  <section id="reach">
+    <title>How to reach it</title>
+    <p>Nothing to open — the file is written as you work. Its path is in the About dialog, and
+    the directory is <file>$XDG_CONFIG_HOME/udpscope</file>, or <file>~/.config/udpscope</file>
+    when that is unset. Each source has a directory <file>&lt;host&gt;_&lt;port&gt;/</file>
+    holding one <file>&lt;name&gt;.toml</file> per configuration and an <file>active</file>
+    file naming the one it is on.</p>
+  </section>
+
+  <section id="configs">
+    <title>Configurations</title>
+    <p><gui>Configurations…</gui> in the menu lists the running source's configurations: click
+    a row to open it, <gui>×</gui> to delete it, or type a name and a note and press
+    <gui>Save this session</gui> to keep the current arrangement under a new one. Opening a
+    configuration saves the current session first, so switching never loses what it switches
+    from.</p>
+
+    <p>The startup chooser (start with no <cmd>--server</cmd>) lists one row per configuration,
+    with its note and its settings, so two arrangements of one source are told apart before
+    they open.</p>
+
+    <p>A configuration also carries the settings that can only be decided when the buffers are
+    allocated: the <gui>samples per signal</gui> (<cmd>--buffer-samples</cmd>), relative time, and the
+    packet capture's ring size. Opening a configuration from the chooser applies all three;
+    switching inside a running app applies the rest and says in the status line that these take
+    effect on the next start.</p>
+
+    <p>The chooser's form sets the first two for a new host, and its pencil button edits them
+    on an existing configuration — along with the name and the note. Renaming a configuration,
+    or editing the address it points at, moves it: the old file is removed rather than left
+    behind.</p>
+  </section>
+
+  <section id="knowing">
+    <title>Worth knowing</title>
+    <list>
+      <item><p>What a configuration persists: the time window, the rows and each row's slot
+      signals, the calibration, the trace colours, which signals were enabled, the math
+      channels with their graphs, the measurements — and the startup settings: samples
+      per signal, relative time and the packet capture's ring size.</p></item>
+      <item><p>Signal identity is the <em>name</em> throughout, because a new CONFIG renumbers
+      the channels.</p></item>
+      <item><p>A file written by a run against a source whose streamer was down would name no
+      signals at all, so such a run does <em>not</em> write: a configured session is never
+      overwritten by a run that configured nothing. (The chooser hides such a file for the same
+      reason.)</p></item>
+      <item><p>The multicast group and the interface live <em>inside</em> the file, because its
+      name cannot carry them. A file from an older build has neither key and loads as unicast
+      on the default route.</p></item>
+      <item><p>The chooser lists only configurations that name at least one signal, which is
+      what keeps it the sessions you configured rather than every port you have ever tested
+      against.</p></item>
+      <item><p>Deleting a configuration is a supported way to start over; the chooser's
+      <gui>×</gui> and the dialog's do exactly that.</p></item>
+      <item><p>A session from before configurations existed is imported once as the
+      configuration <code>default</code>, and the old file is kept beside the directory as
+      <file>&lt;host&gt;_&lt;port&gt;.toml.imported</file>.</p></item>
+    </list>
+  </section>
+
+  <section id="example">
+    <title>Example</title>
+    <p>Connect to <code>127.0.0.1:8000</code>, drop three signals on row 1, set a 2 s window,
+    and save the session as <code>bench</code> with a note.
+    <file>~/.config/udpscope/127.0.0.1_8000/bench.toml</file> now holds
+    <code>window_s=2 comment="…"</code> with
+    <code>signals = ["sine", "ramp", "noise", ""]</code>, and the next run reports
+    <code>layout loaded from …/127.0.0.1_8000/bench.toml</code> with those signals already
+    acquired.</p>
+  </section>
+
+</page>

help/C/org.udpscope.app/signals.page

@@ -0,0 +1,79 @@
+<page xmlns="http://projectmallard.org/1.0/"
+      type="topic" style="task"
+      id="signals">
+
+  <info>
+    <link type="guide" xref="index#main"/>
+    <link type="seealso" xref="layout"/>
+    <desc>How the source's CONFIG becomes channels, what enabling a signal starts, and how a
+    signal's scale and offset are calibrated.</desc>
+    <credit type="author copyright">
+      <name>Martino Ferrari</name>
+    </credit>
+  </info>
+
+  <title>Signals and calibration</title>
+
+  <p>The source's CONFIG message describes its signals: a name, a unit and a type. udpscope
+  turns each enabled signal into a <em>channel</em> — a ring of values beside the shared time
+  ring — and a channel is what a trace plots. Calibration is a scale and an offset applied at
+  ingest.</p>
+
+  <section id="reach">
+    <title>How to reach it</title>
+    <steps>
+      <item>
+        <p>Click the <gui>+</gui> badge in the badge bar, or press <key>g</key>. The
+        <gui>Signals</gui> page lists what can be added — the signals the source declares that
+        are not acquired yet, each with a tick that acquires it. Past six acquired signals the
+        badges fold into one <gui>N signals</gui> badge, and the page then lists every signal.</p>
+      </item>
+      <item>
+        <p>Once a signal is acquired its badge appears. Click it to open that signal's page: its
+        details directly under its name — <gui>Unit</gui>, <gui>Gain</gui> and <gui>Offset</gui>,
+        each with a pencil button that edits that one value, then the type, size, range, sample
+        rate and timing the stream declared — its colour and <gui>Plot on</gui> buttons for the
+        rows.</p>
+      </item>
+    </steps>
+  </section>
+
+  <section id="knowing">
+    <title>Worth knowing</title>
+    <list>
+      <item><p>Signals start disabled, and enabling one is what starts acquiring it. A trigger
+      on a signal nobody acquires can never fire, so arming a trigger enables its signal for
+      you.</p></item>
+      <item><p>A signal's page shows the gain and offset it is <em>currently</em> drawn
+      through, so a trace already scaled by a gain of 2 reads 2. The pencil beside a number opens
+      an editor for that number only, at its current value —
+      pressing <gui>Apply</gui> confirms it rather than resetting it. A signal nobody
+      calibrated shows the identity, 1 and 0. The unit can be renamed the same way (an empty
+      entry restores the one the stream declares); the new name is used in the readouts, the
+      measurements and the export, and is remembered with the session.</p></item>
+      <item><p>Calibration is applied <em>at ingest</em>, so changing it re-plans the buffer
+      and drops the history. So does enabling or disabling a signal, and so does a new
+      CONFIG. An empty plot for a second after one of those is the ring refilling, not a
+      fault.</p></item>
+      <item><p>The stream's first signal is usually its <em>timestamp</em>, and that one is
+      never acquired. It cannot be plotted, measured or used as a math source, and udpscope
+      refuses to put it in a row rather than binding a trace that would read nothing for
+      ever.</p></item>
+      <item><p>A signal's colour follows the <em>signal</em>, not the slot, so the same signal
+      on two rows is one colour, and the dot on its badge shows it. A signal on no row gets a
+      grey dot rather than none.</p></item>
+      <item><p><em>Change a signal's colour</em> with <gui>Change colour</gui> on its page; a
+      signal on no row has no trace to colour, so the button is dimmed. The colour is saved
+      with the session; <gui>Default colour</gui> on the same page gives the palette entry
+      back.</p></item>
+    </list>
+  </section>
+
+  <section id="example">
+    <title>Example</title>
+    <p>A source declaring <code>time</code>, <code>sine</code>, <code>ramp</code> and
+    <code>noise</code> yields three plottable signals. Enable all three and the exit dump
+    reads <code>3 signals, 3 channels</code>; <code>time</code> is not among them.</p>
+  </section>
+
+</page>

help/C/org.udpscope.app/source.page

@@ -0,0 +1,75 @@
+<page xmlns="http://projectmallard.org/1.0/"
+      type="topic" style="task"
+      id="source">
+
+  <info>
+    <link type="guide" xref="index#main"/>
+    <link type="seealso" xref="sessions"/>
+    <desc>How udpscope is pointed at a source: the command line, the startup chooser, and
+    opening an exported waveform instead of a live stream.</desc>
+    <credit type="author copyright">
+      <name>Martino Ferrari</name>
+    </credit>
+  </info>
+
+  <title>Choosing a source</title>
+
+  <p>A source is a host and a port, optionally reached through a multicast group on a named
+  interface. Pass it on the command line, or let udpscope ask.</p>
+
+  <section id="reach">
+    <title>How to reach it</title>
+    <steps>
+      <item>
+        <p>Run with <cmd>--server</cmd> and the app connects straight away.</p>
+      </item>
+      <item>
+        <p>Run <em>without</em> <cmd>--server</cmd> and a chooser appears first: one row per
+        stored <em>configuration</em> (<code>host:port · name</code>, its note, and the
+        settings it carries), newest first, plus a <gui>New host…</gui> form that takes the
+        address <em>and</em> the configuration it belongs to — its name and note, the
+        <gui>samples per signal</gui>, and whether time is relative or absolute. A row's pencil
+        button opens the same form on that configuration, pre-filled, and changes to its name
+        or address move it (the old file is deleted).</p>
+      </item>
+      <item>
+        <p>The second page, <gui>Waveforms</gui>, opens an <em>exported</em> run instead of a
+        live source: the files opened before (newest first; one that has since been deleted is
+        marked <em>missing</em>) and an <gui>Open…</gui> button for a new one. The same file
+        can be opened straight from the command line with <cmd>--open FILE</cmd>. A waveform
+        is a source that never arrives — no socket, no acquisition, no starvation notice — and
+        every instrument works on it: cursors, measurements, math channels and another export.
+        Only <file>.npy</file> files are read.</p>
+      </item>
+    </steps>
+
+    <p>The chooser runs before any buffer is allocated and before any socket is opened, so
+    declining it costs nothing.</p>
+  </section>
+
+  <section id="knowing">
+    <title>Worth knowing</title>
+    <list>
+      <item><p>The list is the sessions that <em>named a signal</em>. A session whose streamer
+      was down stores empty slot names and is filtered out, which is what keeps the list the
+      sources you actually configured rather than every port you have ever typed.</p></item>
+      <item><p>A stored row reconnects the way it was reached. The multicast group and the
+      interface are written inside the session file, because the file's name
+      (<file>host_port.toml</file>) cannot carry them.</p></item>
+      <item><p><cmd>--multicast</cmd> still needs <cmd>--server</cmd>: the CONFIG message is
+      fetched from the server, not from the group.</p></item>
+      <item><p>The <gui>×</gui> beside a row deletes that session file. Nothing else is
+      removed.</p></item>
+    </list>
+  </section>
+
+  <section id="example">
+    <title>Example</title>
+    <p><cmd>udpscope</cmd> with two stored sessions lists
+    <code>127.0.0.1:8000  plots=1 signals=3</code> and
+    <code>10.0.0.5:8001  plots=2 signals=4 multicast=239.1.2.3 interface=10.0.0.9</code>.
+    Activating the first reports <code>[sources] picked 127.0.0.1:8000</code> and continues
+    into the scope with that session's layout already loaded.</p>
+  </section>
+
+</page>

help/C/org.udpscope.app/status.page

@@ -0,0 +1,72 @@
+<page xmlns="http://projectmallard.org/1.0/"
+      type="topic" style="task"
+      id="status">
+
+  <info>
+    <link type="guide" xref="index#output"/>
+    <desc>The status bar's two tiers, the activity badge, the fixed state words, and the ⓘ
+    detail popover.</desc>
+    <credit type="author copyright">
+      <name>Martino Ferrari</name>
+    </credit>
+  </info>
+
+  <title>Status bar and diagnostics</title>
+
+  <p>The status bar is two tiers. The bar itself is one glance line — the state, the rate and
+  the window — and everything else is behind the ⓘ button at its right-hand end.</p>
+
+  <section id="reach">
+    <title>How to reach it</title>
+    <p>The bar is always visible at the foot of the window, under the badge bar. Click <gui>ⓘ</gui> for the detail popover.</p>
+  </section>
+
+  <section id="knowing">
+    <title>Worth knowing</title>
+    <list>
+      <item><p>The badge is one glyph in four colours: green <em>alternating</em> lit and dim
+      means data is arriving, and a steady colour means it is not. A badge that never blinks is
+      not a working badge. Of the two steady colours, <em>grey</em> is no stream at all or a
+      pipeline you stopped (the tooltip says which), and <em>yellow</em> is a source that
+      answered but has sent no configuration.</p></item>
+      <item><p>The state field is one word from a fixed set: <code>connecting</code>,
+      <code>live</code>, <code>paused</code>, <code>armed</code>, <code>capturing</code>,
+      <code>event held</code>, <code>disarmed</code>. Two states add one field each: in trigger
+      mode, how long ago the last event was; while paused, how long you have been paused.</p></item>
+      <item><p><code>connecting</code> means there is no <em>signal list</em> yet — either no
+      session or a session with no configuration behind it. Every other word claims a signal
+      list, so until one arrives there is nothing for them to describe: nothing can be enabled
+      and no data is owed.</p></item>
+      <item><p>The paused figure is <em>wall</em> time, not stream time — the producer never
+      stops while paused, so it answers "how long have I been looking at this picture".</p></item>
+      <item><p>Nothing on the bar may change width with the stream, because the bar sits
+      directly above the plot and a wider label would relayout it. That is why the rate
+      collapses to one figure or a range rather than listing per channel, and why an elapsed
+      time steps to a coarser unit instead of growing digits.</p></item>
+      <item><p><code>gaps</code> counts packets the receiver knows it missed. It is the number
+      that matters: a non-zero count means samples are absent from the buffer, not merely
+      late.</p></item>
+      <item><p><code>reconnects</code> counts sessions re-established with the source. Over
+      unicast a climbing count usually means a second client is taking the source's single
+      session.</p></item>
+      <item><p>The starvation notice — <em>connected, but no data is arriving</em> — is that
+      same situation seen from the other side: the signal list is here, so something took the
+      stream away. A source that has sent <em>no</em> configuration gets a different notice,
+      <em>trying to connect</em>, because nothing was taken away — pointing the app at a port
+      where nothing answers is that case, and the usual cause is a streamer that is not running
+      or is serving another port.</p></item>
+      <item><p><code>stored</code> versus <code>wire</code> in the popover is the decimation.
+      They differ exactly when the window is too long to store at full rate.</p></item>
+    </list>
+  </section>
+
+  <section id="example">
+    <title>Example</title>
+    <p>The bar reads <code>● live · 10 kS/s · 2 s window</code>. Behind ⓘ:
+    <code>Stream  connected, configured / packets 717 · frames 716 · gaps 0 / 3 signals · 3
+    channels</code>, <code>Buffer  200.0 MB · 1677 s span · time x1 / stored 10 kS/s (wire
+    10 kS/s)</code>, <code>Plot 1  3 traces · 195000 samples</code>,
+    <code>Reconnects  0</code>.</p>
+  </section>
+
+</page>

help/C/org.udpscope.app/trigger.page

@@ -0,0 +1,288 @@
+<page xmlns="http://projectmallard.org/1.0/"
+      type="topic" style="task"
+      id="trigger">
+
+  <info>
+    <link type="guide" xref="index#viewing"/>
+    <link type="seealso" xref="pause"/>
+    <desc>The trigger's four shapes, arming, forcing an acquisition and hold-off, the event cache with its replay,
+    compare and accumulate, and searching the buffer for a condition.</desc>
+    <credit type="author copyright">
+      <name>Martino Ferrari</name>
+    </credit>
+  </info>
+
+  <title>Trigger</title>
+
+  <p>The trigger watches one signal for a condition and captures a window around it. The
+  <gui>Shape</gui> dropdown chooses what counts as an event; the arming, hold-off, pre/post
+  window and Normal/Single mode are the same for all four shapes. The captured window is
+  frozen on screen until you re-arm.</p>
+
+  <section id="reach">
+    <title>How to reach it</title>
+    <steps>
+      <item>
+        <p>Click the <gui>Trigger</gui> badge at the right of the badge bar to open the
+        trigger page: the signal, the level, the shape, the edge (rising, falling, either), the
+        mode (Normal or Single) and the pre-trigger share. The trigger button in the header bar
+        (<key>t</key>) turns trigger mode on and off; it does not open the page.</p>
+      </item>
+      <item>
+        <p><gui>Arm</gui> starts watching; <key>a</key> arms and disarms from the keyboard.
+        When the page is locked with its edit button — so that it states what the
+        trigger is set to instead of showing the controls — <gui>Arm/Disarm</gui> is in its
+        heading, and the trigger can be armed or disarmed without unfolding the page. It is
+        offered only while trigger mode is on, because a trigger that is off has no engine to
+        arm.</p>
+      </item>
+      <item>
+        <p><gui>Force</gui> takes one acquisition <em>now</em>, with the event window above,
+        without waiting for the condition to hold — for when the event you are waiting for is not
+        coming and you want to see what the signal is doing this instant. The capture runs out its
+        post-trigger share and then freezes, exactly like a latch: the marker sits at the instant
+        you pressed. In <gui>Normal</gui> mode the trigger goes back to waiting afterwards; in
+        <gui>Single</gui> mode it disarms, because one acquisition is the whole of what that mode
+        means either way. It needs a signal to be acquired — the trigger cannot watch one that is
+        switched off — and pressing it while a capture is already filling leaves that capture
+        alone, since it is the acquisition you asked for.</p>
+      </item>
+      <item>
+        <p><gui>Search the buffer</gui> is at the foot of the same panel.</p>
+      </item>
+    </steps>
+
+    <figure>
+      <title>A held capture</title>
+      <desc><gui>event held</gui> in the status bar, the axis pinned to the event, and the
+      trigger marker at x = 0.</desc>
+      <media type="image" mime="image/png" src="figures/trigger-capture.png" width="1280" height="800">
+        <p>The pre-trigger share is drawn to the left of the marker.</p>
+      </media>
+    </figure>
+  </section>
+
+  <section id="shapes">
+    <title>The four shapes</title>
+    <terms>
+      <item>
+        <title>Edge</title>
+        <p>A crossing of the level in the chosen direction, the classic behaviour.</p>
+      </item>
+      <item>
+        <title>Pulse width</title>
+        <p>A crossing and its return, qualified by how long the excursion lasted: less than,
+        greater than, within or outside a pair of widths; the event is timed at the closing
+        edge.</p>
+      </item>
+      <item>
+        <title>Window</title>
+        <p>The signal entering or leaving a band between two levels; the panel keeps the two
+        levels at least one increment apart, because a zero-width band is not a band: the
+        condition becomes an exact float-equality test against the level, which an ordinary
+        signal never satisfies and a signal sitting at the level satisfies on every
+        transition.</p>
+      </item>
+      <item>
+        <title>Dropout</title>
+        <p>The absence of a crossing for longer than a timeout; one event per outage, re-arms
+        when a crossing returns.</p>
+      </item>
+    </terms>
+
+    <p>The shape's own rows are the only ones shown; the rest are hidden, so the panel never
+    offers a pulse width to a window trigger.</p>
+  </section>
+
+  <section id="multiple-events">
+    <title>Multiple events: keeping the last few acquisitions</title>
+    <p><gui>multiple events</gui> decides how many of the most recent triggered acquisitions stay on
+    screen at once. It is <em>1</em> by default, which is the event alone — the display you get
+    when you ask for no persistence — and it can be raised to 8. Each older acquisition is drawn
+    at half the brightness of the one before it (1, 0.5, 0.25, 0.125, …), and they are all aligned
+    on their own trigger edge, so the pre-trigger part of the event lines up from acquisition to
+    acquisition and whatever changes between them — jitter, ringing, the occasional glitch — shows
+    as a faint ghost behind the current trace. That is what a phosphor display does with
+    successive sweeps.</p>
+
+    <p>The older acquisitions are drawn <em>behind</em> the current one and nothing else changes
+    because of them: the axis still frames the event on screen, the trigger marker still marks
+    <em>its</em> edge, and the measurements still describe the current frame. Lowering
+    <gui>multiple events</gui> back to 1 remembers nothing and frees the retained acquisitions
+    immediately.</p>
+
+    <p>Two things bound how many are drawn, and the panel tells you when one of them bites.</p>
+    <list>
+      <item><p><em>Room in the plot.</em> Each older acquisition is an extra trace in the row that
+      plots its signal, so it needs a free trace slot there. A row holding four signals — the
+      layout the app starts with — has room for one older acquisition of each of them; a row per
+      signal has room for all seven.</p></item>
+      <item><p><em>Memory.</em> A retained acquisition is a whole window copied out of the ring,
+      so persistence may hold at most as much again as the buffer takes (see <cmd>--buffer-samples</cmd> and <cmd>--memory-limit-mb</cmd>).
+      On a long window at a high sample rate that bound is reached before the eighth layer.</p></item>
+    </list>
+  <section id="persistence">
+    <title>Persistence: how often the trace has been here</title>
+    <p><gui>persistence</gui> — the switch in the trigger panel's <gui>Advanced</gui> block — keeps
+    an <em>image</em> of the last acquisitions instead of their traces. Every acquisition is
+    accumulated into it, the one on screen included, so a cell's brightness means how many of them
+    passed through it: the sweep on screen is the brightest, the ones behind it add on top, and
+    where several agree the ink is brighter still. There is no stroke drawn over the image — the
+    acquisition on screen <em>is</em> its newest ink — so it fades with the rest in both modes. Each
+    signal is kept as its own image in that signal's own colour, so where two signals cross the same
+    place you see both, not one blended line. It is off by default.</p>
+
+    <p>Two things make it different from <gui>multiple events</gui> beside it, and the panel offers
+    both because they answer different questions. <em>It never runs out of room</em>: each signal's
+    image is sized to the plot on screen and capped, so a display of a thousand acquisitions costs
+    what a display of one costs — one image per signal, whatever the plot's trace slots, and a very
+    wide window does not make it grow — and there is no count to choose. <em>And it fades</em>, in
+    one of two ways — <gui>fades by</gui> picks them:</p>
+    <list>
+      <item><p><gui>acquisitions</gui>: every acquisition keeps
+      <gui>per acquisition</gui> of what was there before it (0.5, the default, is the schedule a
+      phosphor's afterglow has: 1, 0.5, 0.25, …). The display then shows the last few sweeps
+      whatever the trigger rate.</p></item>
+      <item><p><gui>time</gui>: the image fades by <gui>time constant s</gui> as the display runs —
+      one constant is the time for it to fall to a third of its ink — so a slow trigger leaves
+      faint sweeps and a fast one leaves bright ones, and the picture is the same whichever the
+      stream is doing.</p></item>
+    </list>
+
+    <p>Persistence is a <em>trigger mode</em> display, like the trigger itself: it is drawn while a
+    captured acquisition is on screen and goes away with the trigger, on a pause, and when you open
+    a stored waveform. Nothing about it moves the framing — the axis is still the current event's,
+    the older sweeps only add ink — and it reserves no space in the plot and cannot be clicked, so
+    it is never in the way of a cursor or a drop.</p>
+
+    <p>Both displays live in the trigger panel's <gui>Advanced</gui> block, together with the
+    trigger's other settings that are set up once and left alone.</p>
+  </section>
+
+
+    <p>If a depth cannot be shown in full, a notice says how many layers fit, and the panel's
+    tooltip carries the same rule. Persistence is a display of what has already been captured: it
+    changes neither what is acquired nor what is measured, and it does nothing while the trigger
+    is off.</p>
+  </section>
+
+  <section id="cache">
+    <title>The event cache, replay and compare</title>
+    <p><em>Every triggered acquisition is kept.</em> Latches are written to the event cache
+    (<file>~/.cache/udpscope/events/&lt;source&gt;/</file>) as a <file>.npy</file> of the
+    event, a <file>.txt</file> of what it was, and a <file>.bmp</file> picture drawn from the
+    samples. The <gui>Events</gui> block at the foot of the dock lists them, newest first, one
+    short row each: a marker for the event on screen, its title and its number. It is dimmed
+    until recording is on, an event is stored or one is being replayed. <gui>Manage</gui>
+    beside its heading opens the <gui>Events</gui> page over the plot, which keeps the last 32
+    (time, duration, signals, rate), each row with its own picture beside the numbers.</p>
+
+    <p>Clicking a row in the dock <em>replays</em> it: the stored event is loaded exactly like an exported
+    file, <em>without changing the layout</em> — the rows, the colours, the window, the
+    cursors and the measurements stay where they are and read the stored data instead. A
+    replay leaves trigger mode, because a file has no edge to wait for. <gui>Live</gui>, on the
+    <gui>Events</gui> page, goes back to the stream; the status bar names the file until
+    you do.</p>
+
+    <p>On the <gui>Events</gui> page, select two or more events in the list and the two buttons
+    under its header act on them:
+    <gui>Compare</gui> puts two events in two plots side by side, keeping the layout you have
+    — one plot per event, the axes synchronised, so zooming a row in one zooms the same row in
+    the other — and <gui>Accumulate</gui> overlays up to four of them in the same traces,
+    translucent, so where they agree the trace is brighter. Your own traces stay where they
+    are in both. They need events with the same signals and the same length. On this page a
+    single click selects and a <em>double</em> click replays.</p>
+
+    <p><gui>Record events</gui>, on the trigger page with the trigger's other options, is
+    what decides whether anything is kept. It is <em>off by default</em> — nothing is written
+    to disk until you ask — and with it off, and nothing stored, the dock's events block and
+    the page stay dimmed.</p>
+  </section>
+
+  <section id="search">
+    <title>Search the buffer</title>
+    <p><gui>Search the buffer</gui>, at the foot of the trigger panel and collapsed until you open
+    it, answers the question the trigger answers — <em>where does this condition hold?</em> — over
+    the <em>whole</em> retained buffer rather than at the live edge. It runs the trigger's own
+    evaluator over the ring in stream order, so a <gui>hit</gui> is not a level you point at: it is
+    an <em>instant</em> the trigger would have fired on, timed the way an acquisition would have
+    timed it. A pulse-width finding, for instance, is the closing edge of a qualifying excursion,
+    not the excursion itself.</p>
+
+    <p>The condition is the one the rest of the panel is set to — the same signal, shape, level and
+    options — so there is no second condition to keep in step: change the panel and the next search
+    asks the new question. Nothing is searched until you ask, and the status line says
+    <gui>not searched</gui>.</p>
+
+    <steps>
+      <item>
+        <p>Set the condition above, then press <gui>Search</gui>. Covering the whole ring takes a
+        moment, and the scan runs in chunks so the stream keeps arriving while it does; the status
+        line counts the ground covered — <gui>scanning 1.2 s of 8.0 s, 40 found</gui>.
+        <gui>Stop</gui> ends a scan early and keeps the hits found so far.</p>
+      </item>
+      <item>
+        <p>Step through the hits with the arrows either side of the position readout
+        (<gui>3 of 40</gui>). The first <gui>next</gui> goes to the first hit, and the ends do not
+        wrap — a wrap from the last hit to the first would look exactly like the view not having
+        moved. Each step <em>pauses</em> on its hit, centred, exactly as the Pause button does, so
+        what you read is the frozen window cut around that instant; press the pause button again to
+        go back to the stream.</p>
+      </item>
+      <item>
+        <p>Every plot row marks the hits that fall in the window, up to sixteen of them. When more
+        are in view the pane says so and suggests zooming in — <gui>16 of 38 marks shown — zoom in
+        to see the rest</gui> — and when the selected hit has scrolled off the window it says that
+        instead. A hit the live stream has since overwritten reads <gui>no longer in the buffer</gui>
+        beside its position.</p>
+      </item>
+    </steps>
+
+    <p>How a scan ended is part of the answer: <gui>N found in 8.0 s</gui> when it covered the whole
+    ring; <gui>N found; the stream overtook the oldest samples</gui> when the producer overwrote
+    samples before the scan reached them, so the count is of what was left; and
+    <gui>N found (the limit) in the newest …</gui> when a condition that holds almost everywhere —
+    an edge on a noisy signal — reached the ten-thousand-hit ceiling. The last is a stop, not a
+    crash: a hit list nobody could navigate is not worth building.</p>
+
+    <p>A result describes the ring it was taken from, so it is <em>dropped</em> when that ring is
+    replaced: a new <gui>CONFIG</gui> from the source, or a change to the signal set, re-describes
+    the stream and clears the hits. The condition above is untouched — only the answer to it
+    is.</p>
+  </section>
+
+  <section id="knowing">
+    <title>Worth knowing</title>
+    <list>
+      <item><p>Arming <em>enables</em> the signal if it was off, because a trigger on a signal
+      nobody acquires can never fire.</p></item>
+      <item><p>The pre-trigger share is a share of the <em>display window</em>, not of the
+      ring. A 2 s window at 50% captures 1 s before the edge and 1 s after.</p></item>
+      <item><p>There are four display states, and the status bar names each: <gui>armed</gui>
+      (watching, nothing drawn yet), <gui>capturing</gui> (the edge was accepted and the post
+      window is filling <em>in view</em>, with the marker at x = 0), <gui>event held</gui>
+      (the frozen capture) and <gui>disarmed</gui>. A held capture is never quietly replaced
+      by live data.</p></item>
+      <item><p>The first edge after arming is only accepted once the history reaches back a
+      full pre-trigger window, so a capture may legitimately be shorter than you asked for.
+      The axis is pinned to what the capture actually got. <gui>Force</gui> is the one
+      acquisition that skips that gate — it captures the history that exists, because "now"
+      is the whole of what you asked for — so on a ring that has just started filling its
+      left side is short even though the axis still shows only what it got.</p></item>
+      <item><p>Disarming <em>during</em> a capture publishes what the capture got to, so the
+      picture on screen at that moment stays on screen. No event fired, so the event count
+      does not move.</p></item>
+      <item><p>The trigger reads the <em>stored</em> signal — decimated and averaged — not the
+      wire signal. A spike narrower than one decimation group is filtered away rather than
+      triggering on data the buffer does not contain.</p></item>
+    </list>
+  </section>
+
+  <section id="example">
+    <title>Example</title>
+    <p>A 1 Hz sine, level 0, rising, 2 s window at 50%, Single. The capture spans
+    <code>[-1.000 .. 1.000]</code> with <code>n=20001</code> samples at 10 kS/s — the span
+    times the real rate, plus one — and the marker sits at x = 0 throughout.</p>
+  </section>
+
+</page>

help/C/org.udpscope.app/window.page

@@ -0,0 +1,65 @@
+<page xmlns="http://projectmallard.org/1.0/"
+      type="topic" style="task"
+      id="window">
+
+  <info>
+    <link type="guide" xref="index#viewing"/>
+    <link type="seealso" xref="navigate"/>
+    <desc>The time window control: how to set it, and why a long window is decimated rather
+    than refused.</desc>
+    <credit type="author copyright">
+      <name>Martino Ferrari</name>
+    </credit>
+  </info>
+
+  <title>Time window</title>
+
+  <p>The window is how much time the plot shows. Every row shares one window: the figure has
+  a single x link group, so the rows cannot drift apart. The trigger's event span follows it,
+  and the pre-trigger share is a share of <em>this</em> window.</p>
+
+  <section id="reach">
+    <title>How to reach it</title>
+    <steps>
+      <item>
+        <p>The header bar's window button opens a popover: type a number, pick a unit under
+        it, or step a decade with the arrows.</p>
+      </item>
+      <item>
+        <p>The button's own label is a reading of the current window in a natural unit,
+        width-locked so a change of window cannot widen the header bar.</p>
+      </item>
+    </steps>
+  </section>
+
+  <section id="knowing">
+    <title>Worth knowing</title>
+    <list>
+      <item><p>A window too long to store at the wire rate is <em>decimated, not refused</em>.
+      The shared clock takes a power-of-two stride, and each group of samples is
+      <em>averaged</em> rather than strided, so a tone above the stored Nyquist is attenuated
+      instead of aliasing to a false low frequency.</p></item>
+      <item><p>The stamp stored for a group is the group's <em>mean</em>, which is where the
+      averaging puts the value. Stamping at the end of a group would shift every trace half a
+      stored sample late.</p></item>
+      <item><p>Moving the window across a decimation boundary rebuilds the buffer and drops
+      the history. Walking it inside one decade is free.</p></item>
+      <item><p><em>This control is the only thing that changes the window.</em> A zoom, a pan
+      or a fit moves the view <em>inside</em> it and leaves it alone — which is the point of
+      the previous bullet: a wheel notch that redefined the window could re-plan the buffer
+      and throw your samples away.</p></item>
+      <item><p>The trigger sees the <em>stored</em> (filtered) signal, not the wire signal,
+      because an edge found on a sample that is not in the buffer could not be cut out of
+      it.</p></item>
+    </list>
+  </section>
+
+  <section id="example">
+    <title>Example</title>
+    <p>1 MS/s with the default buffer of 8 388 608 samples per signal (8.39 s). A 2 s window
+    stores every sample (<code>time x1</code>). Widen it to 600 s and the stride becomes
+    <code>x128</code>: 7.8 kS/s stored, anti-aliased at 3.9 kHz. A 5 kHz sine seen through that
+    window is attenuated by the filter, not folded down to a full-amplitude low-frequency one.</p>
+  </section>
+
+</page>

src/acquisition.cpp

@@ -3,9 +3,10 @@
 
 #include "acquisition.hpp"
 
-#include <udps_client.h>
+#include <limits>
 
 #include "layout_store.hpp"
+#include "source/registry.hpp"
 
 #include <glib/gstdio.h>
 
@@ -27,22 +28,6 @@ namespace {
 /// ring to make room for samples that are not coming.
 constexpr double kGlitchPackets = 256.0;
 
-SignalInfo to_info(const udps_signal_t& s) {
-  SignalInfo info;
-  info.name = s.name;
-  info.unit = s.unit;
-  info.type_code = s.type_code;
-  info.quant_type = s.quant_type;
-  info.rows = s.num_rows;
-  info.cols = s.num_cols;
-  info.range_min = s.range_min;
-  info.range_max = s.range_max;
-  info.time_mode = s.time_mode;
-  info.sampling_rate = s.sampling_rate;
-  info.time_signal_idx = s.time_signal_idx;
-  return info;
-}
-
 }  // namespace
 
 Acquisition::Acquisition(ScopeModel& model, const Config& cfg) : model_(model), cfg_(cfg) {}
@@ -50,25 +35,21 @@ Acquisition::Acquisition(ScopeModel& model, const Config& cfg) : model_(model),
 Acquisition::~Acquisition() { stop(); }
 
 void Acquisition::start() {
-  udps_client_config_t c;
-  udps_client_config_init(&c);
-  c.server_addr = cfg_.server.c_str();
-  c.server_port = cfg_.port;
-  c.multicast_group = cfg_.multicast.empty() ? nullptr : cfg_.multicast.c_str();
-  c.interface_addr = cfg_.interface_addr.empty() ? nullptr : cfg_.interface_addr.c_str();
-  c.recv_buffer_bytes = static_cast<std::uint32_t>(cfg_.recv_buffer_bytes);
-  c.silence_timeout_s = 2.0;
-  c.reconnect_delay_s = 0.5;
-  c.keepalive_interval_s = 1.0;
-
-  client_ = udps_client_create(&c);
-  if (client_ == nullptr) {
-    throw std::runtime_error("could not create the UDPS client for " + cfg_.server + ":" +
-                             std::to_string(cfg_.port));
+  // A started -- or *restarted* -- source is a new stream. Going live from a file view is the restart that
+  // matters: the store still holds the event's samples, and the new stream's clock can sit behind their
+  // stamps, so the guard below has to re-base rather than clamp. `ring=[2.5200..2.5200]` with `n` climbing
+  // was the symptom -- every packet pinned flat at the file view's last stamp.
+  model_.reset_stream();
+  last_stamp_ = -std::numeric_limits<double>::infinity();
+  if (!source_) {
+    SourceKind* kind = find_kind(cfg_.source_kind);
+    if (kind == nullptr) throw std::runtime_error("unknown source kind: " + cfg_.source_kind);
+    source_ = kind->make(cfg_.source_config());
   }
-  udps_client_set_callbacks(client_, &Acquisition::config_trampoline, &Acquisition::data_trampoline,
-                            &Acquisition::event_trampoline, this);
-  udps_client_set_datagram_cb(client_, &Acquisition::datagram_trampoline, this);
+  source_->set_datagram_tap([this](const std::uint8_t* bytes, std::size_t len, double recv_time) {
+    on_datagram(bytes, len, recv_time);
+  });
+  source_->open(*this);
   // `--capture-packets`: armed before the first datagram, so the first CONNECT and
   // its CONFIG -- the hardest strange behaviours to reproduce -- are in the ring.
   // The open itself still happens on the producer thread, at the first datagram.
@@ -82,35 +63,24 @@ void Acquisition::start() {
 }
 
 void Acquisition::stop() {
-  if (!running_.exchange(false, std::memory_order_acq_rel)) {
-    if (client_ != nullptr) {
-      udps_client_destroy(client_);
-      client_ = nullptr;
-    }
-    return;
-  }
-  if (thread_.joinable()) thread_.join();
-  if (client_ != nullptr) {
-    udps_client_destroy(client_);
-    client_ = nullptr;
-  }
+  if (running_.exchange(false, std::memory_order_acq_rel) && thread_.joinable()) thread_.join();
+  if (source_) source_->close();
 }
 
 void Acquisition::run() {
   while (running_.load(std::memory_order_acquire)) {
-    udps_client_poll(client_, 50);
-    udps_stats_t s;
-    udps_client_stats(client_, &s);
+    source_->poll(50);
+    const SourceStats s = source_->stats();
     StreamStats& out = model_.stats();
-    out.packets.store(s.packets_received, std::memory_order_relaxed);
-    out.frames.store(s.frames_delivered, std::memory_order_relaxed);
-    out.gaps.store(s.counter_gaps, std::memory_order_relaxed);
-    out.resequenced.store(s.late_resequenced, std::memory_order_relaxed);
-    out.late.store(s.late_delivered, std::memory_order_relaxed);
-    out.stale.store(s.stale_packets, std::memory_order_relaxed);
-    out.overflows.store(s.reorder_overflows, std::memory_order_relaxed);
+    out.packets.store(s.packets, std::memory_order_relaxed);
+    out.frames.store(s.frames, std::memory_order_relaxed);
+    out.gaps.store(s.gaps, std::memory_order_relaxed);
+    out.resequenced.store(s.resequenced, std::memory_order_relaxed);
+    out.late.store(s.late, std::memory_order_relaxed);
+    out.stale.store(s.stale, std::memory_order_relaxed);
+    out.overflows.store(s.overflows, std::memory_order_relaxed);
     out.reconnects.store(s.reconnects, std::memory_order_relaxed);
-    out.connected.store(udps_client_is_connected(client_) != 0, std::memory_order_relaxed);
+    out.connected.store(s.connected, std::memory_order_relaxed);
   }
 }
 
@@ -119,19 +89,25 @@ void Acquisition::set_capture_want(bool want, std::uint32_t slots) {
     if (slots > 0) capture_slots_ = slots;
     if (capture_path_.empty()) {
       // Keyed on the source: one path per source, the previous capture kept one deep.
-      std::string host = cfg_.server;
+      std::string host = cfg_.session_host();
       for (char& ch : host) {
         if (ch == ':' || ch == '/' || ch == ' ') ch = '_';
       }
-      std::string dir = cache_dir() + "/" + host + "-" + std::to_string(cfg_.port);
+      std::string dir = cache_dir() + "/" + host + "-" + std::to_string(cfg_.session_port());
       g_mkdir_with_parents(dir.c_str(), 0700);
       capture_path_ = dir + "/capture.bin";
       std::uint32_t addr = 0;
-      struct ::in_addr a;
-      if (::inet_pton(AF_INET, cfg_.server.c_str(), &a) == 1) {
-        addr = a.s_addr;  // already network order, which is what the header wants
+      std::uint16_t peer_port = 0;
+      if (cfg_.source_kind == "udps") {
+        // The source config, not cfg_.server/port: --source-opt overrides only the former.
+        const SourceConfig sc = cfg_.source_config();
+        struct ::in_addr a;
+        if (::inet_pton(AF_INET, sc.get("server", "127.0.0.1").c_str(), &a) == 1) {
+          addr = a.s_addr;  // already network order, which is what the header wants
+        }
+        peer_port = static_cast<std::uint16_t>(sc.get_int("port", 8000));
       }
-      capture_.set_peer(addr, cfg_.port);
+      capture_.set_peer(addr, peer_port);
     }
   }
   capture_want_.store(want, std::memory_order_release);
@@ -163,29 +139,20 @@ void Acquisition::on_datagram(const std::uint8_t* bytes, std::size_t len, double
   }
 }
 
-void Acquisition::datagram_trampoline(const std::uint8_t* bytes, std::size_t len,
-                                      double recv_time, void* user) {
-  static_cast<Acquisition*>(user)->on_datagram(bytes, len, recv_time);
-}
-
-void Acquisition::on_config(const udps_signal_t* signals, std::uint32_t count,
-                            std::uint8_t publish_mode) {
-  std::vector<SignalInfo> info;
-  info.reserve(count);
-  for (std::uint32_t i = 0; i < count; ++i) info.push_back(to_info(signals[i]));
-
+void Acquisition::on_config(const std::vector<SignalInfo>& info, std::uint8_t publish_mode) {
   // One line per CONFIG on stderr: what the stream says it is. This is the first
   // thing to look at when a signal refuses to plot.
   static const char* const kModes[] = {"strict", "accumulate", "decimate"};
-  std::fprintf(stderr, "[udpscope] CONFIG: %u signals, publish=%s\n", count,
+  std::fprintf(stderr, "[udpscope] CONFIG: %u signals, publish=%s\n",
+               static_cast<unsigned>(info.size()),
                publish_mode < 3 ? kModes[publish_mode] : "?");
   for (const SignalInfo& sig : info) {
     std::fprintf(stderr,
                  "[udpscope]   '%s' %ux%u (%u elem) rate=%g Hz time=%s idx=%u unit='%s'\n",
                  sig.name.c_str(), sig.rows, sig.cols, sig.elements(), sig.sampling_rate,
-                 sig.time_mode == UDPS_TIME_PACKET       ? "packet"
-                 : sig.time_mode == UDPS_TIME_FULL_ARRAY ? "full-array"
-                 : sig.time_mode == UDPS_TIME_FIRST_SAMPLE ? "first-sample"
+                 sig.time_mode == kTimePacket       ? "packet"
+                 : sig.time_mode == kTimeFullArray ? "full-array"
+                 : sig.time_mode == kTimeFirstSample ? "first-sample"
                                                            : "last-sample",
                  sig.time_signal_idx, sig.unit.c_str());
   }
@@ -195,22 +162,24 @@ void Acquisition::on_config(const udps_signal_t* signals, std::uint32_t count,
   // next session is the failure mode worth avoiding in a feature whose whole job is diagnosis.
   warned_batch_ = false;
   warned_outage_ = false;
+  warned_phantom_gap_ = false;
   warned_bridge_ = false;
   warned_time_source_ = false;
+  warned_clock_stall_ = false;
   // The clock choice is per connection too: a reconnect re-derives it from the frames
   // the new session actually delivers, rather than trusting a decision made about a
   // session that dropped.
   time_source_ = 0;
   reset_session_state();
   model_.stats().have_config.store(true, std::memory_order_relaxed);
-  model_.set_signals(std::move(info));
+  model_.set_signals(info);
 }
 
-void Acquisition::on_event(int event, const char* detail) {
+void Acquisition::on_event(SourceEvent event, const char* detail) {
   (void)detail;
-  if (event == UDPS_EVENT_CONNECTED) {
+  if (event == SourceEvent::Connected) {
     model_.stats().connected.store(true, std::memory_order_relaxed);
-  } else if (event == UDPS_EVENT_DISCONNECTED) {
+  } else if (event == SourceEvent::Disconnected) {
     model_.stats().connected.store(false, std::memory_order_relaxed);
     // The session dropped mid-flight: everything the producer knows about *that*
     // session's numbering and clocks is now a lie about the next one. Clearing it here
@@ -235,21 +204,75 @@ void Acquisition::reset_session_state() noexcept {
   have_arrival_interval_ = false;
   arrival_interval_ = 0.0;
   arrival_prev_ = 0.0;
+  have_prev_frame_recv_ = false;
+  prev_frame_recv_ = 0.0;
+  // The clock origin is adopted again: the next session's first stamp is that session's epoch.
+  epoch_adopted_ = false;
 }
 
-std::uint32_t Acquisition::build_stamps(const udps_frame_t* frame, int time_signal) {
+void Acquisition::note_frame_arrival(double recv_time) noexcept {
+  const bool first = !have_prev_frame_recv_;
+  const double elapsed = first ? 0.0 : recv_time - prev_frame_recv_;
+  prev_frame_recv_ = recv_time;
+  have_prev_frame_recv_ = true;
+  // The arrival *cadence* belongs to the arrival clock, and `build_stamps()`'s arrival branch keeps
+  // it whenever that clock is the one in play (`time_source_ == 2`, decided once per connection and
+  // sticky). Every other case needs it here: relative mode returns before that branch, and a stream
+  // whose declared time signal checks out never reaches it either -- while the reservation test
+  // below weighs the counter's claim against a measured cadence whatever clock the display uses,
+  // because a counter that does not count packets lies in all of them. The two writers are therefore
+  // exclusive by `time_source_`, and this is the branch's own update (0.8/0.2) so the estimate does
+  // not jump at the one frame where the clock changes hands.
+  if (first || time_source_ == 2) return;
+  if (elapsed > 0.0 && std::isfinite(elapsed)) {
+    arrival_interval_ =
+        have_arrival_interval_ ? 0.8 * arrival_interval_ + 0.2 * elapsed : elapsed;
+    have_arrival_interval_ = true;
+  }
+}
+
+bool Acquisition::gap_plausible(std::uint32_t missing, double elapsed, const Partition& part,
+                                u64 g) const {
+  if (missing == 0) return true;
+  // The ring cannot hold a hole bigger than itself, and this test needs no measurement: the
+  // invariant's own rule is that the reservation's *sample* cost -- `missing * batch_`, not the
+  // packet cap -- is what has to be weighed against the ring. A hole that laps the ring erases the
+  // history it is meant to annotate, can never be backfilled (its slots are already overwritten),
+  // and is never forgotten (`forget_holes_before()` waits for slots the ring has passed), so it
+  // leaves a band over a buffer that is all NaN.
+  if (g == 0 || part.time_capacity == 0) return false;
+  if (u64(missing) * u64(batch_) / g >= part.time_capacity) return false;
+  // And the counter has to agree with the wire about how long the loss took. The counter is a claim
+  // about the stream; the arrival clock is a *measurement* of it: `missing` packets would have taken
+  // `missing` frame intervals to arrive, and the frame before this one is the witness of how long
+  // actually passed. A device whose counter counts samples, or frames of an inner layer, reports a
+  // forward jump on *every* datagram while the wire delivers on time -- and believing that booked a
+  // NaN hole per packet, i.e. a band over the whole window filled with samples that were never
+  // missing, which no backfill can repair because no packet was ever lost. The factor is a half and
+  // not one: the socket clock jitters and a drain can compress two frames' arrival times, so only a
+  // claim the wire flatly contradicts (half the time it needs, or less) is refused. A refused gap
+  // costs a shading, never data.
+  if (have_arrival_interval_ && arrival_interval_ > 0.0 && elapsed > 0.0 &&
+      elapsed < 0.5 * double(missing) * arrival_interval_) {
+    return false;
+  }
+  return true;
+}
+
+std::uint32_t Acquisition::build_stamps(const Frame& frame, int time_signal,
+                                        bool counter_gap_refused) {
   // The frame's span in base ticks: a scalar signal carries `num_samples` values
   // (one per batched cycle), a block signal (rows*cols > 1) carries its whole
   // element block. The largest of those is how many base ticks this frame spans --
   // in `strict` mode `num_samples` is 1 while a 1x1000 block carries 1000 samples.
-  std::uint32_t n = frame->num_samples;
-  for (std::uint32_t i = 0; i < frame->num_signals; ++i) {
-    n = std::max(n, udps_signal_num_elements(&frame->signals[i]));
+  std::uint32_t n = frame.num_samples;
+  for (std::uint32_t i = 0; i < frame.num_signals; ++i) {
+    n = std::max(n, frame.signals[i].elements());
   }
   stamps_.assign(n, 0.0);
   abs_stamps_.assign(n, 0.0);
 
-  // Samples per packet, needed in both modes: relative stamping must advance `slot_base_`
+  // Samples per packet, needed in both modes: relative stamping must advance its own clock
   // past the reserved hole before placing this frame's own stamps, and `on_data` must size
   // the hole before calling this function -- both operations require knowing how many samples
   // a missing packet represents, which is only knowable from the first frame that arrives.
@@ -277,35 +300,43 @@ std::uint32_t Acquisition::build_stamps(const udps_frame_t* frame, int time_sign
     }
   }
 
-  // Relative mode: the stamp is a pure function of position and the *declared* rate. Nothing
-  // below this block runs -- not the arrival-cadence override, not the degeneracy guard, not
-  // the glitch bridge, not the monotonic clamp's reason for existing -- because a position
-  // cannot jitter, cannot fail to advance and cannot jump.
+  // Relative mode: the stamp is the *declared* interval counted from the stream's own origin.
+  // Nothing below this block runs -- not the arrival-cadence override, not the degeneracy guard,
+  // not the glitch bridge, not the monotonic clamp's reason for existing -- because a counted
+  // clock cannot jitter, cannot fail to advance and cannot jump.
+  //
+  // The clock is **accumulated in seconds**, never recomputed as `position * interval`: see
+  // `Acquisition::rel_base_s_` for the defect that distinction cost. The interval is read from the
+  // plan, which is the stream's declared rate as soon as a streamed channel exists -- and
+  // `on_data` refuses a frame until one does, so the fallback interval can never be the origin.
   if (cfg_.relative_time) {
     double dt = model_.partition().base_dt;
     if (!(dt > 0.0)) dt = 1.0e-3;
-    // The reserved hole for the missing packets advances `slot_base_` so this frame's
-    // own stamps land *after* the hole rather than on top of it. The same conditions
-    // the reservation call uses: not late, gap present, batch known, within the cap.
-    if (!frame->late && frame->lost > 0 && batch_ > 0 &&
-        double(frame->lost) <= kGlitchPackets) {
-      slot_base_ += u64(frame->lost) * batch_;
+    // The reserved hole for the missing packets advances the clock so this frame's own stamps land
+    // *after* the hole rather than on top of it. The same conditions the reservation call uses: not
+    // late, gap present, batch known, within the cap -- and not one the arrival clock or the ring
+    // refused, because the advance and the reservation are the *same* claim about the wire:
+    // believing a phantom gap here would stretch the timeline by exactly the loss that did not
+    // happen.
+    if (!frame.late && frame.lost > 0 && batch_ > 0 && !counter_gap_refused &&
+        double(frame.lost) <= kGlitchPackets) {
+      rel_base_s_ += double(frame.lost) * double(batch_) * dt;
     }
     for (std::uint32_t k = 0; k < n; ++k) {
-      stamps_[k] = double(slot_base_ + k) * dt;
+      stamps_[k] = rel_base_s_ + double(k) * dt;
     }
-    slot_base_ += n;
+    rel_base_s_ += double(n) * dt;
     // The absolute clock is still read, for export only. When the stream carries no usable
     // time signal there is no absolute clock to record and the relative stamp is the honest
     // answer -- an export then says what the counter says, which is all anyone had.
-    if (time_signal >= 0 && time_signal < static_cast<int>(frame->num_signals)) {
-      const udps_signal_t& ts = frame->signals[time_signal];
-      const bool scalar_time = udps_signal_num_elements(&ts) == 1;
+    if (time_signal >= 0 && time_signal < static_cast<int>(frame.num_signals)) {
+      const SignalInfo& ts = frame.signals[time_signal];
+      const bool scalar_time = ts.elements() == 1;
       for (std::uint32_t k = 0; k < n; ++k) {
         abs_stamps_[k] =
             scalar_time
-                ? udps_frame_value(frame, static_cast<std::uint32_t>(time_signal), k, 0)
-                : udps_frame_value(frame, static_cast<std::uint32_t>(time_signal), 0, k);
+                ? frame.value(static_cast<std::uint32_t>(time_signal), k, 0)
+                : frame.value(static_cast<std::uint32_t>(time_signal), 0, k);
       }
     } else {
       for (std::uint32_t k = 0; k < n; ++k) abs_stamps_[k] = stamps_[k];
@@ -339,27 +370,27 @@ std::uint32_t Acquisition::build_stamps(const udps_frame_t* frame, int time_sign
   // arrival clock for the rest of its life (until a CONFIG says otherwise): letting
   // the decision flip per frame is what interleaved two timelines in one ring.
   if (time_source_ != 2 && time_signal >= 0 &&
-      time_signal < static_cast<int>(frame->num_signals)) {
-    const udps_signal_t& ts = frame->signals[time_signal];
-    // How the client indexes a signal's values depends on its shape
-    // (`udps_frame_value`): a scalar carries one value per batched cycle, so the
+      time_signal < static_cast<int>(frame.num_signals)) {
+    const SignalInfo& ts = frame.signals[time_signal];
+    // How a frame indexes a signal's values depends on its shape
+    // (`Frame::value`): a scalar carries one value per batched cycle, so the
     // stamp of sample k is (sample=k, elem=0); a multi-element signal carries one
     // *sample* of `elements` values per packet, so the stamp of sample k is
     // (sample=0, elem=k). Passing the scalar form for both is why FULL_ARRAY time
     // signals -- the only mode that carries a stamp per element -- read as
     // element 0 for every sample and were then judged degenerate.
-    const bool scalar_time = udps_signal_num_elements(&ts) == 1;
+    const bool scalar_time = ts.elements() == 1;
     auto value_of = [&](std::uint32_t k) {
       return scalar_time
-                 ? udps_frame_value(frame, static_cast<std::uint32_t>(time_signal), k, 0)
-                 : udps_frame_value(frame, static_cast<std::uint32_t>(time_signal), 0, k);
+                 ? frame.value(static_cast<std::uint32_t>(time_signal), k, 0)
+                 : frame.value(static_cast<std::uint32_t>(time_signal), 0, k);
     };
     switch (ts.time_mode) {
-      case UDPS_TIME_FULL_ARRAY:
+      case kTimeFullArray:
         for (std::uint32_t k = 0; k < n; ++k) stamps_[k] = value_of(k);
         used_stream_time = true;
         break;
-      case UDPS_TIME_FIRST_SAMPLE: {
+      case kTimeFirstSample: {
         // Only element 0 is meaningful here: the producer stamps the batch's first
         // sample and says nothing about the rest, so the cadence has to space them --
         // exactly as LAST_SAMPLE below dates its batch backwards from its anchor.
@@ -373,7 +404,7 @@ std::uint32_t Acquisition::build_stamps(const udps_frame_t* frame, int time_sign
         used_stream_time = true;
         break;
       }
-      case UDPS_TIME_LAST_SAMPLE: {
+      case kTimeLastSample: {
         const double anchor = value_of(n > 0 ? n - 1 : 0);
         for (std::uint32_t k = 0; k < n; ++k)
           stamps_[k] = anchor - double(n - 1 - k) * cadence;
@@ -477,7 +508,7 @@ std::uint32_t Acquisition::build_stamps(const udps_frame_t* frame, int time_sign
     // was produced, and the earlier ones are dated backwards. A gap (`lost`)
     // shows up as extra elapsed time between arrivals, which is exactly the
     // spacing the samples had.
-    const double end = frame->recv_time;
+    const double end = frame.recv_time;
     if (!have_arrival_epoch_) {
       arrival_epoch_ = end;
       have_arrival_epoch_ = true;
@@ -533,7 +564,7 @@ std::uint32_t Acquisition::build_stamps(const udps_frame_t* frame, int time_sign
     // to a dead clock; they do not, and the wipe is what made a single glitching packet
     // look like the stream restarting from zero.
     time_source_ = 2;
-    const double end = frame->recv_time;
+    const double end = frame.recv_time;
     arrival_epoch_ = end - (last_stamp_ + model_.epoch());
     arrival_prev_ = end;
   }
@@ -553,7 +584,7 @@ std::uint32_t Acquisition::build_stamps(const udps_frame_t* frame, int time_sign
   return n;
 }
 
-void Acquisition::on_data(const udps_frame_t* frame) {
+void Acquisition::on_data(const Frame& frame) {
 
   std::lock_guard<std::mutex> lock(model_.mutex());
   if (!running_.load(std::memory_order_relaxed)) return;
@@ -561,14 +592,30 @@ void Acquisition::on_data(const udps_frame_t* frame) {
   // The counter is this frame's identity and the hole's address. A *late* frame's counter is
   // behind the sequence, so it must not move the mark -- the hole it belongs in was addressed
   // from the counter that revealed it.
-  if (!have_counter_ || static_cast<std::int32_t>(frame->counter - last_counter_) > 0) {
-    last_counter_ = frame->counter;
+  if (!have_counter_ || static_cast<std::int32_t>(frame.counter - last_counter_) > 0) {
+    last_counter_ = frame.counter;
     have_counter_ = true;
   }
 
   const Partition& part = model_.partition();
   const std::vector<ChannelInfo>& channels = model_.channels();
-  if (part.time_capacity == 0 || channels.empty()) return;
+  // A frame is only stored into a model that has a **streamed** channel. A model holding only
+  // *derived* ones -- a session's math channels, applied before the stream's own have arrived, or
+  // a file's channels while the math is re-applied -- has nowhere to put a streamed sample, and its
+  // plan is built from the 1 kHz fallback interval, which is **not the stream's rate**. Accepting
+  // such a frame (which the `channels.empty()` test below did) stamps the timeline at that fallback,
+  // and the frame after the stream's own channels arrive makes every later stamp *behind* the one
+  // already written -- the monotonic clamp holds the clock there for the rest of the run, the
+  // trigger's `history` never fills and the plot draws nothing. The reading is the `trig engine:`
+  // line: `n` climbing while `ring=[a..a]` stands still.
+  bool streamed = false;
+  for (const ChannelInfo& c : channels) {
+    if (!c.math) {
+      streamed = true;
+      break;
+    }
+  }
+  if (part.time_capacity == 0 || channels.empty() || !streamed) return;
 
   // A frame delivered behind the sequence: the slots it owns were reserved as NaN by
   // `reserve_hole()`, so it writes values into them and does nothing else. It is deliberately
@@ -580,7 +627,7 @@ void Acquisition::on_data(const udps_frame_t* frame) {
   // Placed here and not earlier because `part`/`channels` are not in scope above, and not
   // later because `build_stamps()` is stateful: a late frame's stamps would walk the clock
   // backwards and can throw the whole stream onto the arrival clock.
-  if (frame->late) {
+  if (frame.late) {
     backfill_from(frame, part, channels, model_.live(), part.time_stride);
     return;
   }
@@ -600,20 +647,40 @@ void Acquisition::on_data(const udps_frame_t* frame) {
     // (full-array, more than one element, no declared rate).
     for (std::size_t i = 0; i < model_.signals().size(); ++i) {
       const SignalInfo& sig = model_.signals()[i];
-      if (sig.time_mode == UDPS_TIME_FULL_ARRAY && sig.elements() > 1 &&
+      if (sig.time_mode == kTimeFullArray && sig.elements() > 1 &&
           sig.sampling_rate == 0.0) {
         time_signal = static_cast<int>(i);
         break;
       }
     }
   }
-  const std::uint32_t n = build_stamps(frame, time_signal);
+  // The wire's own cadence, and the verdict on the counter's claim, both taken *before* the
+  // stamps: relative mode's clock advance and the reservation below are the same claim
+  // about the wire (see `build_stamps`), so they have to agree about it. The verdict is taken
+  // before the cadence is updated, too: folding this frame's own arrival into the estimate would
+  // let one burst raise the very number that is supposed to corroborate it -- a 200-packet outage
+  // smooths the interval to 40 ms and then refuses itself.
+  const bool first_frame = !have_prev_frame_recv_;
+  const double since_prev = first_frame ? 0.0 : frame.recv_time - prev_frame_recv_;
+  const std::uint32_t missing = frame.lost;
+  const bool gap_refused =
+      missing > 0 && !gap_plausible(missing, since_prev, part, part.time_stride);
+  note_frame_arrival(frame.recv_time);
+
+  const std::uint32_t n = build_stamps(frame, time_signal, gap_refused);
   if (n == 0) return;
 
-  if (model_.epoch() == 0.0) {
+  // The epoch -- the stream time the display's x = 0 means -- is the first frame's stamp, adopted
+  // **once per connection**. The test is a state and not a value: relative mode's first frame is
+  // stamped exactly 0, so an `epoch() == 0.0` test reads that as "no epoch yet" and lets the
+  // *second* frame move the origin, which stalls the timeline through that frame (the samples of
+  // one frame all land on one stamp) and shifts every later x by a frame's span. The flag is
+  // re-armed by `reset_session_state()`, because a new session's clock is a new clock.
+  if (!epoch_adopted_) {
+    epoch_adopted_ = true;
     model_.set_epoch_if_unset(stamps_[0]);
     std::fprintf(stderr, "[udpscope] time base: epoch=%.3f, first frame recv=%.3f, n=%u\n",
-                 model_.epoch(), frame->recv_time, n);
+                 model_.epoch(), frame.recv_time, n);
     std::fflush(stderr);
   }
   const double epoch = model_.epoch();
@@ -640,7 +707,7 @@ void Acquisition::on_data(const udps_frame_t* frame) {
   // The generation is the signal rather than the stride/channel-count comparison below: only
   // a CONFIG that *changes* the stream re-plans the store -- a reconnect's identical CONFIG
   // keeps it, history and all (see `ScopeModel::set_signals`).
-  // `slot_base_` is deliberately *not* reset -- it is relative mode's clock origin, samples
+  // `rel_base_s_` is deliberately *not* reset -- it is relative mode's clock origin, seconds
   // since the stream began, and relative time must not jump backwards when the user retypes
   // the window.
   if (const unsigned gen = model_.plan_generation(); gen != seen_plan_generation_) {
@@ -687,8 +754,29 @@ void Acquisition::on_data(const udps_frame_t* frame) {
   // through the same decimation accumulators (value_acc_, value_acc_n_, math_sample_),
   // which must already be sized to the current channel count and stride before any
   // per-sample write.
-  const std::uint32_t missing = frame->lost;
-  if (missing > 0 && batch_ > 0 && double(missing) <= kGlitchPackets) {
+  if (missing > 0 && gap_refused) {
+    // A claim the wire contradicted, or a hole the ring cannot hold: framing it as NaN is what
+    // turns one phantom gap into a band over the whole window (and, at a batch big enough, into
+    // minutes of the producer's time under this lock). The samples are kept, no hole is booked,
+    // and the timeline above was not advanced either -- so the picture shows the data and the gap
+    // shows as the x discontinuity it is. Said once per connection with the numbers, because it is
+    // otherwise invisible: the status bar's `gaps` climbs either way.
+    model_.stats().gaps_refused.fetch_add(1, std::memory_order_relaxed);
+    if (!warned_phantom_gap_) {
+      warned_phantom_gap_ = true;
+      std::fprintf(stderr,
+                   "[udpscope] warning: the counter reports %u packet(s) missing (%llu samples, "
+                   "%.3f s at the measured cadence of %.6f s/frame) but only %.3f s passed since "
+                   "the previous frame, or the hole is larger than the ring (%llu slots); "
+                   "refusing the reservation and keeping the samples. A counter that does not "
+                   "count packets -- samples, or frames of an inner layer -- reports a jump on "
+                   "every datagram and reads exactly like this.\n",
+                   missing, static_cast<unsigned long long>(std::uint64_t(missing) * batch_),
+                   double(missing) * arrival_interval_, arrival_interval_, since_prev,
+                   static_cast<unsigned long long>(u64(missing) * u64(batch_) / part.time_stride));
+      std::fflush(stderr);
+    }
+  } else if (missing > 0 && batch_ > 0 && double(missing) <= kGlitchPackets) {
     reserve_hole(missing, part, channels, store, g);
   } else if (missing > 0 && !warned_outage_) {
     warned_outage_ = true;
@@ -801,13 +889,36 @@ void Acquisition::on_data(const udps_frame_t* frame) {
                  edge, last_stamp_, span - post_s, post_s, snap ? snap->pre_s : 0.0,
                  snap ? snap->post_s : 0.0,
                  static_cast<unsigned long long>(snap ? snap->stamps.size() : 0),
-                 frame->recv_time, static_cast<unsigned long long>(tick_),
+                 frame.recv_time, static_cast<unsigned long long>(tick_),
                  std::chrono::duration<double>(std::chrono::steady_clock::now() - started_)
                      .count());
     std::fflush(stderr);
     if (tc.mode == TriggerMode::Single) tc.armed = false;
   };
 
+  // The monotonic clamp, and the one state it must not be allowed to sit in. `max()` is for a
+  // stream clock that glitches, fails to advance for a sample or arrives out of order -- one
+  // sample, or a few, held back. A **whole frame** whose stamps are all behind the clock is not
+  // that: the timeline has stopped while the wire has not, and nothing downstream can recover. It
+  // is staged as a reading because the picture it produces is a *blank* plot beside a healthy
+  // status bar, which names no cause at all: the trigger's `history` never reaches its pre-window,
+  // so it never latches and the display sits in `Waiting`; the renderer's bound window is empty, so
+  // nothing is drawn even with the trigger off. `relative_time` with a session's math channel was
+  // how this was reached (see `rel_base_s_`); the guard is `build_stamps`' own accumulator.
+  if (!warned_clock_stall_ && n > 0 && stamps_[0] - epoch < last_stamp_ &&
+      stamps_[n - 1] - epoch < last_stamp_) {
+    warned_clock_stall_ = true;
+    const u64 held = model_.live().time().size();
+    std::fprintf(stderr,
+                 "[udpscope] warning: the clock stalled at %.6f s: %u samples stamped [%.6f..%.6f] s "
+                 "are all behind it, so the timeline stands still while frames keep arriving -- "
+                 "nothing can be drawn and no trigger can latch. The plan's interval is %.9g s now; "
+                 "ring n=%llu\n",
+                 last_stamp_, n, stamps_[0] - epoch, stamps_[n - 1] - epoch, part.base_dt,
+                 static_cast<unsigned long long>(held));
+    std::fflush(stderr);
+  }
+
   for (std::uint32_t k = 0; k < n; ++k) {
     const u64 tick = tick_++;
     // The shared clock's group boundary, read once and reused by the time ring, the channel
@@ -860,9 +971,9 @@ void Acquisition::on_data(const udps_frame_t* frame) {
       // the cycle's sample at element `k`. Either way element 0 is the channel.
       const double raw =
           ch.elements > 1
-              ? udps_frame_value(frame, static_cast<std::uint32_t>(ch.signal), 0,
-                                 std::min<std::uint32_t>(k, ch.elements - 1))
-              : udps_frame_value(frame, static_cast<std::uint32_t>(ch.signal), k, 0);
+              ? frame.value(static_cast<std::uint32_t>(ch.signal), 0,
+                            std::min<std::uint32_t>(k, ch.elements - 1))
+              : frame.value(static_cast<std::uint32_t>(ch.signal), k, 0);
       // Every sample is read and accumulated even when only one in `period` is stored:
       // that is the whole point of the filter. Skipping the read -- which is what the
       // old stride did -- is what made decimation alias.
@@ -899,6 +1010,38 @@ void Acquisition::on_data(const udps_frame_t* frame) {
   }
   last_stamp_ = last_stamp_used;
 
+  // A Force pressed since the last packet: one acquisition, at the present moment, without waiting
+  // for the condition to hold. Read *here* -- the end of the packet, past the channel loop -- for
+  // the reason the latch itself is deferred out of that loop: `last_stamp_` is the newest stored
+  // sample by now, so the capture opens on the moment the user pressed, and every channel has
+  // pushed that sample, so the cut the latch goes on to make cannot clamp it away
+  // (`publish_event()` clamps to each value ring's `produced()`).
+  //
+  // It opens the capture and nothing else. The latch below -- reached through `engine.process()`
+  // by an edge, through `engine.force()` here -- is what cuts the window, bumps the latch count,
+  // sets the trigger time and applies the mode's re-arm rule, so a forced acquisition is framed,
+  // pinned and recorded exactly like one the condition produced. A capture already in flight is
+  // not cancelled: it *is* the acquisition being asked for, and the engine refuses the request
+  // rather than restarting it.
+  if (force_want_.exchange(false, std::memory_order_acq_rel)) {
+    if (engine.force(last_stamp_)) {
+      std::fprintf(stderr,
+                   "[udpscope] trigger: forced acquisition, edge at %.3f s -- want "
+                   "[-%.4f..%.4f] s, %.4f s of history behind it, mode=%s\n",
+                   last_stamp_, event_span - post_want, post_want, last_stamp_ - oldest_s,
+                   tc.mode == TriggerMode::Single ? "single (disarms at the latch)" : "normal");
+      std::fflush(stderr);
+    } else {
+      // Nothing to force. Every cause is a state the user can see from the panel -- a trigger that
+      // is off, a signal that is not acquired, the engine disarmed, a capture already filling --
+      // so it is named on stderr rather than swallowed.
+      std::fprintf(stderr,
+                   "[udpscope] trigger: force ignored (enabled=%d armed=%d ch=%d pending=%d)\n",
+                   int(tc.enabled), int(engine.armed()), trig_channel, int(engine.pending()));
+      std::fflush(stderr);
+    }
+  }
+
   model_.trigger_armed().store(engine.armed(), std::memory_order_relaxed);
   // The edge goes out before the flag that makes the UI read it (release/acquire on
   // `trigger_pending`), so a tick that sees a capture open sees which edge it is for. A
@@ -907,7 +1050,7 @@ void Acquisition::on_data(const udps_frame_t* frame) {
   if (engine.pending()) model_.set_capture_edge(engine.last_trigger_time());
   model_.set_trigger_pending(engine.pending());
   static std::int64_t next_engine_log = 0;
-  const std::int64_t now_e = static_cast<std::int64_t>(frame->recv_time * 1.0e6);
+  const std::int64_t now_e = static_cast<std::int64_t>(frame.recv_time * 1.0e6);
   if (now_e >= next_engine_log) {
     next_engine_log = now_e + 1000000;
     // `elapsed/post_want` is the capture's progress in the only unit that matters now
@@ -917,12 +1060,20 @@ void Acquisition::on_data(const udps_frame_t* frame) {
     std::fprintf(stderr,
                  "[udpscope] trig engine: ch=%d armed=%d pending=%d elapsed=%.4f/%.4f s "
                  "accum=%llu history=%.4f/%.4f s pre_pct=%.0f v=%.4g now_t=%.3f "
-                 "holdoff_until=%.3f\n",
+                 "holdoff_until=%.3f ring=[%.4f..%.4f] n=%zu\n",
                  trig_channel, int(engine.armed()), int(engine.pending()),
                  engine.post_elapsed(), engine.post_seconds(),
                  static_cast<unsigned long long>(engine.post_accum()), engine.history(),
                  engine.pre_seconds(), tc.pretrigger_pct, engine.last_value(),
-                 engine.last_t(), engine.holdoff_until());
+                 engine.last_t(), engine.holdoff_until(),
+                 // The store's own retained span, beside the engine's view of the clock. Going live
+                 // restarts the client, and the question a stalled display raises is whether the *time
+                 // ring* is moving at all: `n` climbing while `ring` stands still is a clock problem, and
+                 // `ring` moving while `now_t` does not is a feed problem. Neither can be told from the
+                 // engine's own fields.
+                 store.time().size() > 0 ? double(store.time()[0]) : 0.0,
+                 store.time().size() > 0 ? double(store.time()[store.time().size() - 1]) : 0.0,
+                 store.time().size());
     std::fflush(stderr);
   }
 }
@@ -1004,7 +1155,7 @@ void Acquisition::reserve_hole(std::uint32_t missing, const Partition& part,
   model_.stats().hole_slots.fetch_add(h.slot_count, std::memory_order_relaxed);
 }
 
-void Acquisition::backfill_from(const udps_frame_t* frame, const Partition& part,
+void Acquisition::backfill_from(const Frame& frame, const Partition& part,
                                 const std::vector<ChannelInfo>& channels, BufferStore& store,
                                 u64 g) {
   // `batch_` is learned in `build_stamps()`, which a late frame never reaches. A late frame
@@ -1021,7 +1172,7 @@ void Acquisition::backfill_from(const udps_frame_t* frame, const Partition& part
   // late packets would be dropped on the next line.
   Hole* hole = nullptr;
   for (Hole& h : model_.holes()) {
-    const std::int32_t into = static_cast<std::int32_t>(frame->counter - h.counter_first);
+    const std::int32_t into = static_cast<std::int32_t>(frame.counter - h.counter_first);
     if (into >= 0 && into < static_cast<std::int32_t>(h.packets)) {
       hole = &h;
       break;
@@ -1032,7 +1183,7 @@ void Acquisition::backfill_from(const udps_frame_t* frame, const Partition& part
   // The packet's own span in absolute base ticks. `tick_begin` is the hole's first raw sample
   // and the packets inside a hole are consecutive, so the counter's distance from
   // `counter_first` places this one exactly.
-  const u64 lo = hole->tick_begin + u64(frame->counter - hole->counter_first) * u64(batch_);
+  const u64 lo = hole->tick_begin + u64(frame.counter - hole->counter_first) * u64(batch_);
   const u64 hi = lo + u64(batch_);
 
   u64 filled = 0;
@@ -1056,11 +1207,11 @@ void Acquisition::backfill_from(const udps_frame_t* frame, const Partition& part
         const u64 k = s * period + j - lo;  // this packet's own sample index, 0..batch_-1
         const double raw =
             channels[i].elements > 1
-                ? udps_frame_value(frame, static_cast<std::uint32_t>(channels[i].signal), 0,
-                                   std::min<std::uint32_t>(static_cast<std::uint32_t>(k),
-                                                           channels[i].elements - 1))
-                : udps_frame_value(frame, static_cast<std::uint32_t>(channels[i].signal),
-                                   static_cast<std::uint32_t>(k), 0);
+                ? frame.value(static_cast<std::uint32_t>(channels[i].signal), 0,
+                              std::min<std::uint32_t>(static_cast<std::uint32_t>(k),
+                                                      channels[i].elements - 1))
+                : frame.value(static_cast<std::uint32_t>(channels[i].signal),
+                              static_cast<std::uint32_t>(k), 0);
         acc += raw * channels[i].gain + channels[i].offset;
       }
       const f32 value = static_cast<f32>(acc / double(period));
@@ -1082,18 +1233,4 @@ void Acquisition::backfill_from(const udps_frame_t* frame, const Partition& part
   model_.stats().backfilled.fetch_add(filled, std::memory_order_relaxed);
 }
 
-// Static trampolines: the client's C ABI cannot call a member function directly.
-void Acquisition::config_trampoline(const udps_signal_t* signals, std::uint32_t count,
-                                    std::uint8_t publish_mode, void* user) {
-  static_cast<Acquisition*>(user)->on_config(signals, count, publish_mode);
-}
-
-void Acquisition::data_trampoline(const udps_frame_t* frame, void* user) {
-  static_cast<Acquisition*>(user)->on_data(frame);
-}
-
-void Acquisition::event_trampoline(udps_event_t event, const char* detail, void* user) {
-  static_cast<Acquisition*>(user)->on_event(static_cast<int>(event), detail);
-}
-
 }  // namespace udpscope

src/acquisition.hpp

@@ -8,21 +8,22 @@
 #include "model.hpp"
 #include "trigger.hpp"
 
-#include <udps_client.h>
+#include "source/data_source.hpp"
 
 #include <atomic>
 #include <chrono>
 #include <cstdint>
 #include <limits>
+#include <memory>
 #include <thread>
 #include <vector>
 
 namespace udpscope {
 
-/// Owns the UDPStreamer client and the producer thread that feeds the model's
+/// Owns the data source and the producer thread that feeds the model's
 /// acquisition buffer. Everything it touches from the thread is serialised on
 /// `ScopeModel::mutex()`, so a UI-side structural change cannot race a frame.
-class Acquisition {
+class Acquisition : private SourceSink {
  public:
   Acquisition(ScopeModel& model, const Config& cfg);
   ~Acquisition();
@@ -30,8 +31,8 @@ class Acquisition {
   Acquisition(const Acquisition&) = delete;
   Acquisition& operator=(const Acquisition&) = delete;
 
-  /// Opens the client (no socket until the first poll) and starts the thread.
-  /// Throws std::runtime_error when the client cannot be created.
+  /// Opens the source (no socket until the first poll) and starts the thread.
+  /// Throws std::runtime_error when the source cannot be created.
   void start();
   /// Stops the thread and destroys the client. Idempotent.
   void stop();
@@ -48,22 +49,33 @@ class Acquisition {
   bool capture_want() const noexcept {
     return capture_want_.load(std::memory_order_acquire);
   }
+
+  /// Asks for one **forced trigger acquisition** -- the trigger panel's Force button. The producer
+  /// consumes the request on its next packet and opens a capture at that packet's newest stamp,
+  /// which the engine's ordinary latch then publishes with the configured pre/post window. The
+  /// request is dropped rather than retried when there is nothing to force: trigger mode off, no
+  /// channel resolved, the engine disarmed, or a capture already filling (a capture in flight *is*
+  /// the acquisition being asked for).
+  ///
+  /// **Write it under `ScopeModel::mutex()`, together with the `armed` flag the click also sets.**
+  /// The producer holds that lock for a whole packet -- it reads the panel's `armed` at the top of
+  /// one and consumes this request at the bottom -- so a request written between the two would be
+  /// read by a packet whose engine was still disarmed, and then dropped.
+  void request_force() noexcept { force_want_.store(true, std::memory_order_release); }
+
+  /// The source this acquisition drives, for the UI's capability panels: it may only call
+  /// `post()` on it. Null until `start()`.
+  DataSource* source() noexcept { return source_.get(); }
+
   /// The capture, for the popover's row and the probe. Counters and errors are read
   /// cross-thread through PacketCapture's own published fields.
   const PacketCapture& capture() const noexcept { return capture_; }
 
  private:
   void run();
-  void on_config(const udps_signal_t* signals, std::uint32_t count, std::uint8_t publish_mode);
-  void on_data(const udps_frame_t* frame);
-  void on_event(int event, const char* detail);
-
-  static void config_trampoline(const udps_signal_t* signals, std::uint32_t count,
-                                std::uint8_t publish_mode, void* user);
-  static void data_trampoline(const udps_frame_t* frame, void* user);
-  static void event_trampoline(udps_event_t event, const char* detail, void* user);
-  static void datagram_trampoline(const std::uint8_t* bytes, std::size_t len,
-                                  double recv_time, void* user);
+  void on_config(const std::vector<SignalInfo>& signals, std::uint8_t publish_mode) override;
+  void on_data(const Frame& frame) override;
+  void on_event(SourceEvent event, const char* detail) override;
   /// Drops the producer state that is per *connection*: the counter mark, the time
   /// anchors and the clock choice. A reconnect re-sends the CONFIG and the stream may
   /// have restarted its numbering; carrying the old session's marks across makes the
@@ -75,9 +87,10 @@ class Acquisition {
   void on_datagram(const std::uint8_t* bytes, std::size_t len, double recv_time);
 
   /// Fills `stamps_` with this frame's base-tick timestamps, in stream seconds,
-  /// and returns how many were written (`frame->num_samples` unless the frame is
+  /// and returns how many were written (`frame.num_samples` unless the frame is
   /// malformed).
-  std::uint32_t build_stamps(const udps_frame_t* frame, int time_signal);
+  std::uint32_t build_stamps(const Frame& frame, int time_signal,
+                             bool counter_gap_refused);
 
   /// Pushes NaN for the `missing` packets' worth of samples that were never delivered,
   /// advances the decimation accumulators and tick_, records the hole in the model, and
@@ -89,17 +102,29 @@ class Acquisition {
   /// Writes a late frame's values into the NaN-filled holes their counter addresses,
   /// amending the value ring directly (producer path) and queuing pyramid amends for
   /// `ChannelBuffer::acquire()` to apply on the consumer thread.
-  void backfill_from(const udps_frame_t* frame, const Partition& part,
+  void backfill_from(const Frame& frame, const Partition& part,
                      const std::vector<ChannelInfo>& channels, BufferStore& store, u64 g);
 
+  /// Keeps the wire's own cadence up to date from the arrival times, in the modes where
+  /// `build_stamps()`'s arrival branch does not (see the definition).
+  void note_frame_arrival(double recv_time) noexcept;
+
+  /// Whether the counter's claim of `missing` lost packets can be believed *and* booked: the
+  /// arrival clock has to corroborate it and the ring has to be able to hold it. See the
+  /// definition for both tests and for what believing a claim that fails them looks like.
+  bool gap_plausible(std::uint32_t missing, double elapsed, const Partition& part, u64 g) const;
+
   ScopeModel& model_;
   Config cfg_;
-  udps_client* client_ = nullptr;
+  std::unique_ptr<DataSource> source_;
   std::thread thread_;
   std::atomic<bool> running_{false};
   std::atomic<bool> paused_{false};
   PacketCapture capture_;
   std::atomic<bool> capture_want_{false};
+  /// The pending Force request (see `request_force()`): a flag and not a queue, because two clicks
+  /// inside one packet are one acquisition, which is what a momentary button means.
+  std::atomic<bool> force_want_{false};
   std::uint32_t capture_slots_ = 1000;
   /// Written once, by the GTK thread, before `capture_want_` is ever published true;
   /// the producer reads it only after the flag, so no lock is needed.
@@ -125,22 +150,42 @@ class Acquisition {
   double arrival_epoch_ = 0.0;
   bool have_arrival_epoch_ = false;
   /// Smoothed interval between two frames' arrivals, and the previous arrival: the
-  /// spine of the arrival-anchored clock (see `build_stamps`).
+  /// spine of the arrival-anchored clock (see `build_stamps`). In relative mode no frame
+  /// reaches that branch, so `on_data` keeps the same pair up to date itself -- the
+  /// reservation's plausibility test below needs a measured cadence whatever clock the
+  /// user chose, and the two writers are mutually exclusive by mode.
   double arrival_interval_ = 0.0;
   double arrival_prev_ = 0.0;
   bool have_arrival_interval_ = false;
+  /// The previous *accepted* frame's receive time, for the one measurement the reservation
+  /// test needs: how much wall time actually passed. Kept apart from `arrival_prev_` on
+  /// purpose -- that one is the arrival clock's own bookkeeping and is re-anchored by the
+  /// clock-choice code, while this is a bare witness of the wire and must never be moved by
+  /// a mode change.
+  double prev_frame_recv_ = 0.0;
+  bool have_prev_frame_recv_ = false;
   /// The stream's time source, chosen once and sticky: 0 undecided, 1 the declared
   /// time signal, 2 arrival. Re-evaluated only on a CONFIG. A per-frame choice
   /// interleaved two timelines in one ring -- some frames stamped from a declared
   /// signal carrying volt-like values, others from the arrival clock -- which is a
   /// time base no reader can make sense of (see `build_stamps`).
   int time_source_ = 0;
-  /// Relative-time mode's position counter: samples seen since the stream began, which is
-  /// what the counter names. Advanced by `batch_` for every packet the counter reports
-  /// missing (before the frame's own samples) and then by the frame's own `n`, so it is
-  /// exactly `counter * batch + sample_index` for a constant batch and degrades gracefully
-  /// when a frame's length disagrees.
-  std::uint64_t slot_base_ = 0;
+  /// Relative-time mode's clock: seconds since the stream began, accumulated at the interval
+  /// the plan declares. Advanced by `lost * batch_` samples' worth for every packet the counter
+  /// reports missing (before the frame's own samples) and then by the frame's own `n`, so it is
+  /// exactly `(counter * batch + sample_index) * dt` for a constant batch and degrades
+  /// gracefully when a frame's length disagrees.
+  ///
+  /// It is a **time**, not a position multiplied by the current plan's interval, and the
+  /// difference is the whole of one defect: a plan is rebuilt whenever the channel list changes
+  /// (a CONFIG, an enable, a session's math channel) and `Partition::base_dt` -- which is the
+  /// 1 kHz fallback until a *streamed* channel declares a rate -- can therefore change under a
+  /// running stream. With `position * dt` a plan that shortened the interval made every later
+  /// stamp *behind* the one already written, which the frame loop's monotonic clamp then held
+  /// for the rest of the run: the timeline stood still, the trigger's `history` never reached
+  /// its pre-window, and nothing was drawn (see `on_data`). Accumulated, a plan change is what
+  /// it is -- a slope change -- and the clock cannot go backwards.
+  double rel_base_s_ = 0.0;
   /// Samples per DATA packet, fixed by the first frame. Only ever needed to size what is
   /// *absent*: a delivered frame carries its own length. 0 until the first frame.
   std::uint32_t batch_ = 0;
@@ -158,11 +203,23 @@ class Acquisition {
   /// Warn-once latch for a loss past the reservation cap. A member, not a function-local
   /// `static`, matching the latch Task 2 added for the same reason.
   bool warned_outage_ = false;
+  /// Warn-once latch for a reservation the arrival clock did not corroborate, or that the ring
+  /// could not hold (see `gap_plausible()`). Once per connection, like the two above.
+  bool warned_phantom_gap_ = false;
   /// Warn-once latch for the one bridged packet whose time signal glitched.
   bool warned_bridge_ = false;
   /// Warn-once latch for the declared time signal failing for good, so the arrival clock is
   /// taken instead.
   bool warned_time_source_ = false;
+  /// Warn-once latch for a frame whose every stamp was held back by the frame loop's monotonic
+  /// clamp. The clamp exists for a stream clock that glitches; a *whole frame* behind the clock is
+  /// the timeline standing still, and while it lasts nothing is drawn and no trigger can latch.
+  bool warned_clock_stall_ = false;
+  /// Whether this connection has adopted its clock origin (`ScopeModel::set_epoch_if_unset()`).
+  /// A state and not `epoch() == 0.0`, which re-fires in relative mode -- where the first frame's
+  /// stamp *is* zero -- and moves the origin under the timeline. Per connection, like every other
+  /// piece of session state here: a new session's clock is a new clock.
+  bool epoch_adopted_ = false;
   /// The re-plan generation this object last reacted to. The buffer is re-planned whenever the
   /// model rebuilds it, and the state tied to the old store (`tick_` and the accumulators) is
   /// reset when this falls behind `ScopeModel::plan_generation()`.

src/channel.cpp

@@ -78,6 +78,18 @@ void ChannelBuffer::invalidate() noexcept {
   pending_amends_.clear();
 }
 
+void ChannelBuffer::republish_from(u64 absolute) noexcept {
+  published_ = absolute;
+  window_x0_ = 0.0;
+  pending_amends_.clear();
+  // `clear()` leaves the pyramid empty at absolute 0, and `drop_before()` past the end
+  // restarts an empty window at the index it is given -- which is the only way to say
+  // "nothing is published, and the next append is sample `absolute`". The no-op guard is
+  // for `absolute == 0`, where `clear()` has already said exactly that.
+  pyramid_.clear();
+  if (absolute > 0) pyramid_.drop_before(absolute);
+}
+
 f64 ChannelBuffer::time_of(u64 absolute_index) const noexcept {
   // Channel sample `j` is produced on the tick that also pushes time slot
   // `j*stride + stride - 1` (see `Acquisition::on_data`): the producer stamps the

src/channel.hpp

@@ -48,6 +48,16 @@ class ChannelBuffer final : public plot::data::Series {
   void acquire() noexcept;
   /// Consumer thread: forgets the published window (after a rebind or a reset).
   void invalidate() noexcept;
+  /// Consumer thread: drops the published window and re-publishes it from absolute sample
+  /// `absolute` on the next `acquire()`.
+  ///
+  /// For a ring whose contents were *rewritten in place* rather than appended to -- a math
+  /// channel recomputed over its inputs' retained window. `acquire()` is incremental, so
+  /// a rewrite that leaves `produced()` where it was publishes nothing and the pyramid goes
+  /// on describing the samples the edit replaced. `invalidate()` would do it too, but it
+  /// restarts at 0 and `acquire()` would then walk every absolute index ever produced; this
+  /// restarts at the oldest index the ring still holds, so the rebuild is one window.
+  void republish_from(u64 absolute) noexcept;
 
   /// Producer thread, under `ScopeModel::mutex()`: records that absolute sample `absolute`
   /// has been backfilled, for `acquire()` to fold into the pyramid.

src/config.cpp

@@ -6,6 +6,7 @@
 // For `RowSet::kMaxRows`: `--plots` names a row count, and one constant for the ceiling
 // is what stops the message and the clamp from drifting apart.
 #include "plot_host.hpp"
+#include "source/registry.hpp"
 
 #include <cstdio>
 #include <cstdlib>
@@ -38,17 +39,61 @@ double parse_double(const char* name, const std::string& v) {
   }
 }
 
+/// A count with an optional decimal suffix: `250000`, `64k`, `100M`, `1.5G`. k, M and G are 10^3, 10^6
+/// and 10^9 -- a *sample* count, not a byte size -- and either case is accepted.
+std::uint64_t parse_count(const char* name, const std::string& v) {
+  std::string digits = v;
+  double scale = 1.0;
+  if (!digits.empty()) {
+    switch (digits.back()) {
+      case 'k': case 'K': scale = 1.0e3; break;
+      case 'm': case 'M': scale = 1.0e6; break;
+      case 'g': case 'G': scale = 1.0e9; break;
+      default: break;
+    }
+    if (scale != 1.0) digits.pop_back();
+  }
+  const double d = parse_double(name, digits) * scale;
+  if (!(d >= 1.0) || d > 1.0e12) fail(std::string(name) + " out of range: " + v);
+  return static_cast<std::uint64_t>(d + 0.5);
+}
+
 }  // namespace
 
+SourceConfig Config::source_config() const {
+  SourceConfig out;
+  if (source_kind == "udps") {
+    out.set("server", server);
+    out.set("port", std::to_string(port));
+    if (!multicast.empty()) out.set("multicast", multicast);
+    if (!interface_addr.empty()) out.set("interface", interface_addr);
+    out.set("recv_buffer", std::to_string(recv_buffer_bytes));
+  }
+  for (const auto& kv : source_opts.items()) out.set(kv.first, kv.second);
+  return out;
+}
+
+std::string Config::session_host() const { return udpscope::session_host(source_kind, source_config()); }
+std::uint16_t Config::session_port() const { return udpscope::session_port(source_kind, source_config()); }
+
 void print_usage(std::FILE* out, const char* argv0) {
+  std::string names;
+  for (const SourceKind* k : kinds()) names += (names.empty() ? "" : ", ") + k->id();
   std::fprintf(out,
-               "usage: %s --server ADDR --port PORT [options]\n"
+               "usage: %s --server ADDR --port PORT [--source NAME] [options]\n"
                "\n"
                "  --server ADDR        stream source IPv4 address (default 127.0.0.1)\n"
                "  --port PORT          UDP port (unicast) or TCP port (multicast) (default 8000)\n"
                "  --multicast GROUP    join GROUP for DATA instead of unicast\n"
                "  --interface ADDR     local IPv4 of the interface to join on\n"
-               "  --buffer-mb MB       size of each of the two sample buffers (default 200)\n"
+               "  --source NAME        source kind (%s; default udps). --server/--port/\n"
+               "                       --multicast/--interface configure udps\n"
+               "  --source-opt K=V     a setting for the source kind; repeatable\n"
+               "  --buffer-samples N   samples kept per acquired signal, e.g. 100M or 250000 (k, M\n"
+               "                       and G are decimal; default 10M). Rounded down to a power\n"
+               "                       of two: 100M gives 67108864\n"
+               "  --memory-limit-mb MB hard ceiling on the sample rings, all signals together\n"
+               "                       (default 8192); the request is halved until it fits\n"
                "  --max-window SEC     largest time window the toolbar offers (default 600)\n"
                "  --holdoff SEC        default trigger hold-off (default 0.010)\n"
                "  --recv-buffer BYTES  SO_RCVBUF for the receiver socket (default 8388608)\n"
@@ -62,8 +107,14 @@ void print_usage(std::FILE* out, const char* argv0) {
                "                       time is then kept for export only\n"
                "  --open FILE          open an exported waveform (.npy) instead of a live source:\n"
                "                       signals from its columns, no socket, no acquisition\n"
+               "  --renderer NAME      render with cairo (software), gl or vulkan. cairo also\n"
+               "                       exports LIBGL_ALWAYS_SOFTWARE=1, because the plot is a\n"
+               "                       GtkGLArea and still needs a GL context. Over SSH/X11\n"
+               "                       forwarding use cairo: Vulkan cannot make a swapchain there\n"
+               "                       and the GL area has no hardware context, so the window\n"
+               "                       never paints or allocates\n"
                "  -h, --help           this text\n",
-               argv0);
+               argv0, names.c_str());
 }
 
 Config parse_args(int argc, char** argv) {
@@ -85,10 +136,28 @@ Config parse_args(int argc, char** argv) {
       c.multicast = value_of(argc, argv, i, "--multicast");
     } else if (a == "--interface" || a.rfind("--interface=", 0) == 0) {
       c.interface_addr = value_of(argc, argv, i, "--interface");
-    } else if (a == "--buffer-mb" || a.rfind("--buffer-mb=", 0) == 0) {
-      c.buffer_mb = parse_double("--buffer-mb", value_of(argc, argv, i, "--buffer-mb"));
-      c.buffer_mb_specified = true;
-      if (c.buffer_mb < 1.0) fail("--buffer-mb must be at least 1");
+    } else if (a == "--source" || a.rfind("--source=", 0) == 0) {
+      const std::string v = value_of(argc, argv, i, "--source");
+      if (find_kind(v) == nullptr) {
+        std::string names;
+        for (const SourceKind* k : kinds()) names += (names.empty() ? "" : ", ") + k->id();
+        fail("unknown source '" + v + "' (available: " + names + ")");
+      }
+      c.source_kind = v;
+      c.source_specified = true;
+    } else if (a == "--source-opt" || a.rfind("--source-opt=", 0) == 0) {
+      const std::string v = value_of(argc, argv, i, "--source-opt");
+      if (!c.source_opts.parse_assignment(v)) fail("--source-opt must be key=value: " + v);
+    } else if (a == "--buffer-samples" || a.rfind("--buffer-samples=", 0) == 0) {
+      c.buffer_samples = parse_count("--buffer-samples", value_of(argc, argv, i, "--buffer-samples"));
+      c.buffer_samples_specified = true;
+      if (c.buffer_samples < 128) fail("--buffer-samples must be at least 128");
+    } else if (a == "--memory-limit-mb" || a.rfind("--memory-limit-mb=", 0) == 0) {
+      const double mb =
+          parse_double("--memory-limit-mb", value_of(argc, argv, i, "--memory-limit-mb"));
+      if (!(mb >= 1.0) || mb > 1.0e9) fail("--memory-limit-mb must be 1..1000000000 (MiB)");
+      c.memory_limit_mb = static_cast<std::uint64_t>(mb);
+      c.memory_limit_specified = true;
     } else if (a == "--max-window" || a.rfind("--max-window=", 0) == 0) {
       c.max_window_s = parse_double("--max-window", value_of(argc, argv, i, "--max-window"));
       if (c.max_window_s <= 0.0) fail("--max-window must be positive");
@@ -113,6 +182,15 @@ Config parse_args(int argc, char** argv) {
       c.capture_packets = static_cast<std::uint32_t>(n);
     } else if (a == "--open" || a.rfind("--open=", 0) == 0) {
       c.open_waveform = value_of(argc, argv, i, "--open");
+    } else if (a == "--renderer" || a.rfind("--renderer=", 0) == 0) {
+      const std::string v = value_of(argc, argv, i, "--renderer");
+      // Only the three a source or a forwarded display actually chooses between. Anything
+      // GTK does not know would fall back with a warning and leave the user reading a
+      // renderer failure that is really a typo, so it is refused here instead.
+      if (v != "cairo" && v != "gl" && v != "vulkan") {
+        fail("--renderer must be cairo, gl or vulkan: " + v);
+      }
+      c.renderer = v;
     } else if (a == "--relative-time") {
       c.relative_time = true;
       c.relative_time_specified = true;

src/config.hpp

@@ -6,10 +6,12 @@
 #include <cstdint>
 #include <string>
 
+#include "source/source_config.hpp"
+
 namespace udpscope {
 
 /// Everything the command line can say. Defaults are the ones the spec names
-/// (200 MB per buffer, 10 ms trigger hold-off) unless the user overrides them.
+/// (10 M samples per signal, 10 ms trigger hold-off) unless the user overrides them.
 struct Config {
   std::string server = "127.0.0.1";   ///< IPv4 dotted quad of the stream source.
   std::uint16_t port = 8000;          ///< UDP port (unicast) or TCP port (multicast).
@@ -21,13 +23,38 @@ struct Config {
   /// `server` valid". The default stays a usable value for every other path.
   bool server_specified = false;
 
-  /// Size of *each* of the two sample buffers, in megabytes. The application
-  /// always allocates two identical buffers (spec item 1).
-  double buffer_mb = 200.0;
-  /// Whether `--buffer-mb` was given. A stored configuration's buffer size fills in only when the
-  /// flag was *absent*: an explicit flag beats a saved setting, and "not asked" is not the same
-  /// question as "asked for 200".
-  bool buffer_mb_specified = false;
+  /// `--source NAME`: which registered kind opens. `udps` is the default, and `--server/--port/
+  /// --multicast/--interface` keep meaning UDPS.
+  std::string source_kind = "udps";
+  /// Whether `--source` was given (the other half of "did the user choose a source").
+  bool source_specified = false;
+  /// Repeatable `--source-opt k=v`: the kind's own settings. For `udps` they overlay the fields above.
+  SourceConfig source_opts;
+
+  /// A source was named on the command line (`--server` or `--source`), so the chooser is skipped.
+  bool has_source() const noexcept { return server_specified || source_specified; }
+  /// The settings the kind's `make()` receives: for UDPS the four connection fields plus the receive
+  /// buffer, then `source_opts` on top.
+  SourceConfig source_config() const;
+  /// The (host, port) that name this source's session file; see `session_host()` in the registry.
+  std::string session_host() const;
+  std::uint16_t session_port() const;
+
+  /// The sample budget: how many samples to keep for **every acquired signal**, and for the shared
+  /// time ring. The rings are powers of two, so the request is rounded *down* to one (`buffer_ticks()`
+  /// in model.hpp) -- "up to" this many -- and the UI shows both figures. 10 M asks for 8 388 608.
+  std::uint64_t buffer_samples = 10'000'000;
+  /// Whether `--buffer-samples` was given. A stored configuration's sample budget fills in only when
+  /// the flag was *absent*: an explicit flag beats a saved setting, and "not asked" is not the same
+  /// question as "asked for 10 M".
+  bool buffer_samples_specified = false;
+
+  /// The hard ceiling on the ring storage, in MiB, for the whole application rather than per source.
+  /// `plan_partition()` halves the rings until they fit under it, so it can clip `buffer_samples`.
+  /// Default 8 GiB; the preferences carry it between runs and `--memory-limit-mb` overrides it.
+  std::uint64_t memory_limit_mb = 8192;
+  /// Whether `--memory-limit-mb` was given, so the stored preference only fills the gap.
+  bool memory_limit_specified = false;
 
   /// Largest time window the toolbar offers, in seconds. The buffer partition is
   /// sized to hold at least this much time (spec: decimation).
@@ -59,6 +86,22 @@ struct Config {
   /// live source. File mode and source mode are exclusive -- there is no acquisition behind a file,
   /// and the chooser's Waveforms page sets this rather than the connection fields.
   std::string open_waveform;
+
+  /// `--renderer NAME`: the GSK renderer to force, by exporting `GSK_RENDERER` **before any GTK
+  /// call**. Empty leaves GTK's own choice alone. `cairo` is the software preset over SSH/X11
+  /// forwarding: it also exports `LIBGL_ALWAYS_SOFTWARE=1`, because the plot's `GtkGLArea` asks
+  /// for a GL context whatever GSK draws with. `gl` is the faster alternative when indirect GL
+  /// works. The variables are read when the renderer/context is created, so setting them anywhere
+  /// after `gtk_init()`/`adw_init()` is a no-op -- which is why this is a `Config` field applied
+  /// at the top of `main()` and not a preference.
+  std::string renderer;
+
+  /// The source chooser's "Guided tour" entry. The tour is drawn on the application's own window,
+  /// which does not exist while the chooser runs, so the request rides on the one value `main()`
+  /// owns and hands to both the chooser and the front end (`open_waveform` and the preferences'
+  /// relative time cross the same way) and the window starts the tour once it is up and laid out.
+  /// It is *not* a preference: it describes this request and nothing else, so nothing persists it.
+  bool tour_pending = false;
 };
 
 /// Parses argv. On `--help` prints usage to stdout and exits(0); on a bad

src/event_series.hpp

@@ -7,6 +7,7 @@
 
 #include <algorithm>
 #include <memory>
+#include <string>
 #include <vector>
 
 namespace udpscope {
@@ -63,8 +64,30 @@ struct EventSnapshot {
   /// already O(n), and the same channel on two rows shares it instead of building and
   /// storing it twice.
   std::vector<plot::data::MinMaxPyramid> pyramids;
+  /// The channel *names* `values` is indexed by, so a snapshot can be re-bound after the channel
+  /// list was rebuilt -- and renumbered -- under it: a persistence layer names its signal and
+  /// resolves that name here, exactly as the trigger engine names its channel and for the same
+  /// reason (an index is a position in a list that any enable, disable or CONFIG renumbers).
+  /// Empty on a snapshot nobody re-binds later (a pause view).
+  std::vector<std::string> channel_names;
 };
 
+/// Bytes one snapshot holds: both stamp arrays, every channel's samples, the pyramids built for
+/// them and the names above. The number the persistence retention is measured in -- a retained
+/// snapshot is a whole window copied out of the ring, so what bounds it is bytes, not a count.
+inline std::size_t snapshot_bytes(const EventSnapshot& s) {
+  std::size_t bytes = s.stamps.size() * sizeof(f64) + s.abs_stamps.size() * sizeof(f64) +
+                      s.y.size() * sizeof(plot::Range) +
+                      s.channel_names.size() * sizeof(std::string);
+  for (const std::vector<f32>& v : s.values) bytes += v.size() * sizeof(f32);
+  // A pyramid entry is 32 bytes (`MinMaxPyramid::Entry`), one per level-`l` bucket of
+  // `kBucket << l` samples -- the whole index is about one byte per sample.
+  for (const plot::data::MinMaxPyramid& p : s.pyramids) {
+    for (u32 l = 0; l < p.level_count(); ++l) bytes += p.level_size(l) * 32u;
+  }
+  return bytes;
+}
+
 /// A plot::data::Series view of one channel of an EventSnapshot. The stamps are
 /// near-uniform (the arrival clock), so dx is the mean spacing and x_at returns
 /// the exact stamp; gather decimates by 2^level like the ring series does.

src/export.cpp

@@ -6,8 +6,11 @@
 #include <algorithm>
 #include <bit>
 #include <cerrno>
+#include <cstdint>
 #include <cstdio>
 #include <cstring>
+#include <ctime>
+#include <utility>
 
 namespace udpscope {
 namespace {
@@ -34,18 +37,29 @@ std::string sanitise(const std::string& name) {
   return out;
 }
 
-/// The final labels: sanitised, and de-duplicated against each other *and* against the
-/// two time columns, with a `_2`, `_3` suffix. Two elements of one vector signal can
-/// easily sanitise to the same string.
-std::vector<std::string> column_labels(const ExportTable& table) {
-  std::vector<std::string> taken{"time", "abs_seconds"};
+/// `base` carrying a `_2`, `_3` … suffix for the `n`-th copy (`n == 1` is the name itself),
+/// cut to `max_len` bytes when one is given -- MDF's name field is 32 bytes wide and the file
+/// is re-read by a reader that keeps only the *first* occurrence of a name, so a cut that made
+/// two channels equal would silently lose one.
+std::string numbered(const std::string& base, int n, std::size_t max_len) {
+  const std::string suffix = n == 1 ? std::string() : "_" + std::to_string(n);
+  std::size_t room = base.size();
+  if (max_len != 0) room = max_len > suffix.size() ? max_len - suffix.size() : 0;
+  return base.substr(0, room) + suffix;
+}
+
+/// The final labels: sanitised, and de-duplicated against each other *and* against
+/// `taken` -- the names the writer already spends -- with a `_2`, `_3` suffix. Two
+/// elements of one vector signal can easily sanitise to the same string.
+std::vector<std::string> column_labels(const ExportTable& table, std::vector<std::string> taken,
+                                      std::size_t max_len = 0) {
   std::vector<std::string> out;
   out.reserve(table.columns.size());
   for (const ExportTable::Column& col : table.columns) {
     const std::string base = sanitise(col.name);
-    std::string label = base;
+    std::string label = numbered(base, 1, max_len);
     for (int n = 2; std::find(taken.begin(), taken.end(), label) != taken.end(); ++n) {
-      label = base + "_" + std::to_string(n);
+      label = numbered(base, n, max_len);
     }
     taken.push_back(label);
     out.push_back(std::move(label));
@@ -69,6 +83,74 @@ bool opened(const File& out, const std::string& path, std::string& error) {
   return false;
 }
 
+/// The block lengths of MDF 3.30, from the **reader's** own field lists
+/// (`asammdf/blocks/v2_v3_constants.py`, 8.8.27): every block is a two-letter id, a 16-bit
+/// length and then its own fields, and the reader walks the file by those lengths alone, so a
+/// block written one field too wide is a file whose reader lands in the middle of the next one.
+/// The widths here are the ones a `bytes(block)` of the reference file measures (the known-good
+/// 3.30 file `/tmp/ref.mdf` this writer was byte-diffed against).
+constexpr std::size_t kMdfIdBlock = 64;         // "MDF     3.30" and the flags, no id/length
+constexpr std::size_t kMdfHeader = 208;         // 164 common + 44 of the 3.2-era time fields
+constexpr std::size_t kMdfTxOverhead = 5;       // "TX", the u16 length and the terminating NUL
+constexpr std::size_t kMdfDataGroup = 28;       // 4 addresses, the group count, 4 reserved
+constexpr std::size_t kMdfConversion = 46;      // a NONE conversion is the common fields alone
+constexpr std::size_t kMdfChannel = 228;        // the display-name-length CNBLOCK
+constexpr std::size_t kMdfChannelGroup = 30;    // 26 + the sample-reduction address of 3.30
+constexpr std::size_t kMdfNameBytes = 31;       // a CNBLOCK's 32-byte name field, less its NUL
+
+/// A byte sink for the MDF header blocks, which are a few hundred bytes each and have to be
+/// laid out field by field. The little-endian `raw()` writes are the same assumption the `.npy`
+/// writer states at the top of this file, and `static_assert`s there.
+struct Bytes {
+  std::vector<unsigned char> v;
+
+  void raw(const void* p, std::size_t n) {
+    const auto* b = static_cast<const unsigned char*>(p);
+    v.insert(v.end(), b, b + n);
+  }
+  void u16(std::uint16_t x) {
+    const unsigned char b[2] = {static_cast<unsigned char>(x & 0xFFu),
+                                static_cast<unsigned char>((x >> 8) & 0xFFu)};
+    raw(b, sizeof(b));
+  }
+  void i16(std::int16_t x) { u16(static_cast<std::uint16_t>(x)); }
+  void u32(std::uint32_t x) {
+    const unsigned char b[4] = {static_cast<unsigned char>(x & 0xFFu),
+                                static_cast<unsigned char>((x >> 8) & 0xFFu),
+                                static_cast<unsigned char>((x >> 16) & 0xFFu),
+                                static_cast<unsigned char>((x >> 24) & 0xFFu)};
+    raw(b, sizeof(b));
+  }
+  void u64(std::uint64_t x) {
+    u32(static_cast<std::uint32_t>(x & 0xFFFFFFFFu));
+    u32(static_cast<std::uint32_t>(x >> 32));
+  }
+  void f64(double x) { raw(&x, sizeof(x)); }
+  void f32(float x) { raw(&x, sizeof(x)); }
+  void zeros(std::size_t n) { v.insert(v.end(), n, 0); }
+
+  /// A fixed-width text field: the bytes, then NUL padding. MDF's names and units are
+  /// NUL-terminated inside a field of a width the reader is told by the block size, so this is
+  /// how every string in the format is spelled.
+  void text(const std::string& s, std::size_t width) {
+    const std::size_t n = std::min(s.size(), width);
+    raw(s.data(), n);
+    zeros(width - n);
+  }
+
+  std::size_t size() const noexcept { return v.size(); }
+};
+
+/// Checked rather than trusted: a field written at the wrong width would not fail here, it
+/// would produce a file whose reader walks into the middle of the next block. The widths are
+/// the asammdf 8.8.27 reader's own field lists (`blocks/v2_v3_constants.py`).
+bool mdf_block_size(const Bytes& block, std::size_t want, const char* what, std::string& error) {
+  if (block.size() == want) return true;
+  error = std::string("internal: the MDF ") + what + " block is " + std::to_string(block.size()) +
+          " bytes, the layout wants " + std::to_string(want);
+  return false;
+}
+
 }  // namespace
 
 ExportTable collect_export(ScopeModel& model, RowSet& rows) {
@@ -97,6 +179,12 @@ ExportTable collect_export(ScopeModel& model, RowSet& rows) {
     return static_cast<std::size_t>(c) < infos.size() ? infos[static_cast<std::size_t>(c)].name
                                                      : std::string("ch") + std::to_string(c);
   };
+  // The unit travels with the column so the MDF writer can put it on the channel; the other
+  // writers ignore it, as they always have.
+  const auto unit_of = [&](int c) {
+    return static_cast<std::size_t>(c) < infos.size() ? infos[static_cast<std::size_t>(c)].unit
+                                                     : std::string();
+  };
 
   // What the rows bind to is what gets exported, so the split is the same `DisplayMode`
   // `RowSet::bind()` switches on: the frozen event only while one is held, the live ring
@@ -136,8 +224,9 @@ ExportTable collect_export(ScopeModel& model, RowSet& rows) {
       if (ch >= snap->values.size()) continue;
       const std::vector<f32>& src = snap->values[ch];
       if (src.size() < first + n) continue;
-      table.columns.push_back({name_of(c), std::vector<f32>(src.begin() + static_cast<std::ptrdiff_t>(first),
-                                                            src.begin() + static_cast<std::ptrdiff_t>(first + n))});
+      table.columns.push_back({name_of(c), unit_of(c),
+                               std::vector<f32>(src.begin() + static_cast<std::ptrdiff_t>(first),
+                                                src.begin() + static_cast<std::ptrdiff_t>(first + n))});
     }
     return table;
   }
@@ -177,7 +266,7 @@ ExportTable collect_export(ScopeModel& model, RowSet& rows) {
     if (ch >= model.channel_count()) continue;
     std::vector<f32> values(static_cast<std::size_t>(n));
     store.values(ch).copy_from(first, n, values.data());
-    table.columns.push_back({name_of(c), std::move(values)});
+    table.columns.push_back({name_of(c), unit_of(c), std::move(values)});
   }
   return table;
 }
@@ -191,6 +280,7 @@ ExportTable event_table(ScopeModel& model, const EventSnapshot& snapshot) {
   for (std::size_t c = 0; c < snapshot.values.size() && c < channels.size(); ++c) {
     ExportTable::Column column;
     column.name = channels[c].name;
+    column.unit = channels[c].unit;
     column.values = snapshot.values[c];
     table.columns.push_back(std::move(column));
   }
@@ -202,7 +292,7 @@ bool write_npy(const std::string& path, const ExportTable& table, std::string& e
     error = "nothing to export: no signal is plotted in the visible range";
     return false;
   }
-  const std::vector<std::string> labels = column_labels(table);
+  const std::vector<std::string> labels = column_labels(table, {"time", "abs_seconds"});
 
   // `descr` as a list of (name, format) pairs is a *packed* structured dtype -- NumPy
   // only inserts alignment padding when asked to (`align=True`) -- so the records below
@@ -266,7 +356,7 @@ bool write_csv(const std::string& path, const ExportTable& table, std::string& e
   File out(path);
   if (!opened(out, path, error)) return false;
 
-  const std::vector<std::string> labels = column_labels(table);
+  const std::vector<std::string> labels = column_labels(table, {"time", "abs_seconds"});
   std::string line = "time,abs_seconds";
   for (const std::string& label : labels) line += "," + label;
   line += "\n";
@@ -302,4 +392,256 @@ bool write_csv(const std::string& path, const ExportTable& table, std::string& e
   return true;
 }
 
+bool write_mdf(const std::string& path, const ExportTable& table, std::string& error) {
+  if (table.empty()) {
+    error = "nothing to export: no signal is plotted in the visible range";
+    return false;
+  }
+  const std::size_t rows = table.rows();
+  const std::size_t cols = table.columns.size();
+
+  // **The master is the absolute clock, named `time`**, and the axis the plot showed goes out as
+  // an ordinary channel, `time_relative`. The relative column is 0 at a different sample in each
+  // display mode, so a master off it would put a live export and a held event's export on two
+  // timelines -- the one thing the second column exists to avoid -- while `abs_seconds` is the
+  // number the stream itself stamped the samples with. Both carry the unit `s`.
+  const std::vector<std::string> labels =
+      column_labels(table, {"time", "time_relative"}, kMdfNameBytes);
+  const std::size_t channels = cols + 2;
+  const std::size_t record = 2 * sizeof(f64) + cols * sizeof(f32);
+  if (rows > 0xFFFFFFFFull) {
+    error = "too many samples for an MDF 3 file: the channel group counts cycles in 32 bits";
+    return false;
+  }
+  if (128 + (cols - 1) * 32 > 0xFFFFu) {
+    error = "too many signals for an MDF 3 record: a channel's start offset is 16 bits";
+    return false;
+  }
+
+  // One channel per column, described once: what the CNBLOCK says about it (where in the record
+  // its samples start, how wide they are, whether it is the master) and what the CCBLOCK says
+  // (its unit). The range is measured from the samples rather than left at zero, so
+  // `range_flag = 1` means what it says.
+  struct Channel {
+    std::string name;
+    std::string unit;
+    std::uint16_t bit_offset;
+    std::uint16_t bit_count;
+    std::uint16_t data_type;  // MDF 3: 2 = float, 3 = double, both in the ID block's byte order
+    std::uint16_t type;       // 0 = value, 1 = master
+    f64 lo, hi;
+  };
+  const auto range_of = [](const auto& values) {
+    if (values.empty()) return std::pair<f64, f64>{0.0, 0.0};
+    const auto mm = std::minmax_element(values.begin(), values.end());
+    return std::pair<f64, f64>{static_cast<f64>(*mm.first), static_cast<f64>(*mm.second)};
+  };
+  std::vector<Channel> chans;
+  chans.reserve(channels);
+  const auto abs_range = range_of(table.abs_seconds);
+  const auto rel_range = range_of(table.time);
+  chans.push_back({"time", "s", 0, 64, 3, 1, abs_range.first, abs_range.second});
+  chans.push_back({"time_relative", "s", 64, 64, 3, 0, rel_range.first, rel_range.second});
+  for (std::size_t i = 0; i < cols; ++i) {
+    const auto range = range_of(table.columns[i].values);
+    chans.push_back({labels[i], table.columns[i].unit,
+                     static_cast<std::uint16_t>(128 + i * 32), 32, 2, 0, range.first, range.second});
+  }
+
+  // Every address in the file, from the fixed block lengths above: the writer therefore knows
+  // where it is going before it writes a byte, which is what lets each block carry its links.
+  const std::string comment = "udpscope export: the visible window, " + std::to_string(rows) +
+                              " samples x " + std::to_string(cols) + " signals";
+  const std::size_t hd_end = kMdfIdBlock + kMdfHeader;
+  const std::size_t comment_addr = hd_end;
+  const std::size_t data_addr = comment_addr + kMdfTxOverhead + comment.size();
+  const std::size_t dg_addr = data_addr + rows * record;
+  const std::size_t ch_addr = dg_addr + kMdfDataGroup;
+  const std::size_t cg_addr = ch_addr + channels * (kMdfConversion + kMdfChannel);
+  const std::uint64_t total = cg_addr + kMdfChannelGroup;
+  if (total > 0xFFFFFFFFull) {
+    error = "the export is larger than an MDF 3 file can address";
+    return false;
+  }
+  const auto cc_addr = [&](std::size_t i) {
+    return ch_addr + i * (kMdfConversion + kMdfChannel);
+  };
+
+  // The wall clock the measurement file was written at. `abs_time` is the same instant in
+  // nanoseconds since the epoch, which is what the 3.2-era header field asks for.
+  const std::time_t now = std::time(nullptr);
+  std::tm tm{};
+  localtime_r(&now, &tm);
+  char date[11] = {};
+  char clock[9] = {};
+  std::strftime(date, sizeof(date), "%d:%m:%Y", &tm);
+  std::strftime(clock, sizeof(clock), "%H:%M:%S", &tm);
+
+  Bytes head;
+  // Identification block: the version string, who wrote the file, and the byte order every
+  // sample in it is in.
+  head.text("MDF     ", 8);
+  head.text("3.30", 8);
+  head.text("udpscope", 8);
+  head.u16(0);    // byte order: Intel, ahead of every value and the float format below
+  head.u16(0);    // float format: IEEE
+  head.u16(330);  // MDF version, digits without the separator
+  head.u16(0);    // code page: latin-1
+  head.zeros(2);  // reserved
+  head.zeros(26); // reserved
+  head.u16(0);    // unfinalised standard flags
+  head.u16(0);    // unfinalised custom flags
+  if (!mdf_block_size(head, kMdfIdBlock, "identification", error)) return false;
+
+  // Header block, which points at the data group and at the comment that follows it.
+  head.raw("HD", 2);
+  head.u16(static_cast<std::uint16_t>(kMdfHeader));
+  head.u32(static_cast<std::uint32_t>(dg_addr));  // first data group
+  head.u32(static_cast<std::uint32_t>(comment_addr));
+  head.u32(0);  // program block: nothing wrote this but us
+  head.u16(1);  // data groups
+  head.text(date, 10);
+  head.text(clock, 8);
+  head.text("", 32);  // author
+  head.text("", 32);  // department
+  head.text("", 32);  // project
+  head.text("", 32);  // subject
+  head.u64(static_cast<std::uint64_t>(now) * 1000000000ull);
+  head.i16(static_cast<std::int16_t>(tm.tm_gmtoff / 3600));
+  head.u16(0);  // time quality
+  head.text("Local PC Reference Time", 32);
+  if (!mdf_block_size(head, hd_end, "header", error)) return false;
+
+  // The comment, in the one text block the file carries: plain words rather than the XML a
+  // writer that also *edits* files keeps its structured properties in.
+  head.raw("TX", 2);
+  head.u16(static_cast<std::uint16_t>(comment.size() + kMdfTxOverhead));
+  head.raw(comment.data(), comment.size());
+  head.zeros(1);
+
+  Bytes tail;
+  // Data group: one channel group, whose channels are chained, and the address of the samples.
+  tail.raw("DG", 2);
+  tail.u16(static_cast<std::uint16_t>(kMdfDataGroup));
+  tail.u32(0);                                         // next data group
+  tail.u32(static_cast<std::uint32_t>(cg_addr));
+  tail.u32(0);                                         // trigger block
+  tail.u32(static_cast<std::uint32_t>(data_addr));
+  tail.u16(1);  // channel groups
+  tail.u16(0);  // record IDs: the group is sorted
+  tail.zeros(4);  // reserved
+  if (!mdf_block_size(tail, kMdfDataGroup, "data group", error)) return false;
+
+  for (std::size_t i = 0; i < channels; ++i) {
+    const Channel& c = chans[i];
+    // Conversion block: the unit lives here and nowhere else in MDF 3, which is where ScryLab
+    // reads a signal's unit from. NONE because the samples are already the physical values --
+    // the table was collected as `f32`, so a conversion would only be a second copy of it.
+    Bytes cc;
+    cc.raw("CC", 2);
+    cc.u16(static_cast<std::uint16_t>(kMdfConversion));
+    cc.u16(1);  // range_flag: the range below is measured, so it is valid
+    cc.f64(c.lo);
+    cc.f64(c.hi);
+    cc.text(c.unit, 20);
+    cc.u16(0xFFFFu);
+    cc.u16(0);  // referenced parameters
+    if (!mdf_block_size(cc, kMdfConversion, "conversion", error)) return false;
+
+    // Channel block: the name ScryLab turns into the signal name, where this channel's samples
+    // sit in a record, and the link to the next channel.
+    Bytes cn;
+    cn.raw("CN", 2);
+    cn.u16(static_cast<std::uint16_t>(kMdfChannel));
+    cn.u32(i + 1 < channels ? static_cast<std::uint32_t>(cc_addr(i + 1) + kMdfConversion) : 0);
+    cn.u32(static_cast<std::uint32_t>(cc_addr(i)));
+    cn.u32(0);  // source: the stream does not say what produced a sample
+    cn.u32(0);  // dependency block
+    cn.u32(0);  // comment
+    cn.u16(c.type);
+    cn.text(c.name, 32);
+    cn.zeros(128);  // description
+    cn.u16(c.bit_offset);
+    cn.u16(c.bit_count);
+    cn.u16(c.data_type);
+    cn.u16(1);  // range_flag
+    cn.f64(c.lo);
+    cn.f64(c.hi);
+    cn.f64(0.0);    // sampling rate: only a virtual time channel carries one
+    cn.u32(0);      // long name
+    cn.u32(0);      // display name
+    cn.u16(0);      // additional byte offset
+    if (!mdf_block_size(cn, kMdfChannel, "channel", error)) return false;
+
+    tail.v.insert(tail.v.end(), cc.v.begin(), cc.v.end());
+    tail.v.insert(tail.v.end(), cn.v.begin(), cn.v.end());
+  }
+
+  // Channel group, last: it names the first channel, the record size and the cycle count from
+  // which a reader derives the size of the sample block at `data_addr`.
+  tail.raw("CG", 2);
+  tail.u16(static_cast<std::uint16_t>(kMdfChannelGroup));
+  tail.u32(0);  // next channel group
+  tail.u32(static_cast<std::uint32_t>(ch_addr + kMdfConversion));
+  tail.u32(0);  // comment
+  tail.u16(1);  // record ID
+  tail.u16(static_cast<std::uint16_t>(channels));
+  tail.u16(static_cast<std::uint16_t>(record));
+  tail.u32(static_cast<std::uint32_t>(rows));
+  tail.zeros(4);  // sample reduction address
+  if (!mdf_block_size(tail, kMdfDataGroup + channels * (kMdfConversion + kMdfChannel) +
+                                 kMdfChannelGroup,
+                      "data group and channels", error)) {
+    return false;
+  }
+
+  File out(path);
+  if (!opened(out, path, error)) return false;
+  const auto put = [&](const Bytes& bytes) {
+    return bytes.v.empty() || std::fwrite(bytes.v.data(), 1, bytes.v.size(), out.f) == bytes.v.size();
+  };
+  if (!put(head)) {
+    error = "short write to '" + path + "': " + std::strerror(errno);
+    return false;
+  }
+  // One record at a time, in the channel order the blocks above declare, so a full ring is not
+  // held twice -- the same shape the `.npy` writer streams its records in.
+  std::vector<unsigned char> rec(record);
+  for (std::size_t i = 0; i < rows; ++i) {
+    std::size_t at = 0;
+    std::memcpy(rec.data() + at, &table.abs_seconds[i], sizeof(f64));
+    at += sizeof(f64);
+    std::memcpy(rec.data() + at, &table.time[i], sizeof(f64));
+    at += sizeof(f64);
+    for (const ExportTable::Column& col : table.columns) {
+      const f32 v = i < col.values.size() ? col.values[i] : 0.0f;
+      std::memcpy(rec.data() + at, &v, sizeof(f32));
+      at += sizeof(f32);
+    }
+    if (std::fwrite(rec.data(), 1, rec.size(), out.f) != rec.size()) {
+      error = "short write to '" + path + "': " + std::strerror(errno);
+      return false;
+    }
+  }
+  if (!put(tail)) {
+    error = "short write to '" + path + "': " + std::strerror(errno);
+    return false;
+  }
+  if (std::fflush(out.f) != 0) {
+    error = "cannot flush '" + path + "': " + std::strerror(errno);
+    return false;
+  }
+  return true;
+}
+
+bool write_export(const std::string& path, const ExportTable& table, std::string& error) {
+  const auto ends_with = [&path](const char* ext) {
+    const std::size_t n = std::strlen(ext);
+    return path.size() >= n && path.compare(path.size() - n, n, ext) == 0;
+  };
+  if (ends_with(".csv")) return write_csv(path, table, error);
+  if (ends_with(".mf3") || ends_with(".mdf")) return write_mdf(path, table, error);
+  return write_npy(path, table, error);
+}
+
 }  // namespace udpscope

src/export.hpp

@@ -21,6 +21,11 @@ namespace udpscope {
 struct ExportTable {
   struct Column {
     std::string name;         ///< the legend name, sanitised for a column label
+    /// The signal's unit exactly as the CONFIG carried it, the empty string when it
+    /// carried none. The `.npy`/`.csv` writers do not spell it out (their readers get the
+    /// names and the numbers); MDF does, because the unit *is* part of what a channel is
+    /// there, and it is the only thing ScryLab reads a signal's unit from.
+    std::string unit;
     std::vector<f32> values;  ///< `rows()` long, the ring's own `f32`
   };
 
@@ -71,4 +76,27 @@ bool write_npy(const std::string& path, const ExportTable& table, std::string& e
 /// enough digits to round-trip each column's own type and no more.
 bool write_csv(const std::string& path, const ExportTable& table, std::string& error);
 
+/// Writes the same table as **MDF 3.30** (`.mf3`/`.mdf`), byte for byte by hand -- there is no
+/// writer library here and MF4 (HDF5) is the one format this app will not link.
+///
+/// One channel group, all channels record-interleaved, master first, which is the shape the
+/// [ScryLab data sources](https://docs.scrylab.de/docs/data-sources/) contract asks for: *every
+/// data channel becomes a signal* (the CNBLOCK's `short_name`), *the master channel of each
+/// group is the x axis* (our master is `abs_seconds`, named `time`), and *the unit is taken from
+/// the channel metadata* (MDF 3 keeps it in the channel's conversion block, the CCBLOCK). A
+/// second occurrence of a name is dropped by that reader, so the labels are de-duplicated and cut
+/// to the 31 bytes a CNBLOCK's name field holds.
+///
+/// The master is the **absolute** clock and the axis the plot showed is an ordinary channel,
+/// `time_relative`: the relative column is `0` at a different sample in every mode, so a master
+/// off it would put two exports from different modes on two timelines, while `abs_seconds` is the
+/// number the stream itself stamped the samples with. Both carry the unit `s`.
+bool write_mdf(const std::string& path, const ExportTable& table, std::string& error);
+
+/// Writes `table` with the writer **`path`'s extension** names: `.csv` -> `write_csv`,
+/// `.mf3`/`.mdf` -> `write_mdf`, anything else -> `write_npy` (the default, as the save dialog's
+/// default filter is). The export dialog and the self-check's export probe both come through
+/// here, so the two cannot offer different formats.
+bool write_export(const std::string& path, const ExportTable& table, std::string& error);
+
 }  // namespace udpscope

src/help/01-overview.txt

@@ -1,78 +0,0 @@
-<b>What udpscope is</b>
-
-udpscope plots a live UDPStreamer source. One window holds up to 8 rows of plots, each with up
-to 4 traces, and every row shares one time axis, so the whole figure scrolls together.
-Acquisition runs on its own thread and writes a ring buffer sized from <tt>--buffer-mb</tt>;
-the drawing thread reads whatever that ring holds when a frame starts, which is why a trace
-never makes the window stutter.
-
-The stream is the clock. Every interval you read on screen is measured between timestamps the
-source sent, never your machine's, so a stalled source freezes the view instead of scrolling it
--- and a source whose clock steps still gets the window you asked for.
-
-The time axis is <i>relative to now</i>. While streaming it is a fixed <tt>[-window .. 0]</tt>
-with the newest sample at 0, so x reads as an age: <tt>-1.5s</tt> is a sample a second and a half
-old. In trigger mode 0 is the event's edge instead, and a paused view keeps the ages it was
-frozen with. The source's own clock is still there when you need it -- an export writes it as a
-second column.
-
-<b>How to reach it</b>
-
-Start the app with a source (<tt>udpscope --server 127.0.0.1 --port 8000</tt>), or start it with
-no <tt>--server</tt> and pick one from the chooser, which lists the sessions you have opened
-before. A unicast source serves one client at a time: if a second viewer connects, they take
-turns and the status bar says so. To watch one source from several instances, use
-<tt>--multicast</tt> with the group and <tt>--interface</tt> with the local address.
-
-The signals arrive <i>disabled</i>. Nothing is acquired until you turn one on in the signal
-list, and enabling is what starts acquisition -- so a freshly opened scope with an idle side
-panel is working correctly, not failing to connect.
-
-<b>The window</b>
-
-• <b>The header bar</b> -- left to right: the time window (<tt>2 s</tt>), the trigger and the
-  pause, then the pane switches -- signal list, cursors, measurements, math, side panel -- and
-  the menu, which holds Fit to data, the layout editor, Export, Keyboard shortcuts, Help and
-  About.
-
-• <b>The side panel</b> -- the trigger, cursors, measurements and math panes at the top, then
-  the signal list: one row per signal with its colour, an enable switch, its name and its unit.
-  Signals are dragged from here onto a plot row.
-
-• <b>The plot</b> -- up to 8 rows, each with its own y axis and up to 4 traces, all on one
-  shared time axis. Right-click a row for its own menu (fit, add a signal, remove a trace).
-
-• <b>The status bar</b>, directly above the plot's bottom edge -- the state word, the stored
-  sample rate and the window, and the ⓘ beside it for packets, gaps and the buffer's own
-  figures. The second screenshot above is what a held capture looks like: <tt>event held</tt>,
-  the axis pinned to the event, and the trigger marker at the edge.
-
-<b>The first five minutes</b>
-
-1. <b>Connect.</b> With no <tt>--server</tt>, pick a stored session or type a host and port.
-2. <b>Enable a signal</b> in the signal list. The plot stays empty for the first fraction of a
-   second while the first window fills -- the buffer holds only what has arrived.
-3. <b>Drag it onto a row.</b> Drop a second signal on another row, or the same signal again for
-   a second view of it. The colour is per signal, so it is the same one wherever it appears.
-4. <b>Set the window</b> with the control in the header bar: type a number, pick a unit, or step
-   a decade. The trigger's event window is a share of this span, so a window change moves it.
-5. <b>Pause</b> (<tt>space</tt>) to look at a still picture; the producer keeps filling the
-   buffer behind it, and resuming shows what arrived meanwhile rather than a hole.
-6. <b>Arm the trigger</b> (<tt>a</tt>) and wait for a latch: the view freezes on one event, and
-   you can zoom in on it. Disarming mid-capture keeps what the capture got.
-7. <b>Measure it</b> -- the measurements pane computes a statistic of the visible window, and
-   <b>show on plot</b> marks it as a ruler or a pair of markers.
-8. <b>Save the data</b> with Export visible range, which writes the plotted signals over the
-   window at the stored rate to <tt>.npy</tt> or <tt>.csv</tt>.
-
-<b>Worth knowing</b>
-
-• A signal nobody enables costs nothing -- no buffer, no socket work, no measurements.
-• The window remembers itself. Rows, traces, the time window, calibration, which signals were
-  enabled, the math channels with their graphs, and the measurements are written per host and
-  port, and reloaded the next time you open that source.
-• A very wide window on a fast stream is drawn from averaged groups of samples, so the rate in
-  the status bar falls: that is the anti-alias filter, not a fault -- striding would fold a fast
-  signal back as a slow one, which looks entirely plausible on screen.
-• Every instrument the app computed -- the trigger marker, the measurement marks -- is locked to
-  the pointer's reach. The cursors are yours to drag; those are not.

src/help/02-source.txt

@@ -1,42 +0,0 @@
-<b>Choosing a source</b>
-
-A source is a host and a port, optionally reached through a multicast group on a named
-interface. Pass it on the command line, or let udpscope ask.
-
-<b>How to reach it</b>
-
-Run with <tt>--server</tt> and the app connects straight away. Run <i>without</i>
-<tt>--server</tt> and a chooser appears first: one row per stored <i>configuration</i>
-(<tt>host:port · name</tt>, its note, and the settings it carries), newest first, plus a
-<b>New host…</b> form that takes the address <i>and</i> the configuration it belongs to — its name
-and note, the <b>buffer size</b>, and whether time is relative or absolute. A row's pencil button
-opens the same form on that configuration, pre-filled, and changes to its name or address move it
-(the old file is deleted).
-
-The second page, <b>Waveforms</b>, opens an <i>exported</i> run instead of a live source: the files
-opened before (newest first; one that has since been deleted is marked <i>missing</i>) and an
-<b>Open…</b> button for a new one. The same file can be opened straight from the command line with
-<tt>--open FILE</tt>. A waveform is a source that never arrives — no socket, no acquisition, no
-starvation notice — and every instrument works on it: cursors, measurements, math channels and
-another export. Only <tt>.npy</tt> files are read. form for one it has not seen. The chooser runs before any
-buffer is allocated and before any socket is opened, so declining it costs nothing.
-
-<b>Worth knowing</b>
-
-• The list is the sessions that <i>named a signal</i>. A session whose streamer was down
-  stores empty slot names and is filtered out, which is what keeps the list the sources you
-  actually configured rather than every port you have ever typed.
-• A stored row reconnects the way it was reached. The multicast group and the interface are
-  written inside the session file, because the file's name (<tt>host_port.toml</tt>) cannot
-  carry them.
-• <tt>--multicast</tt> still needs <tt>--server</tt>: the CONFIG message is fetched from the
-  server, not from the group.
-• The <tt>×</tt> beside a row deletes that session file. Nothing else is removed.
-
-<b>Example</b>
-
-<tt>udpscope</tt> with two stored sessions lists
-<tt>127.0.0.1:8000  plots=1 signals=3</tt> and
-<tt>10.0.0.5:8001  plots=2 signals=4 multicast=239.1.2.3 interface=10.0.0.9</tt>.
-Activating the first reports <tt>[sources] picked 127.0.0.1:8000</tt> and continues into
-the scope with that session's layout already loaded.

src/help/03-signals.txt

@@ -1,36 +0,0 @@
-<b>Signals and calibration</b>
-
-The source's CONFIG message describes its signals: a name, a unit and a type. udpscope turns
-each enabled signal into a <i>channel</i> — a ring of values beside the shared time ring —
-and a channel is what a trace plots. Calibration is a scale and an offset applied at ingest.
-
-<b>How to reach it</b>
-
-The side panel (<tt>s</tt>) lists every signal with a switch. The <b>Signal list</b> item in
-the overflow menu opens the editor where the unit and the calibration live.
-
-<b>Worth knowing</b>
-
-• Signals start disabled, and enabling one is what starts acquiring it. A trigger on a signal
-  nobody acquires can never fire, so arming a trigger enables its signal for you.
-• <b>Calibrate</b> in a signal's row menu opens the gain and offset it is <i>currently</i> drawn
-  through, so a trace already scaled by a gain of 2 shows 2 — pressing <i>Apply</i> confirms it
-  rather than resetting it. A signal nobody calibrated shows the identity, 1 and 0.
-• Calibration is applied <i>at ingest</i>, so changing it re-plans the buffer and drops the
-  history. So does enabling or disabling a signal, and so does a new CONFIG. An empty plot
-  for a second after one of those is the ring refilling, not a fault.
-• The stream's first signal is usually its <i>timestamp</i>, and that one is never acquired.
-  It cannot be plotted, measured or used as a math source, and udpscope refuses to put it in
-  a row rather than binding a trace that would read nothing for ever.
-• A signal's colour follows the <i>signal</i>, not the slot, so the same signal on two rows
-  is one colour and the side panel's chip identifies it unambiguously. A signal on no row
-  gets a grey chip rather than none, so the panel's rows keep their height.
-• <b>Click a coloured chip to change that signal's colour.</b> A grey chip names no trace, so
-  it is not clickable. The colour is saved with the session; <b>Default colour</b> in the
-  signal's ⋯ menu gives the palette entry back.
-
-<b>Example</b>
-
-A source declaring <tt>time</tt>, <tt>sine</tt>, <tt>ramp</tt> and <tt>noise</tt> yields three
-plottable signals. Enable all three and the exit dump reads <tt>3 signals, 3 channels</tt>;
-<tt>time</tt> is not among them.

src/help/04-layout.txt

@@ -1,39 +0,0 @@
-<b>Rows, layout and drag &amp; drop</b>
-
-The figure is a stack of rows, 1 to 8 of them, each holding up to 4 traces. Rows share one
-time axis and one pair of side margins, so their y labels line up, their data areas start and
-end on the same two columns, and their windows cannot drift apart. The left margin holds the y
-labels; the right one is empty, and is there so the newest tick's label and the newest sample's
-ink have somewhere to land instead of sitting on the frame.
-
-<b>How to reach it</b>
-
-Drag a signal's chip out of the side panel (<tt>s</tt>) and drop it on a row to add a trace.
-Press <tt>l</tt>, or pick <b>Layout editor</b> from the overflow menu, to add and remove rows:
-a <tt>×</tt> appears at the top left of each row and a <tt>+</tt> on each boundary between
-rows, including above the first and below the last. The editor's own button in the top-right
-corner leaves it.
-
-<b>Worth knowing</b>
-
-• A plot's own <b>right-click menu</b> (the same compact rows as the app's menu) holds the
-  y-axis scale, the two fits, and <b>Remove signal</b>, which swaps the menu to that plot's traces
-  plus <i>All traces on this plot</i> — with a <b>Back</b> row to return. That is how a trace comes
-  off a row without going through the layout editor.
-• A drop <i>adds</i> a trace to the row's next free slot; it does not replace one. With four
-  traces already on a row the drop is refused.
-• Inserting a row moves the rows below it <i>with their contents</i>. Inserting above row 1
-  puts what row 1 plotted onto row 2 and leaves the new row empty — the rows are not
-  renumbered under you.
-• A trace is remembered by the signal's <i>name</i>, not by its channel number, because a new
-  CONFIG or an enable renumbers the channels and an index would silently re-point the trace.
-• Adding or removing a row rebuilds the figure, which is cheap, but it also re-deals every
-  trace. A frozen trigger event survives the rebuild: the pinned window is restated rather
-  than re-framed on the live edge.
-
-<b>Example</b>
-
-With three traces on row 1, pressing <tt>l</tt> shows 3 buttons (one <tt>×</tt>, two
-<tt>+</tt>). Clicking the <tt>+</tt> above row 1 gives 2 rows and 5 buttons, with the three
-traces now on row 2 — the layout probe reports exactly this as
-<tt>rows=2 buttons=5 traces=[0:-|1:sine,ramp,noise]</tt>.

src/help/05-window.txt

@@ -1,33 +0,0 @@
-<b>Time window</b>
-
-The window is how much time the plot shows. Every row shares one window: the figure has a
-single x link group, so the rows cannot drift apart. The trigger's event span follows it, and
-the pre-trigger share is a share of <i>this</i> window.
-
-<b>How to reach it</b>
-
-The header bar's window button opens a popover: type a number, pick a unit under it, or step a
-decade with the arrows. The button's own label is a reading of the current window in a natural
-unit, width-locked so a change of window cannot widen the header bar.
-
-<b>Worth knowing</b>
-
-• A window too long to store at the wire rate is <i>decimated, not refused</i>. The shared clock
-  takes a power-of-two stride, and each group of samples is <b>averaged</b> rather than strided,
-  so a tone above the stored Nyquist is attenuated instead of aliasing to a false low frequency.
-• The stamp stored for a group is the group's <i>mean</i>, which is where the averaging puts the
-  value. Stamping at the end of a group would shift every trace half a stored sample late.
-• Moving the window across a decimation boundary rebuilds the buffer and drops the history.
-  Walking it inside one decade is free.
-• <b>This control is the only thing that changes the window.</b> A zoom, a pan or a fit moves the
-  view <i>inside</i> it and leaves it alone — which is the point of the previous bullet: a wheel
-  notch that redefined the window could re-plan the buffer and throw your samples away.
-• The trigger sees the <i>stored</i> (filtered) signal, not the wire signal, because an edge
-  found on a sample that is not in the buffer could not be cut out of it.
-
-<b>Example</b>
-
-1 MS/s with 200 MB of buffer. A 2 s window stores every sample (<tt>time x1</tt>). Widen it to
-600 s and the stride becomes <tt>x16</tt>: 625 S/s stored, anti-aliased at 312.5 Hz. A 2 kHz
-sine seen through that window reads <tt>y=[-0.059, 0.079]</tt> — attenuated to about 6%, not
-folded down to a full-amplitude 125 Hz one.

src/help/06-navigate.txt

@@ -1,59 +0,0 @@
-<b>Navigating the plot</b>
-
-The plot pans and zooms with the mouse and with the keyboard. Every gesture acts on the row the
-pointer is over, and because the rows share one time axis, an x change moves all of them.
-
-<b>How to reach it</b>
-
-<b>Wheel</b> zooms both axes · <b>Shift+wheel</b> zooms x only · <b>Ctrl+wheel</b> zooms y only.
-<b>Drag</b> pans · <b>Shift+drag</b> is a box zoom on both axes · <b>Ctrl+drag</b> on x only ·
-<b>Alt+drag</b> on values only.
-The area being chosen is framed while you drag it, so you can see what the release will apply.
-<b>+</b> and <b>-</b> zoom both axes; <b>Ctrl</b> with them restricts to x, <b>Alt</b> to y.
-<b>Arrow keys</b> pan, <b>f</b> fits, <b>Escape</b> cancels a gesture in progress.
-The full table is in the shortcut overview (<tt>Ctrl+/</tt>).
-
-<b>Worth knowing</b>
-
-• The keyboard zoom's modifiers are <i>not</i> the wheel's, and that is deliberate: on common
-  layouts <tt>+</tt> <i>is</i> shift+<tt>=</tt>, so a bare zoom-in already arrives with Shift
-  set and Shift could not mean anything. Ctrl/Alt mirror the box-zoom drags instead.
-• A <i>pinned</i> view is navigable within its own data but cannot leave it. While an event is
-  held, a capture is filling, or the view is paused, a zoom <i>in</i> works normally — "not
-  outside the event" is not "not readable" — but a pan or a zoom out is clamped to the data.
-• Nothing you do on the plot changes the <i>time window</i> — only the header control does. A
-  zoom or a pan moves the view inside the window; <b>f</b> (and Fit X axis) is the <i>undo</i> of a
-  zoom, so a 2 s window zoomed into reads 2 s again. The window is more than the axis: it is also
-  the trigger's event span and how the samples are stored, so a wheel notch that redefined it
-  would re-plan the buffer and drop your history.
-• The axis does not scroll — the <i>data</i> does. A live axis is a fixed <tt>[-window .. 0]</tt>
-  with the newest sample at 0, so the labels stand still and the trace rolls under them. The
-  cursors stand still with the labels (they are positions on screen, so a cursor you placed stays
-  where you put it, over newer data each frame), while a measurement's marks travel with the
-  sample they measured and leave the view when it does.
-• A live view is clamped to the window you asked for, not to what the ring happens to hold.
-  That is why a buffer that has only just started filling leaves its left-hand side empty
-  instead of squeezing the window down to the first few samples.
-• Zooming hard into a held capture is exact. The renderer finds the visible samples by binary
-  search over the real timestamps, never over a nominal sample grid, so a capture whose clock
-  wandered does not drift away from its axis as you zoom.
-• A trace holding far more samples than the plot has pixels is drawn <i>one pixel column at a
-  time</i>: each column is a single vertical line from the lowest to the highest value that falls
-  in it. Drawn as a polyline instead, such a window puts three or four near-vertical lines in
-  every column at slightly different sub-pixel positions, and how they overlap beats against the
-  pixel grid — which reads as bands of light and dark that <i>crawl</i> as you pan. One line per
-  column removes the beat, and it is also much faster: a 1 MS/s view costs a couple of thousand
-  line segments a frame instead of a couple of hundred thousand.
-• Those columns are <i>graded by brightness</i>, the way a digital-phosphor scope reads: bright
-  where the signal spent its time, faint where it only passed through. A column's highest and
-  lowest value are the same whether the samples in it are spread evenly or piled at its two ends,
-  so the grading is what tells the two apart — the flat parts of a square wave come out solid and
-  the edges between them faint. It is read from a finer division of each column rather than from
-  the line that is drawn, and it costs about a millisecond a frame.
-
-<b>Example</b>
-
-Pause a live view, then press <tt>Ctrl++</tt>: x narrows and y does not move. Press
-<tt>Alt++</tt>: y narrows and x does not. Eight doublings into a held 2 s capture, the trace
-still reaches both margins — the zoom probe reports <tt>gap_px</tt> and <tt>end_px</tt> within
-a pixel or two at every step.

src/help/07-pause.txt

@@ -1,31 +0,0 @@
-<b>Pause and play</b>
-
-Pause freezes the <i>display</i>, not the acquisition. The producer keeps filling the ring at
-full rate; the view binds an immutable snapshot of the window that was on screen, and the axis
-is pinned to it.
-
-<b>How to reach it</b>
-
-The pause button in the toolbar, or <tt>Space</tt>. Press it again to resume, which rebinds the
-live ring and puts the window back on the newest data.
-
-<b>Worth knowing</b>
-
-• Nothing is lost while paused. Because the producer never stops, resuming shows current data
-  with no hole in the history behind it.
-• The axis is pinned to the <i>snapshot's own stamps</i>, not to the window that was requested.
-  A window reaching back past the oldest retained sample yields a shorter snapshot, and the
-  pinned axis is that shorter span — so you see a narrower view rather than an empty margin.
-• A paused view is pinned exactly as a held trigger event is: zoom in freely, but a pan or a
-  zoom out is clamped to the snapshot's data.
-• Pausing is the easiest way to measure a layout or read a cursor precisely, because nothing
-  under the pointer moves between frames.
-• The status bar says how long you have been paused — wall time, since the stream itself never
-  stopped. It is there so a frozen picture cannot be mistaken for a live one that went quiet.
-
-<b>Example</b>
-
-Pause with a 2 s window over a ring holding 1.4 s: the frozen axis reads
-<tt>[-1.40 .. 0.00]</tt> rather than <tt>[-2.00 .. 0.00]</tt> with 0.6 s of blank. The pause
-probe reports <tt>ring_produced</tt> still growing across the pause and
-<tt>event_size</tt> non-zero exactly while paused.

src/help/08-trigger.txt

@@ -1,76 +0,0 @@
-<b>Trigger</b>
-
-The trigger watches one signal for a condition and captures a window around it. The
-<b>Shape</b> dropdown chooses what counts as an event; the arming, hold-off, pre/post window
-and Normal/Single mode are the same for all four shapes.
-The captured window is frozen on screen until you re-arm.
-
-<b>How to reach it</b>
-
-The trigger button in the toolbar (<tt>t</tt>) reveals the trigger panel: the signal, the level,
-the shape, the edge (rising, falling, either), the mode (Normal or Single) and the pre-trigger
-share. <b>Arm</b> starts watching; <tt>a</tt> arms and disarms from the keyboard.
-<b>Search the buffer</b> is at the foot of the same panel.
-
-<b>Worth knowing</b>
-
-• <b>Every triggered acquisition is kept.</b> Latches are written to the event cache
-  (<tt>~/.cache/udpscope/events/&lt;source&gt;/</tt>) as a <tt>.npy</tt> of the event, a
-  <tt>.txt</tt> of what it was, and a <tt>.bmp</tt> picture drawn from the samples. The
-  <b>Events</b> pane on the left -- opened from the toolbar's event-history button, which appears
-  while recording is enabled, and collapsed until you ask for it -- lists the last 32 newest first
-  (time, duration, signals, rate), each row with its own picture beside the numbers. Clicking a row
-  <i>replays</i> it: the stored event is loaded exactly like an exported file, <b>without changing the
-  layout</b> -- the rows, the colours, the window, the cursors and the measurements stay where they
-  are and read the stored data instead. A replay leaves trigger mode, because a file has no edge to
-  wait for, and the pane stays open. Drag the pane's edge to resize it. <b>Live</b> goes back to the
-  stream; the status bar names the file until you do.
-  Select two or more events in the list and the two buttons under the header act on them:
-  <b>Compare</b> puts two events in two plots side by side, keeping the layout you have -- one plot per
-  event, the axes synchronised, so zooming a row in one zooms the same row in the other -- and
-  <b>Accumulate</b> overlays up to four of them in the same traces, translucent, so where they agree
-  the trace is brighter. Your own traces stay where they are in both. They need events with the same
-  signals and the same length. A single click selects, a <i>double</i> click replays.
-  <b>Record events</b>, in the trigger panel with the trigger's other options, is what decides whether
-  anything is kept. It is <b>off by default</b> -- nothing is written to disk until you ask -- and
-  with it off the history button goes with it.
-
-• Arming <i>enables</i> the signal if it was off, because a trigger on a signal nobody acquires
-  can never fire.
-• The pre-trigger share is a share of the <i>display window</i>, not of the ring. A 2 s window
-  at 50% captures 1 s before the edge and 1 s after.
-• There are four display states, and the status bar names each: <tt>armed</tt> (watching,
-  nothing drawn yet), <tt>capturing</tt> (the edge was accepted and the post window is filling
-  <i>in view</i>, with the marker at x = 0), <tt>event held</tt> (the frozen capture) and
-  <tt>disarmed</tt>. A held capture is never quietly replaced by live data.
-• The first edge after arming is only accepted once the history reaches back a full pre-trigger
-  window, so a capture may legitimately be shorter than you asked for. The axis is pinned to
-  what the capture actually got.
-• Disarming <i>during</i> a capture publishes what the capture got to, so the picture on screen
-  at that moment stays on screen. No event fired, so the event count does not move.
-• The trigger reads the <b>stored</b> signal — decimated and averaged — not the wire signal.
-  A spike narrower than one decimation group is filtered away rather than triggering on data
-  the buffer does not contain.
-• The four shapes: <b>edge</b> — a crossing of the level in the chosen direction, the classic
-  behaviour. <b>Pulse width</b> — a crossing and its return, qualified by how long the excursion
-  lasted: less than, greater than, within or outside a pair of widths; the event is timed at the
-  closing edge. <b>Window</b> — the signal entering or leaving a band between two levels; the
-  panel keeps the two levels at least one increment apart, because a zero-width band is not a
-  band: the condition becomes an exact float-equality test against the level, which an ordinary
-  signal never satisfies and a signal sitting at the level satisfies on every transition.
-  <b>Dropout</b> —
-  the absence of a crossing for longer than a timeout; one event per outage, re-arms when a
-  crossing returns.
-• The shape's own rows are the only ones shown; the rest are hidden, so the panel never offers
-  a pulse width to a window trigger.
-• <b>Search the buffer</b> runs the same condition over the whole retained ring and lists every
-  place it holds. The arrows step through hits; each step pauses on the hit, centred, exactly as
-  the Pause button does. Up to 16 hits in the visible window are marked on every row; when there
-  are more the panel says how many and suggests zooming in. The search uses the trigger's own
-  condition, set in one place, so a hit is by construction an instant the trigger would have fired.
-
-<b>Example</b>
-
-A 1 Hz sine, level 0, rising, 2 s window at 50%, Single. The capture spans
-<tt>[-1.000 .. 1.000]</tt> with <tt>n=20001</tt> samples at 10 kS/s — the span times the real
-rate, plus one — and the marker sits at x = 0 throughout.

src/help/09-cursors.txt

@@ -1,50 +0,0 @@
-<b>Cursors</b>
-
-Cursors read values off the traces. There are two kinds: one <i>shared vertical pair</i> that
-every row carries at the same time, and <i>horizontal rulers</i>, one pair per row, that belong
-to that row alone.
-
-<b>How to reach it</b>
-
-The cursors button in the toolbar, or <tt>c</tt>. The pane below the plot shows the readings and
-owns a <b>Reset</b> button. Drag a marker to move it. The mode dropdown offers four modes:
-<tt>vertical</tt> (the shared time pair), <tt>horizontal</tt> (the per-row rulers),
-<tt>both</tt>, and <tt>mix</tt>.
-
-<b>Worth knowing</b>
-
-• The vertical pair is <i>one</i> time for the whole figure, so moving it on any row moves it on
-  all of them. That is what makes <tt>dt</tt> meaningful across rows.
-• A ruler belongs to its row and nothing shares it, so two rows' rulers are independent.
-• <tt>mix</tt> is the reading mode: one line per <i>bound</i> trace, with the trace's own values
-  at each marker and their difference. A slot with a name but no channel behind it is not a
-  trace and gets no line.
-• A value is the <i>nearest stored sample's</i>, never a number between two samples. Zoom in past
-  the sample spacing and the line between two samples is something the plot drew, not data —
-  so a reading off it would be the drawing. The hover crosshair reads the same way.
-• Every reading carries a <i>metric prefix</i> so the digits sit in <tt>1..999</tt>:
-  <tt>10.52 mV</tt>, not <tt>0.01 V</tt>. Two decimals is all an instrument landing on an
-  <tt>f32</tt> sample can claim, so without the prefix a small value would read <tt>0.00</tt>
-  and the reading would be gone. A stream that declares no unit gets the prefix anyway, written
-  tight against the number (<tt>585.24m</tt>) — the space separates the number from its unit,
-  and a spaced <tt>m</tt> with nothing after it would read as metres.
-• A marker past the newest sample reads <tt>--</tt>. With only one marker over data the row
-  reads <tt>partial</tt>: a difference between a number and nothing is not a number.
-• In <tt>mix</tt> each marker also places a crossing annotation per trace, which is what lets
-  you see on the plot which sample a number came from. It is <i>on that sample</i>, so when the
-  marker falls between two it sits a little off its own line: the line is where you put the
-  marker, the dot is the datum being quoted. The hover crosshair's mark snaps the same way, and
-  is drawn larger than a trace's sample dots so it does not read as one more sample.
-• The time row exists only in the modes that show the vertical pair. <tt>horizontal</tt> has no
-  time row, by design.
-• A cursor <i>stays where you put it</i> while a live view rolls under it, which is what a bench
-  scope does: its <tt>T0</tt> is an age, so a marker left at <tt>-1.5s</tt> keeps reading the
-  sample a second and a half old as the stream advances. A measurement's marks do the opposite —
-  they travel with the sample they measured — because a cursor is a question you asked and a mark
-  is an answer about one particular sample.
-
-<b>Example</b>
-
-Three traces in <tt>mix</tt> mode with both markers over data: 3 lines and 6 crossing marks,
-each line reading like <tt>sine  0.31 V  -0.84 V  -1.15 V</tt>. Move the second marker past the
-newest sample and the third column reads <tt>--</tt>.

src/help/10-measurements.txt

@@ -1,60 +0,0 @@
-<b>Measurements</b>
-
-A measurement is a statistic of the <i>visible window</i> of one signal, recomputed as that
-window moves. The pane lists them with their values; each can also draw its result on the plot.
-
-<b>How to reach it</b>
-
-The measurements button in the toolbar, or <tt>m</tt>. The pane's <tt>+</tt> adds one; clicking
-a row opens the dialog where the signal, the type, the threshold share and the on-plot marks are
-set, with <b>Save</b> and <b>Delete</b>.
-
-<b>Worth knowing</b>
-
-• The types are average, top, bottom, min, max, peak to peak, amplitude, pulse duration, period
-  and frequency. <i>top</i> and <i>bottom</i> are the means of the upper and lower halves, which
-  is why a unit sine reads 0.637 (2/π) rather than 1.
-• The on-plot marks come in two kinds and the mix is the reading: a <i>level</i> mark is a ruler
-  at a value, a <i>time</i> mark is a marker at a position. An average draws one level mark; a
-  max draws a level mark <i>and</i> a time mark at the first sample that reached it.
-• Marks cannot be dragged. A measurement mark says what the measurement measured, so it is
-  created unselectable — as is the trigger marker.
-• A pass is throttled to a cadence rather than run every frame, so a ruler over a live view is
-  <i>stepped</i>. The number and the ruler come from the same pass, so they always agree.
-• An invalid pass keeps its <i>level</i> marks and drops its <i>time</i> marks. A level is a
-  property of the signal and outlives the window; a position inside the window does not. That is
-  what stops the rulers blinking off at a mode change.
-• A crossing is counted with <i>hysteresis</i>, not on a bare level: the thresholds are a tenth of
-  the window's peak to peak either side of the share, and an edge is counted only once the signal
-  has passed the far one. Period, frequency and pulse duration all depend on it. The mid level is
-  exactly where a waveform moves fastest, so any interferer faster than the fundamental recrosses a
-  single level several times per real crossing — a 5 Hz sine with a 500 Hz tone at a tenth of the
-  amplitude reads 39 Hz without the band and 5 Hz with it. The band holds to an interferer a third
-  of the waveform's own size.
-• The band is clamped to stay inside the data, which is what keeps a threshold set near an extreme
-  usable: a fixed band there would sit above every sample and the measurement would read nothing.
-  A share near an extreme still leaves the band little room, so it rejects less — which is one
-  reason period and frequency offer no share to set.
-• A window with too few crossings reads <tt>invalid</tt> / <tt>--</tt> rather than a plausible
-  invented number. Frequency over a window holding one edge is the usual case.
-• <tt>frequency</tt> is reported in Hz and <tt>period</tt>/<tt>pulse duration</tt> in seconds;
-  every other type carries the channel's own unit. A value is written with a <i>metric prefix</i>
-  so its digits sit in <tt>1..999</tt> — <tt>636.62 mV</tt>, not <tt>0.64 V</tt> — including when
-  the stream declares no unit at all, which is always the case for a math channel: there the
-  prefix goes tight against the number (<tt>636.62m</tt>), since two decimals of an unprefixed
-  small value is <tt>0.00</tt>.
-• Cost is bounded by reading the summary pyramid the producer already maintains, not the raw
-  window. The values are still exact: a bucket's sum is a sum.
-• <b>Statistics</b> adds a second line to every measurement showing <tt>n</tt>, the mean, the
-  standard deviation and the range. Each observation is one <i>recompute</i> of the pane, so
-  <tt>n</tt> counts windows measured, not samples — a mean frequency over many windows is what
-  that claims to be. <b>Reset</b> clears every accumulator and starts fresh. A change of display
-  window, a CONFIG or a measurement edit also resets; a pause, a resume, a zoom, a pan and the
-  toggle itself do not, so turning the line off to read the plot and back on again keeps the history.
-
-<b>Example</b>
-
-On a 1 Hz ±1 sine: <tt>average=0</tt>, <tt>top=0.636620</tt>, <tt>bottom=-0.636620</tt>,
-<tt>max=1</tt>, <tt>min=-1</tt>, <tt>peak to peak=2</tt>, <tt>amplitude=1</tt>,
-<tt>pulse duration=0.5 s</tt> (duty 0.5), <tt>period=1 s</tt>, <tt>frequency=1 Hz</tt>. Over a
-2 M-sample window those two passes read about 0.1% of the samples.

src/help/11-math.txt

@@ -1,61 +0,0 @@
-<b>Math channels</b>
-
-A math channel is a signal computed from other signals. You build it as a small graph — source
-nodes, operations, one output — and udpscope then treats the result as an ordinary channel.
-
-<b>How to reach it</b>
-
-The math button in the toolbar, or <tt>g</tt>. The pane's <tt>+</tt> adds a channel, and opening
-one shows the graph editor: nodes as boxes, click a box to select it and edit its parameters beside
-the canvas. Inside the editor, <i>add node</i> is a menu button whose popover picks the op, so the
-node arrives as the operation you asked for.
-
-<b>Graph gestures:</b> <b>drag</b> from an output port to an input port to wire them; drag a
-wired input port off its connection to detach it; click a wire and press <tt>Delete</tt> to remove
-it; drag a box to move it. <b>Wheel</b> zooms about the pointer. <b>Drag the background</b> to
-pan. <tt>f</tt> fits all nodes into view; <tt>Ctrl+0</tt> resets the view. <i>tidy</i>, the button
-beside <i>fit</i> in the editor, lays the graph out in topological columns and frames it. The orange
-dot marks the output node; click <i>set as output</i> to move it.
-
-<b>Worth knowing</b>
-
-• The graph is evaluated as an ordered list, so a node may only read ones <i>above</i> it. A
-  wire drawn right to left re-sorts the list silently so the graph stays valid. A cycle is
-  unrepresentable: the connection is refused rather than created, and the line beneath the form
-  says why — a loop, or a node asked to read itself.
-• A derived channel <i>is</i> a channel. It appears in the signal panel, can be plotted,
-  measured, exported, and used as a source for another math channel.
-• The math runs on the <b>stored</b> samples — decimated and averaged — so a cutoff you type in
-  Hz means the rate the filter will actually run at. Change the window across a decimation
-  boundary and the coefficients are rebuilt for the new rate.
-• A source may only name an <i>acquired</i> channel. The stream's timestamp signal is not one:
-  a graph sourced from it validates and then reads NaN for ever, so the dropdown does not
-  offer it.
-• The output defaults to the <i>last</i> node, and a node added to a linear graph becomes the
-  output. Choosing an earlier node explicitly is respected.
-• Every numeric field starts at its own identity value — gain 1, offset 0 — not at the bottom
-  of its range.
-
-<b>Example</b>
-
-<tt>[sine] → [gain x2]</tt> gives a channel reading <tt>y=[-2, 2]</tt>. A 100 Hz low pass on the
-same source passes 50 Hz at 0.97 and 2 kHz at 0.002; a 1 kHz band pass with Q=2 passes 200 Hz at
-0.05, 1 kHz at 0.95 and 4 kHz at 0.05. Each derived channel must hold exactly as many samples as
-the shared clock has time slots.
-
-<b>Why an operation sometimes does nothing</b>. A graph's <i>output</i> is the node whose value
-becomes the channel, and it is drawn as the orange dot. A new graph is built source, then operation,
-and the last node added becomes the output -- but a graph whose output is left on the source is
-valid and simply passes its input through, which is the usual reason a gain or a filter appears to
-have no effect. <i>Set as output</i> moves the dot.
-
-<b>Apply is insensitive while the graph is incomplete.</b> A line beneath the form says why:
-an input that is not connected, no output chosen, or a <i>channel</i> node naming a signal the
-scope is not acquiring. Only the channels being acquired are offered, because a source that is not
-acquired reads as no data for ever — and a graph that reads NaN is harder to diagnose than one that
-would not save.
-
-<b>The filters are real filters.</b> A math channel's samples are produced as the stream arrives,
-once per stored slot, so a low pass carries the history a filter needs. A cutoff typed in hertz is
-against the <i>stored</i> rate, which is the wire rate until a wide window makes the buffer decimate
--- the status line's rate is that number, and the filters are rebuilt whenever it changes.

src/help/12-export.txt

@@ -1,33 +0,0 @@
-<b>Saving and export</b>
-
-Export writes the <i>visible range</i> of every plotted trace to a file: NumPy <tt>.npy</tt> or
-<tt>.csv</tt>, chosen by the extension you type.
-
-<b>How to reach it</b>
-
-<b>Export visible range…</b> in the overflow menu, or <tt>Ctrl+E</tt>. A file chooser asks where;
-the format follows the path's extension.
-
-<b>Worth knowing</b>
-
-• The table is collected at the moment you click, not when the chooser returns. A live view keeps
-  scrolling while a dialog is up, so a late collection would write a window you never saw.
-• The rows are the <b>stored samples</b>, never the LOD buckets the plot draws from. A row count
-  far below the span times the stored rate means something cut the table from the pyramid.
-• The stored rate is not always the wire rate. A window long enough to need decimation is stored
-  averaged at a lower rate, and the export carries <i>that</i> — read the status bar's ⓘ popover
-  for the figure before trusting a sample count.
-• Two time columns. <tt>time</tt> is the display timeline — negative ages ending at 0 while
-  streaming, offsets from the trigger edge while an event is held — so it is the x you read a
-  value at on screen. <tt>abs_seconds</tt> is the source's own clock for the same sample, which
-  is what lets two exports taken in different modes line up. Both are strictly increasing and
-  evenly spaced; duplicate or backwards stamps would mean the file held two clocks.
-• An export taken <i>mid-capture</i> writes the partly filled window that is on screen, which is
-  shorter than the event span. Export outside a capture if you want the whole event.
-
-<b>Example</b>
-
-A 2 s window at 10 kS/s over 3 traces writes 20001 rows and 5 columns
-(<tt>time</tt>, <tt>abs_seconds</tt>, three signals). The <tt>.npy</tt> is
-<tt>64·⌈(10+len(header)+1)/64⌉ + rows·(16 + 4·cols)</tt> bytes. Read it back with
-<tt>pd.DataFrame(np.load(path))</tt>.

src/help/13-sessions.txt

@@ -1,60 +0,0 @@
-<b>Sessions and settings</b>
-
-udpscope stores named sessions — <i>configurations</i> — per source, so reopening a source gives
-you the scope you closed, and one source can hold several arrangements for different experiments.
-There is no global preferences file: the session <i>is</i> the settings.
-
-<b>How to reach it</b>
-
-Nothing to open — the file is written as you work. Its path is in the About dialog, and the
-directory is <tt>$XDG_CONFIG_HOME/udpscope</tt>, or <tt>~/.config/udpscope</tt> when that is
-unset. Each source has a directory <tt>&lt;host&gt;_&lt;port&gt;/</tt> holding one
-<tt>&lt;name&gt;.toml</tt> per configuration and an <tt>active</tt> file naming the one it is on.
-
-<b>Configurations</b>
-
-<b>Configurations…</b> in the menu lists the running source's configurations: click a row to open
-it, <tt>×</tt> to delete it, or type a name and a note and press <i>Save this session</i> to keep
-the current arrangement under a new one. Opening a configuration saves the current session first,
-so switching never loses what it switches from.
-
-The startup chooser (start with no <tt>--server</tt>) lists one row per configuration, with its
-note and its settings, so two arrangements of one source are told apart before they open.
-
-A configuration also carries the settings that can only be decided when the buffers are
-allocated: the <b>buffer size</b> (<tt>--buffer-mb</tt>), relative time, and the packet capture's
-ring size. Opening a configuration from the chooser applies all three; switching inside a running
-app applies the rest and says in the status line that these take effect on the next start.
-
-The chooser's form sets the first two for a new host, and its pencil button edits them on an
-existing configuration — along with the name and the note. Renaming a configuration, or editing
-the address it points at, moves it: the old file is removed rather than left behind.
-
-<b>Worth knowing</b>
-
-• What a configuration persists: the time window, the rows and each row's slot signals, the
-  calibration, the trace colours, which signals are enabled, the math channels with their graphs,
-  the measurements pane — and the startup settings: buffer size, relative time and the packet
-  capture's ring size.
-• Signal identity is the <i>name</i> throughout, because a new CONFIG renumbers the channels.
-• A file written by a run against a source whose streamer was down would name no signals at all,
-  so such a run does <b>not</b> write: a configured session is never overwritten by a run that
-  configured nothing. (The chooser hides such a file for the same reason.)
-• The multicast group and the interface live <i>inside</i> the file, because its name cannot
-  carry them. A file from an older build has neither key and loads as unicast on the default
-  route.
-• The chooser lists only configurations that name at least one signal, which is what keeps it the
-  sessions you configured rather than every port you have ever tested against.
-• Deleting a configuration is a supported way to start over; the chooser's <tt>×</tt> and the
-  dialog's do exactly that.
-• A session from before configurations existed is imported once as the configuration
-  <tt>default</tt>, and the old file is kept beside the directory as
-  <tt>&lt;host&gt;_&lt;port&gt;.toml.imported</tt>.
-
-<b>Example</b>
-
-Connect to <tt>127.0.0.1:8000</tt>, drop three signals on row 1, set a 2 s window, and save the
-session as <tt>bench</tt> with a note. <tt>~/.config/udpscope/127.0.0.1_8000/bench.toml</tt> now
-holds <tt>window_s=2 comment="…"</tt> with <tt>signals = ["sine", "ramp", "noise", ""]</tt>, and
-the next run reports <tt>layout loaded from …/127.0.0.1_8000/bench.toml</tt> with those signals
-already acquired.

src/help/14-status.txt

@@ -1,46 +0,0 @@
-<b>Status bar and diagnostics</b>
-
-The status bar is two tiers. The bar itself is one glance line — the state, the rate and the
-window — and everything else is behind the ⓘ button at its right-hand end.
-
-<b>How to reach it</b>
-
-The bar is always visible under the plot. Click <b>ⓘ</b> for the detail popover.
-
-<b>Worth knowing</b>
-
-• The badge is one glyph in four colours: green <i>alternating</i> lit and dim means data is
-  arriving, and a steady colour means it is not. A badge that never blinks is not a working badge.
-  Of the two steady colours, <i>grey</i> is no stream at all or a pipeline you stopped (the
-  tooltip says which), and <i>yellow</i> is a source that answered but has sent no configuration.
-• The state field is one word from a fixed set: <tt>connecting</tt>, <tt>live</tt>,
-  <tt>paused</tt>, <tt>armed</tt>, <tt>capturing</tt>, <tt>event held</tt>, <tt>disarmed</tt>. Two
-  states add one field each: in trigger mode, how long ago the last event was; while paused, how
-  long you have been paused.
-• <tt>connecting</tt> means there is no <i>signal list</i> yet — either no session or a session
-  with no configuration behind it. Every other word claims a signal list, so until one arrives
-  there is nothing for them to describe: nothing can be enabled and no data is owed.
-• The paused figure is <i>wall</i> time, not stream time — the producer never stops while paused,
-  so it answers "how long have I been looking at this picture".
-• Nothing on the bar may change width with the stream, because the bar sits directly above the
-  plot and a wider label would relayout it. That is why the rate collapses to one figure or a
-  range rather than listing per channel, and why an elapsed time steps to a coarser unit instead
-  of growing digits.
-• <tt>gaps</tt> counts packets the receiver knows it missed. It is the number that matters: a
-  non-zero count means samples are absent from the buffer, not merely late.
-• <tt>reconnects</tt> counts sessions re-established with the source. Over unicast a climbing
-  count usually means a second client is taking the source's single session.
-• The starvation notice — <i>connected, but no data is arriving</i> — is that same situation seen
-  from the other side: the signal list is here, so something took the stream away. A source that
-  has sent <i>no</i> configuration gets a different notice, <i>trying to connect</i>, because
-  nothing was taken away — pointing the app at a port where nothing answers is that case, and the
-  usual cause is a streamer that is not running or is serving another port.
-• <tt>stored</tt> versus <tt>wire</tt> in the popover is the decimation. They differ exactly
-  when the window is too long to store at full rate.
-
-<b>Example</b>
-
-The bar reads <tt>● live · 10 kS/s · 2 s window</tt>. Behind ⓘ:
-<tt>Stream  connected, configured / packets 717 · frames 716 · gaps 0 / 3 signals · 3 channels</tt>,
-<tt>Buffer  200.0 MB · 1677 s span · time x1 / stored 10 kS/s (wire 10 kS/s)</tt>,
-<tt>Plot 1  3 traces · 195000 samples</tt>, <tt>Reconnects  0</tt>.

src/help/udpscope-help.gresource.xml

@@ -1,34 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<!--
-  SPDX-License-Identifier: MIT
-
-  The help pages, compiled into the binary for the same reason the icons are: udpscope is
-  run straight out of the build tree and has no install step, so a search path would have
-  to be located at runtime and the failure mode of not locating it is a help window full
-  of missing pages.
--->
-<gresources>
-  <gresource prefix="/org/udpscope/help">
-    <file>01-overview.txt</file>
-    <file>02-source.txt</file>
-    <file>03-signals.txt</file>
-    <file>04-layout.txt</file>
-    <file>05-window.txt</file>
-    <file>06-navigate.txt</file>
-    <file>07-pause.txt</file>
-    <file>08-trigger.txt</file>
-    <file>09-cursors.txt</file>
-    <file>10-measurements.txt</file>
-    <file>11-math.txt</file>
-    <file>12-export.txt</file>
-    <file>13-sessions.txt</file>
-    <file>14-status.txt</file>
-  
-    <!-- The screenshots live with the user documentation (docs/); the resource aliases
-         them under `img/` so a help page can name one by resource path. The path is relative
-         to this manifest's directory. -->
-    <file alias="img/main-window.png">../../docs/img/main-window.png</file>
-    <file alias="img/trigger-capture.png">../../docs/img/trigger-capture.png</file>
-    <file alias="img/math-editor.png">../../docs/img/math-editor.png</file>
-  </gresource>
-</gresources>

src/help_window.cpp

@@ -3,48 +3,36 @@
 
 #include <adwaita.h>
 
-#include <cstdio>
+#include <functional>
 #include <string>
+#include <vector>
 
 #include "build_info.hpp"
 #include "layout_store.hpp"
-#include "shortcuts.hpp"
+
+// Both come from CMakeLists: the document identifier is derived from the desktop file's
+// basename (its desktop-file id), and the directory is where the Mallard set lives in the
+// source tree, which is what the self-check scans. Yelp resolves `help:<identifier>` to
+// `<datadir>/help/<lang>/<identifier>/` on its own (freedesktop Help System Specification),
+// so the identifier and the installed directory have to name the same set -- which is why
+// neither is written out again here.
+static_assert(sizeof(UDPSCOPE_HELP_NAME) > 1, "UDPSCOPE_HELP_NAME must come from the build");
+static_assert(sizeof(UDPSCOPE_HELP_DIR) > 1, "UDPSCOPE_HELP_DIR must come from the build");
 
 namespace udpscope {
 namespace {
 
-/// Nulled by each window's own close handler, so a second open cannot present a dead widget.
-/// One pointer per window, file-scope because there is one application.
-///
-/// The help window and the shortcut overview are `GtkWindow`s. The About dialog is an
-/// `AdwDialog`, which is **not** a `GtkWindow`: it has no `::close-request`, so it clears on
-/// `::closed` and closes with `adw_dialog_close()`.
-GtkWidget* g_help = nullptr;
-/// The help window is a `.ui` file too, so its builder, the label one page's markup goes into and the
-/// column its screenshots go into are all kept beside the window's own pointer. All four are cleared by
-/// the window's own close handler: the page switch reads them, and it cannot run after the window is
-/// gone.
-GtkBuilder* g_help_ui = nullptr;
-GtkWidget* g_help_body = nullptr;
-GtkWidget* g_help_shots = nullptr;
+/// Nulled by each dialog's own close handler, so a second open cannot present a dead widget.
+/// One pointer per dialog, file-scope because there is one application. The help manual is no
+/// longer one of these: it opens in a separate viewer process through the `help:` URI, and a
+/// process with no window of ours has nothing to null.
 AdwDialog* g_about = nullptr;
-/// The overview is the one window here built from a `.ui` file, so its builder is held too: the window
-/// belongs to the builder, and a *destroyed* `GtkWindow` cannot be presented again -- which is why the
+/// The overview is built from a `.ui` file, so its builder is held too: the window belongs to
+/// the builder, and a *destroyed* `GtkWindow` cannot be presented again -- which is why the
 /// builder is replaced on the next opening rather than reused.
 GtkWidget* g_shortcuts = nullptr;
 GtkBuilder* g_shortcuts_ui = nullptr;
 
-/// The help window's own close handler, rather than the shared one: this window also owns the label a
-/// page is written into and the column its screenshots are built in, and a page switch that ran after
-/// the window was gone would read both.
-gboolean on_help_close(GtkWindow* window, gpointer) {
-  (void)window;
-  g_help = nullptr;
-  g_help_body = nullptr;
-  g_help_shots = nullptr;
-  return FALSE;  // let the default handler destroy it
-}
-
 gboolean on_window_close(GtkWindow* window, gpointer slot) {
   (void)window;
   *static_cast<GtkWidget**>(slot) = nullptr;
@@ -58,100 +46,58 @@ void on_dialog_closed(AdwDialog* dialog, gpointer slot) {
   *static_cast<AdwDialog**>(slot) = nullptr;
 }
 
-struct HelpPage {
-  const char* section;   ///< the group heading in the sidebar
-  const char* title;     ///< the row's label and the page's heading
-  const char* resource;  ///< a path under /org/udpscope/help
-  /// The screenshots shown above the text, as resource paths and a null terminator. A page
-  /// with none is the common case and the reason this is a list rather than one field: the
-  /// overview carries two, the window and a held capture.
-  const char* const* images = nullptr;
+/// What an asynchronous launch needs to survive the call: the window it is attributed to (held,
+/// because the call outlives the stack frame that made it) and the caller's reporter, if it asked
+/// for one. One small struct rather than two `gpointer`s, because a callback that takes both through
+/// one `user_data` still has to get them there.
+struct HelpLaunch {
+  GtkWindow* parent = nullptr;
+  std::function<void(bool, const std::string&)> done;
 };
 
-/// Adding a page is one .txt file, one <file> line in the manifest and one row here.
-/// The order here is the order the sidebar shows; `section` groups consecutive rows.
-/// How tall a page's screenshots are drawn. They are scaled to fit this *height* and centre
-/// themselves in it, so a 1500x950 capture is readable without a horizontal scrollbar.
-constexpr int kHelpShotHeight = 260;
-
-/// The screenshots each page carries, in the order it shows them.
-constexpr const char* kOverviewShots[] = {"/org/udpscope/help/img/main-window.png",
-                                          "/org/udpscope/help/img/trigger-capture.png",
-                                          nullptr};
-constexpr const char* kTriggerShots[] = {"/org/udpscope/help/img/trigger-capture.png",
-                                         nullptr};
-constexpr const char* kMathShots[] = {"/org/udpscope/help/img/math-editor.png", nullptr};
-
-constexpr HelpPage kPages[] = {
-    {"Getting started", "Overview", "/org/udpscope/help/01-overview.txt", kOverviewShots},
-    {"Getting started", "Choosing a source", "/org/udpscope/help/02-source.txt"},
-    {"Getting started", "Signals and calibration", "/org/udpscope/help/03-signals.txt"},
-    {"Getting started", "Rows, layout and drag & drop", "/org/udpscope/help/04-layout.txt"},
-    {"Viewing", "Time window", "/org/udpscope/help/05-window.txt"},
-    {"Viewing", "Navigating the plot", "/org/udpscope/help/06-navigate.txt"},
-    {"Viewing", "Pause and play", "/org/udpscope/help/07-pause.txt"},
-    {"Viewing", "Trigger", "/org/udpscope/help/08-trigger.txt", kTriggerShots},
-    {"Analysis", "Cursors", "/org/udpscope/help/09-cursors.txt"},
-    {"Analysis", "Measurements", "/org/udpscope/help/10-measurements.txt"},
-    {"Analysis", "Math channels", "/org/udpscope/help/11-math.txt", kMathShots},
-    {"Output and state", "Saving and export", "/org/udpscope/help/12-export.txt"},
-    {"Output and state", "Sessions and settings", "/org/udpscope/help/13-sessions.txt"},
-    {"Output and state", "Status bar and diagnostics", "/org/udpscope/help/14-status.txt"},
-};
-constexpr int kPageCount = static_cast<int>(sizeof(kPages) / sizeof(kPages[0]));
-
-/// The page's markup, or a one-line stand-in. `ok` reports whether the real body loaded
-/// *and* parsed: a missing resource and markup Pango rejects both render the stand-in,
-/// because a help window that fails to open is worse than one page that says so.
-std::string load_page(const HelpPage& page, bool* ok) {
-  *ok = false;
+/// The launch failed. Report it rather than leaving a click that silently did nothing -- and say
+/// *which* thing is missing: `gtk_uri_launcher_launch_finish()` reports that the URI could not be
+/// handed over, which is the handler's absence, while a document that is not installed is a
+/// different failure the launcher cannot tell it from. `help_installed_path()` settles that from the
+/// file system, so a missing *document* is not reported as a missing *handler*: with the manual
+/// installed the message names the viewer, and without it the message names the document, its
+/// expected path and the install command -- and a viewer as well, because that second possibility
+/// cannot be ruled out from here.
+void on_help_launched(GObject* source, GAsyncResult* result, gpointer user) {
+  auto* launch = static_cast<HelpLaunch*>(user);
   GError* error = nullptr;
-  GBytes* bytes = g_resources_lookup_data(page.resource, G_RESOURCE_LOOKUP_FLAGS_NONE,
-                                          &error);
-  if (bytes == nullptr) {
-    if (error != nullptr) g_error_free(error);
-    return "<i>This page is missing from the build.</i>";
-  }
-  gsize size = 0;
-  const char* data = static_cast<const char*>(g_bytes_get_data(bytes, &size));
-  std::string body(data, size);
-  g_bytes_unref(bytes);
-
-  if (!pango_parse_markup(body.c_str(), -1, 0, nullptr, nullptr, nullptr, &error)) {
-    if (error != nullptr) g_error_free(error);
-    return "<i>This page could not be displayed: its markup is malformed.</i>";
-  }
-  *ok = true;
-  return body;
-}
-
-void on_help_row_selected(GtkListBox*, GtkListBoxRow* row, gpointer) {
-  if (row == nullptr || g_help_body == nullptr) return;
-  const int idx = GPOINTER_TO_INT(g_object_get_data(G_OBJECT(row), "help-page"));
-  if (idx < 0 || idx >= kPageCount) return;
-  bool ok = false;
-  const std::string body = load_page(kPages[idx], &ok);
-  gtk_label_set_markup(GTK_LABEL(g_help_body), body.c_str());
-  // The screenshots above it, if this page has any. The column comes from the `.ui` by id rather than
-  // being found as the label's previous sibling: refilling it is a page *switch*, not a frame, so
-  // rebuilding it here is cheap and is also the only way to be sure the pictures are this page's and
-  // not the last one's.
-  GtkWidget* shots = g_help_shots;
-  if (shots != nullptr && GTK_IS_BOX(shots)) {
-    while (GtkWidget* old = gtk_widget_get_first_child(shots)) {
-      gtk_box_remove(GTK_BOX(shots), old);
+  const bool ok = gtk_uri_launcher_launch_finish(GTK_URI_LAUNCHER(source), result, &error);
+  if (!ok) {
+    const std::string installed = help_installed_path();
+    GtkAlertDialog* alert = gtk_alert_dialog_new("Could not open the help manual");
+    std::string detail = error != nullptr ? error->message : std::string("the launch failed");
+    detail += "\n\n";
+    if (!installed.empty()) {
+      detail += "The manual is installed at " + installed +
+                ", so what is missing is a viewer for the `help:` URI it is opened with: install "
+                "one (for example `yelp`) or make it the desktop's default for that scheme.";
+    } else {
+      // The system-wide install is named *first* on purpose: a set under the user's data
+      // directory is one a sandboxed viewer (Yelp) cannot read its figures from -- the pages
+      // open without their images -- so the no-root route carries that caveat rather than
+      // leading. The message is kept no longer than the one it replaces; do the same on edit.
+      detail += "The manual does not look installed: nothing named \"help:" UDPSCOPE_HELP_NAME
+                "\" was found where `help:` resolves. Install it system-wide:\n\n"
+                "    cmake -DCMAKE_INSTALL_PREFIX=/usr .. && sudo cmake --build build --target install-help\n\n"
+                "That writes where the viewer looks. The no-root `install-help-user` writes under "
+                "your data directory instead: a sandboxed viewer shows those pages without their "
+                "figures. A `help:` viewer (for example `yelp`) is needed as well.";
     }
-    for (const char* const* img = kPages[idx].images; img != nullptr && *img != nullptr; ++img) {
-      GtkWidget* shot = gtk_picture_new_for_resource(*img);
-      gtk_picture_set_can_shrink(GTK_PICTURE(shot), TRUE);
-      // A height, and `CONTAIN` (the default) to fit the image inside it: a picture that may
-      // shrink asks for no height at all in a box, so without this it is allocated nothing and
-      // the page shows its text with a gap where the screenshots should be.
-      gtk_widget_set_size_request(shot, -1, kHelpShotHeight);
-      gtk_box_append(GTK_BOX(shots), shot);
-    }
-    gtk_widget_set_visible(shots, gtk_widget_get_first_child(shots) != nullptr);
+    gtk_alert_dialog_set_detail(alert, detail.c_str());
+    gtk_alert_dialog_show(alert, launch->parent);
+    g_object_unref(alert);
   }
+  if (launch->done) {
+    launch->done(ok, ok || error == nullptr ? std::string() : std::string(error->message));
+  }
+  if (launch->parent != nullptr) g_object_unref(launch->parent);
+  delete launch;
+  if (error != nullptr) g_error_free(error);
 }
 
 }  // namespace
@@ -195,86 +141,81 @@ const char* about_icon_name() {
   return adw_about_dialog_get_application_icon(ADW_ABOUT_DIALOG(g_about));
 }
 
+std::string help_installed_path() {
+  // The freedesktop Help System Specification's own search order: `$XDG_DATA_HOME` first, then every
+  // `$XDG_DATA_DIRS` entry in order. Yelp resolves `help:<id>` the same way, so this is a reading of
+  // where the document *would* be found rather than a second, private convention.
+  std::vector<std::string> roots;
+  roots.emplace_back(g_get_user_data_dir() != nullptr ? g_get_user_data_dir() : "");
+  const char* const* dirs = g_get_system_data_dirs();
+  for (int i = 0; dirs != nullptr && dirs[i] != nullptr; ++i) roots.emplace_back(dirs[i]);
+  for (const std::string& root : roots) {
+    if (root.empty()) continue;
+    const std::string base = root + "/help";
+    GError* error = nullptr;
+    GDir* dir = g_dir_open(base.c_str(), 0, &error);
+    if (dir == nullptr) {
+      if (error != nullptr) g_error_free(error);
+      continue;
+    }
+    // `<lang>` is a directory of its own (`C`, `en`, `it`, ...), so the document is looked for one
+    // level below the `help` root rather than straight under it.
+    while (const char* lang = g_dir_read_name(dir)) {
+      const std::string candidate = base + "/" + lang + "/" UDPSCOPE_HELP_NAME;
+      if (g_file_test((candidate + "/index.page").c_str(), G_FILE_TEST_IS_REGULAR)) {
+        g_dir_close(dir);
+        return candidate;
+      }
+    }
+    g_dir_close(dir);
+  }
+  return std::string();
+}
+
 HelpReport help_self_check() {
   HelpReport report;
-  report.pages = kPageCount;
-  for (const HelpPage& page : kPages) {
-    bool ok = false;
-    const std::string body = load_page(page, &ok);
-    if (ok && !body.empty()) ++report.parsed;
-    if (report.shortest_title.empty() || body.size() < report.shortest_bytes) {
-      report.shortest_title = page.title;
-      report.shortest_bytes = body.size();
+
+  // The manual is a set of files on disk now, so the reading is a file-system one: a missing
+  // directory leaves `topics=0 index=false`, which is a manual that is not where the build
+  // says it is -- and Yelp would show nothing for `help:<identifier>`.
+  GError* error = nullptr;
+  GDir* dir = g_dir_open(UDPSCOPE_HELP_DIR, 0, &error);
+  if (dir == nullptr) {
+    if (error != nullptr) g_error_free(error);
+    return report;
+  }
+  while (const char* name = g_dir_read_name(dir)) {
+    if (!g_str_has_suffix(name, ".page")) continue;
+    if (g_strcmp0(name, "index.page") == 0) report.index = true;
+    else ++report.topics;
+  }
+  g_dir_close(dir);
+
+  // The figures the pages reference, counted for the same reason: an image that went missing
+  // is a broken figure in the viewer rather than a failed build.
+  const std::string figures = std::string(UDPSCOPE_HELP_DIR) + "/figures";
+  if (GDir* figdir = g_dir_open(figures.c_str(), 0, &error)) {
+    while (const char* name = g_dir_read_name(figdir)) {
+      if (g_str_has_suffix(name, ".png") || g_str_has_suffix(name, ".jpg")) ++report.figures;
     }
+    g_dir_close(figdir);
+  } else if (error != nullptr) {
+    g_error_free(error);
   }
   return report;
 }
 
-void show_help(GtkWindow* parent) {
-  if (g_help != nullptr) {
-    gtk_window_present(GTK_WINDOW(g_help));
-    return;
-  }
-
-  // A builder per opening, as with every other `.ui` here: the window belongs to its object list and
-  // `close-request` destroys the window, so the resource is parsed again rather than a dead window
-  // fetched. This is where the previous one goes, and it is safe because that window has been closed
-  // for as long as it takes someone to ask for help again.
-  g_clear_object(&g_help_ui);
-  g_help_ui = gtk_builder_new_from_resource("/org/udpscope/ui/help.ui");
-  if (g_help_ui == nullptr) return;
-  GObject* window = gtk_builder_get_object(g_help_ui, "help_window");
-  GObject* list = gtk_builder_get_object(g_help_ui, "page_list");
-  GObject* body = gtk_builder_get_object(g_help_ui, "body");
-  GObject* shots = gtk_builder_get_object(g_help_ui, "shot_box");
-  // A missing id is the one mistake the build and `GtkBuilder` both miss; every reader below would be a
-  // null widget on the first page switch.
-  if (window == nullptr || list == nullptr || body == nullptr || shots == nullptr) return;
-  g_help = GTK_WIDGET(window);
-  g_help_body = GTK_WIDGET(body);
-  g_help_shots = GTK_WIDGET(shots);
-  gtk_window_set_transient_for(GTK_WINDOW(g_help), parent);
-
-  // The rows are the pages, which is data and not template: a heading row per section, then one row per
-  // page carrying its own index. A template cannot know the fourteen pages, and a sectioned list is not
-  // what a GtkListView with one item factory can draw.
-  const char* current_section = nullptr;
-  for (int i = 0; i < kPageCount; ++i) {
-    if (current_section == nullptr || std::string(current_section) != kPages[i].section) {
-      current_section = kPages[i].section;
-      GtkWidget* heading = gtk_label_new(nullptr);
-      char markup[128];
-      std::snprintf(markup, sizeof(markup), "<b><small>%s</small></b>", current_section);
-      gtk_label_set_markup(GTK_LABEL(heading), markup);
-      gtk_label_set_xalign(GTK_LABEL(heading), 0.0f);
-      gtk_widget_set_margin_start(heading, 10);
-      gtk_widget_set_margin_top(heading, 10);
-      gtk_widget_set_margin_bottom(heading, 2);
-      GtkWidget* heading_row = gtk_list_box_row_new();
-      gtk_list_box_row_set_selectable(GTK_LIST_BOX_ROW(heading_row), FALSE);
-      gtk_list_box_row_set_activatable(GTK_LIST_BOX_ROW(heading_row), FALSE);
-      gtk_list_box_row_set_child(GTK_LIST_BOX_ROW(heading_row), heading);
-      gtk_list_box_append(GTK_LIST_BOX(list), heading_row);
-    }
-    GtkWidget* label = gtk_label_new(kPages[i].title);
-    gtk_label_set_xalign(GTK_LABEL(label), 0.0f);
-    gtk_widget_set_margin_start(label, 18);
-    gtk_widget_set_margin_end(label, 10);
-    gtk_widget_set_margin_top(label, 4);
-    gtk_widget_set_margin_bottom(label, 4);
-    GtkWidget* row = gtk_list_box_row_new();
-    gtk_list_box_row_set_child(GTK_LIST_BOX_ROW(row), label);
-    g_object_set_data(G_OBJECT(row), "help-page", GINT_TO_POINTER(i));
-    gtk_list_box_append(GTK_LIST_BOX(list), row);
-  }
-  g_signal_connect(list, "row-selected", G_CALLBACK(on_help_row_selected), nullptr);
-
-  // Select the first page so the window never opens blank.
-  GtkListBoxRow* first = gtk_list_box_get_row_at_index(GTK_LIST_BOX(list), 1);
-  if (first != nullptr) gtk_list_box_select_row(GTK_LIST_BOX(list), first);
-
-  g_signal_connect(g_help, "close-request", G_CALLBACK(on_help_close), &g_help);
-  gtk_window_present(GTK_WINDOW(g_help));
+void show_help(GtkWindow* parent, std::function<void(bool, const std::string&)> done) {
+  // The freedesktop `help:` URI, handed to whatever the desktop registered for it -- Yelp on
+  // GNOME. The launch is asynchronous, so both the parent and the reporter are carried across it in
+  // a heap `HelpLaunch` and released in the callback; `parent` may legitimately be nullptr (the
+  // chooser runs before any window exists).
+  auto* launch = new HelpLaunch;
+  launch->parent = parent != nullptr ? GTK_WINDOW(g_object_ref(parent)) : nullptr;
+  launch->done = std::move(done);
+  GtkUriLauncher* launcher = gtk_uri_launcher_new("help:" UDPSCOPE_HELP_NAME);
+  gtk_uri_launcher_launch(launcher, parent, nullptr, on_help_launched, launch);
+  g_object_unref(launcher);
 }
 
 void show_shortcuts(GtkWindow* parent) {
@@ -284,17 +225,16 @@ void show_shortcuts(GtkWindow* parent) {
   }
 
   // A `GtkShortcutsWindow` from `src/ui/shortcuts.ui` -- gedit's arrangement, and GTK's own: one
-  // section per page, with the sidebar and the search box drawn by the window itself.
-  //
-  // A UI file rather than widget construction because of the mouse rows. An accelerator cannot spell
-  // "Ctrl and drag", and libadwaita's `AdwShortcutsItem` -- the modern replacement for this widget --
-  // has no icon property at all, so its cell reads "No Shortcut". `GtkShortcutsShortcut`'s one generic
-  // gesture type draws the `icon` the row names, which is what puts a mouse glyph where the keycaps
-  // would be. (The widget is deprecated since 4.20, but this uses none of its functions: the file is
-  // loaded as data and presented as a `GtkWindow`, so the build stays at its four warnings.)
+  // section per page, with the sidebar and the search box drawn by the window itself. A UI file
+  // rather than widget construction because of the mouse rows: an accelerator cannot spell "Ctrl
+  // and drag", and libadwaita's `AdwShortcutsItem` -- the modern replacement -- has no icon
+  // property, so its cell reads "No Shortcut". `GtkShortcutsShortcut`'s one generic gesture type
+  // draws the `icon` the row names. (The widget is deprecated since 4.20, but this uses none of
+  // its functions: the file is loaded as data and presented as a `GtkWindow`.)
   //
   // A builder per opening, not one reused: the window belongs to the builder and `close-request`
-  // destroys the window, so the resource is parsed again rather than an already-dead window fetched.
+  // destroys the window, so the resource is parsed again rather than an already-dead window
+  // fetched.
   g_clear_object(&g_shortcuts_ui);
   g_shortcuts_ui = gtk_builder_new_from_resource("/org/udpscope/ui/shortcuts.ui");
   if (g_shortcuts_ui == nullptr) return;
@@ -307,7 +247,6 @@ void show_shortcuts(GtkWindow* parent) {
 }
 
 void close_help_windows() {
-  if (g_help != nullptr) gtk_window_close(GTK_WINDOW(g_help));
   if (g_about != nullptr) adw_dialog_close(g_about);
   if (g_shortcuts != nullptr) gtk_window_close(GTK_WINDOW(g_shortcuts));
 }

src/help_window.hpp

@@ -4,6 +4,7 @@
 #include <gtk/gtk.h>
 
 #include <cstddef>
+#include <functional>
 #include <string>
 
 namespace udpscope {
@@ -18,20 +19,39 @@ void show_about(GtkWindow* parent, const std::string& session_path);
 /// so the dialog is asserted to *show* the app icon rather than merely to open.
 const char* about_icon_name();
 
-/// The paged help window. Modal on nothing — it is a reference, so it stays usable while
-/// the scope runs. Already open: presented.
-void show_help(GtkWindow* parent);
+/// Opens the installed Mallard manual in the desktop help viewer — Yelp, through the
+/// `help:` URI the freedesktop Help System Specification defines — rather than drawing a
+/// window of our own. `parent` is the window the launch is attributed to (and the one an
+/// error is reported on); the viewer is a separate process, so nothing here can be closed
+/// with `close_help_windows()`.
+///
+/// `done`, when the caller gives one, is called with the *launch*'s outcome: whether the
+/// `help:` URI was handed to a viewer, and the error text when it was not. It says nothing
+/// about the viewer itself — that process may fail for its own reasons and this side cannot
+/// see them — so it is the self-check's reading of the path and not a promise that a window
+/// appeared. The failure alert is shown either way; the callback is an extra, not instead.
+void show_help(GtkWindow* parent, std::function<void(bool ok, const std::string& error)> done = {});
 
-/// What UDPSCOPE_PROBE_HELP_MS reports. `parsed` counts pages whose markup
-/// pango_parse_markup() accepted and whose body is non-empty; it must equal `pages`.
+/// Where `help:<id>` resolves to on this system: the first of `$XDG_DATA_HOME/help/<lang>/<id>/`
+/// and `$XDG_DATA_DIRS/help/<lang>/<id>/` that holds an `index.page`, or an empty string when no
+/// such directory does. This is the specification's own resolution, and the distinction a launch
+/// failure turns on: a missing *document* (install it) and a missing *handler* (install a viewer)
+/// are different problems with different fixes, and only the file system can tell them apart.
+std::string help_installed_path();
+
+/// What UDPSCOPE_PROBE_HELP_MS reports about the manual *in the tree*. `topics` is the
+/// number of `<id>.page` files other than `index.page`, and `index` says whether
+/// `index.page` is present: the manual is now a set of files on disk (installed by the
+/// `install()` rule, and read by Yelp), not a GResource in the binary, so the self-check
+/// asserts the set is *there* and must be read as a file-system finding — `topics=0
+/// index=0` means the manual is missing from `UDPSCOPE_HELP_DIR`.
 struct HelpReport {
-  int pages = 0;
-  int parsed = 0;
-  std::string shortest_title;
-  std::size_t shortest_bytes = 0;
+  int topics = 0;
+  bool index = false;
+  int figures = 0;
 };
 
-/// Loads and validates every page without building a window. Safe to call headless.
+/// Scans the manual's directory without opening a viewer. Safe to call headless.
 HelpReport help_self_check();
 
 /// The shortcut overview: the application accelerators and the plot's own interactions,
@@ -39,11 +59,11 @@ HelpReport help_self_check();
 /// deprecated as of GTK 4.18 and this project builds warning-free.
 void show_shortcuts(GtkWindow* parent);
 
-/// Closes whichever of the three windows are open. One of them is a GtkWindow -- the help
-/// window, closed with gtk_window_close(), which emits close-request so its handler runs. The
-/// other two are AdwDialogs, which are not GtkWindows: they close with adw_dialog_close(),
-/// which emits ::closed. Either way the file-scope pointer is nulled by the handler, which is
-/// what prevents a second open presenting a dead widget. Used by the probe.
+/// Closes whichever of the two dialogs are open. Both are `AdwDialog`s, which are not
+/// `GtkWindow`s: they close with `adw_dialog_close()`, which emits `::closed`, and the
+/// file-scope pointer is nulled by the handler that prevents a second open presenting a dead
+/// widget. There is no help window left to close -- the manual opens in a separate viewer
+/// process. Used by the probe.
 void close_help_windows();
 
 }  // namespace udpscope

src/icons/scalable/actions/udpscope-math-symbolic.svg

@@ -1,13 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<!-- SPDX-License-Identifier: MIT -->
-<!-- SPDX-FileCopyrightText: 2026 Martino Ferrari -->
-<!-- A sigma: the one pane that computes rather than reads. Four filled subpaths, all
-     wound clockwise so the default nonzero rule unions them where they overlap; the
-     diagonals run from the bars' left ends to a vertex right of centre, which is the
-     way the glyph actually points. -->
-<svg height="16px" width="16px" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg">
-  <path fill="#2e3436" d="M3 2 H13 V4 H3 Z
-                          M3 12 H13 V14 H3 Z
-                          M4.64 2.23 L10.64 7.23 L9.36 8.77 L3.36 3.77 Z
-                          M10.64 8.77 L4.64 13.77 L3.36 12.23 L9.36 7.23 Z"/>
-</svg>

src/icons/scalable/actions/udpscope-resize-cols-symbolic.svg

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!-- SPDX-License-Identifier: MIT -->
+<!-- SPDX-FileCopyrightText: 2026 Martino Ferrari -->
+<!-- A boundary that can be dragged sideways: a horizontal double-headed arrow, the turned twin of
+     udpscope-resize-rows-symbolic. It says *which* edge the handle moves, which a single chevron (a
+     "go next") does not. Every coordinate is a whole pixel of the 16px cell, every subpath is a filled
+     `path` wound the same way (a stroke would keep this colour on a dark theme), and the two heads
+     meet the shaft exactly, at y 5..11 and y 7..9. -->
+<svg height="16px" width="16px" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg">
+  <path fill="#2e3436" d="M4 7 H12 V9 H4 Z
+                          M1 8 L5 5 V11 Z
+                          M15 8 L11 11 V5 Z"/>
+</svg>

src/icons/scalable/actions/udpscope-trigger-symbolic.svg

@@ -1,16 +1,26 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!-- SPDX-License-Identifier: MIT -->
 <!-- SPDX-FileCopyrightText: 2026 Martino Ferrari -->
-<!-- A rising edge crossing a dashed trigger level: what the trigger *is*. The dash
-     rhythm is 2 on, 1 off (tight enough to read as one line rather than as a row of
-     dots), with the one wide gap at x 5..9 that the edge rises through. Every
-     coordinate is a whole pixel of the 16px cell so nothing blurs at 1x. -->
+<!-- The trigger: a sine and the dashed level it is looked for at, which is what a trigger *is* on a
+     waveform that is not a step. It used to be a rising edge, and one edge names only one of the four
+     shape triggers the panel offers — a wave crossing a level names the trigger's job instead. One
+     period, one-pixel stairs, the way the plot rasterises its own traces, with the level through the
+     centre so the crest and the trough stand clear and the crossings fall on the steep parts. Inset
+     two pixels, like the tabs' glyphs, so no art is flush with an edge a button might clip. -->
 <svg height="16px" width="16px" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg">
-  <path fill="#2e3436" d="M0 11 H8 V13 H0 Z
-                          M6 3 H8 V13 H6 Z
-                          M6 3 H16 V5 H6 Z
-                          M0 7 H2 V9 H0 Z
-                          M3 7 H5 V9 H3 Z
-                          M9 7 H11 V9 H9 Z
-                          M12 7 H14 V9 H12 Z"/>
+  <path fill="#2e3436" d="M2 7 H3 V10 H2 Z
+                          M3 5 H4 V8 H3 Z
+                          M4 3 H5 V6 H4 Z
+                          M5 3 H6 V6 H5 Z
+                          M6 4 H7 V7 H6 Z
+                          M7 6 H8 V9 H7 Z
+                          M8 8 H9 V11 H8 Z
+                          M9 10 H10 V13 H9 Z
+                          M10 11 H11 V14 H10 Z
+                          M11 11 H12 V14 H11 Z
+                          M12 9 H13 V12 H12 Z
+                          M13 7 H14 V10 H13 Z
+                          M2 7 H5 V9 H2 Z
+                          M7 7 H10 V9 H7 Z
+                          M11 7 H14 V9 H11 Z"/>
 </svg>

src/icons/udpscope.gresource.xml

@@ -20,9 +20,9 @@
     <file preprocess="xml-stripblanks">scalable/actions/udpscope-trigger-symbolic.svg</file>
     <file preprocess="xml-stripblanks">scalable/actions/udpscope-cursors-symbolic.svg</file>
     <file preprocess="xml-stripblanks">scalable/actions/udpscope-measure-symbolic.svg</file>
-    <file preprocess="xml-stripblanks">scalable/actions/udpscope-math-symbolic.svg</file>
     <file preprocess="xml-stripblanks">scalable/actions/udpscope-events-symbolic.svg</file>
     <file preprocess="xml-stripblanks">scalable/actions/udpscope-resize-rows-symbolic.svg</file>
+    <file preprocess="xml-stripblanks">scalable/actions/udpscope-resize-cols-symbolic.svg</file>
     <file preprocess="xml-stripblanks">scalable/apps/org.udpscope.app.svg</file>
     <file preprocess="xml-stripblanks">scalable/apps/org.udpscope.app-symbolic.svg</file>
   </gresource>

src/layout_store.cpp

@@ -4,6 +4,7 @@
 #include "layout_store.hpp"
 
 #include <algorithm>
+#include <cmath>
 #include <cstdint>
 #include <cstdio>
 #include <cstdlib>
@@ -55,12 +56,23 @@ namespace {
 std::string toml_escape(const std::string& s) {
   std::string out = "\"";
   for (char c : s) {
-    if (c == '"' || c == '\\') out.push_back('\\');
-    out.push_back(c);
+    // The file is read line by line, so a raw newline in a value would end the line early.
+    if (c == '\n') {
+      out += "\\n";
+    } else if (c == '\r') {
+      out += "\\r";
+    } else {
+      if (c == '"' || c == '\\') out.push_back('\\');
+      out.push_back(c);
+    }
   }
   return out + "\"";
 }
 
+/// The character an escape `\x` stands for: `\n` and `\r` are the two line breaks, anything else
+/// (the quote, the backslash) stands for itself.
+char unescaped(char c) { return c == 'n' ? '\n' : c == 'r' ? '\r' : c; }
+
 bool unescape(std::string& s) {
   std::string out;
   for (std::size_t i = 0; i < s.size(); ++i) {
@@ -69,8 +81,8 @@ bool unescape(std::string& s) {
       continue;
     }
     if (++i >= s.size()) return false;
-    if (s[i] == '"' || s[i] == '\\') {
-      out.push_back(s[i]);
+    if (s[i] == '"' || s[i] == '\\' || s[i] == 'n' || s[i] == 'r') {
+      out.push_back(unescaped(s[i]));
     } else {
       return false;
     }
@@ -317,11 +329,15 @@ std::vector<KnownSource> known_sources() {
       s.port = port;
       s.config = name;
       s.comment = st.comment;
-      s.buffer_mb = st.buffer_mb;
+      s.buffer_samples = st.buffer_samples;
       s.relative_time = st.relative_time;
       s.capture_packets = st.capture_packets;
       s.multicast = st.multicast;
       s.interface_addr = st.interface_addr;
+      if (!st.source_kind.empty()) {
+        s.kind = st.source_kind;
+        s.opts = st.source_opts;
+      }
       s.rows = static_cast<int>(st.rows.size());
       for (const LayoutState::Row& row : st.rows) {
         for (const std::string& sig : row.signals) {
@@ -332,7 +348,7 @@ std::vector<KnownSource> known_sources() {
       // session file per probe run and every one holds `signals = ["", "", "", ""]`. One that
       // carries a *setting* is worth a row even before it has ever streamed -- that is how a host is
       // set up from the chooser's form, and the settings are the whole point of editing one.
-      const bool configured = s.signals > 0 || s.buffer_mb > 0.0 || !st.comment.empty() ||
+      const bool configured = s.signals > 0 || s.buffer_samples > 0 || !st.comment.empty() ||
                               st.relative_time || st.capture_packets > 0;
       if (!configured) continue;
       struct stat fb {};
@@ -424,6 +440,7 @@ bool load_layout(const std::string& path, LayoutState& out) {
   st.window_s = 0.0;
   st.rows.clear();
   st.calibration.clear();
+  st.units.clear();
   st.colors.clear();
   st.enabled.clear();
   st.math.clear();
@@ -431,7 +448,7 @@ bool load_layout(const std::string& path, LayoutState& out) {
 
   std::string line;
   // What the last `[[...]]` header opened, so keys land in the right record.
-  enum class Section { Top, Plot, Calibration, Color, Math, Measure } section = Section::Top;
+  enum class Section { Top, Plot, Calibration, Unit, Color, Math, Measure } section = Section::Top;
   int plot_count = 0;
   bool plot_section_seen = false;
   while (std::getline(in, line)) {
@@ -445,6 +462,9 @@ bool load_layout(const std::string& path, LayoutState& out) {
       } else if (t == "[[calibration]]") {
         section = Section::Calibration;
         st.calibration.emplace_back();
+      } else if (t == "[[unit]]") {
+        section = Section::Unit;
+        st.units.emplace_back();
       } else if (t == "[[color]]") {
         section = Section::Color;
         st.colors.emplace_back();
@@ -468,14 +488,71 @@ bool load_layout(const std::string& path, LayoutState& out) {
         std::string s = v.substr(1, v.size() - 2);
         std::string out;
         for (std::size_t i = 0; i < s.size(); ++i) {
-          if (s[i] == '\\' && i + 1 < s.size()) ++i;
-          out.push_back(s[i]);
+          if (s[i] == '\\' && i + 1 < s.size()) {
+            out.push_back(unescaped(s[++i]));
+          } else {
+            out.push_back(s[i]);
+          }
         }
         return out;
       }
       return v;
     };
 
+    /// One `trigger_*` key, by its name after the prefix. Text for the two enumerations and for the
+    /// signal, numbers for the rest; `value` arrives unquoted.
+    const auto trigger_key = [](LayoutState::Trigger& t, const std::string& k, const std::string& v) {
+      const auto num = [&](double& out) {
+        try {
+          out = std::stod(v);
+        } catch (...) {
+        }
+      };
+      if (k == "enabled") {
+        t.enabled = v == "true";
+      } else if (k == "signal") {
+        t.channel = v;
+      } else if (k == "type") {
+        t.type = v;
+      } else if (k == "edge") {
+        t.edge = v;
+      } else if (k == "cmp") {
+        t.cmp = v;
+      } else if (k == "mode") {
+        t.mode = v;
+      } else if (k == "level") {
+        num(t.level);
+        t.level_given = true;
+      } else if (k == "level2") {
+        num(t.level2);
+      } else if (k == "width") {
+        num(t.width_s);
+      } else if (k == "width2") {
+        num(t.width2_s);
+      } else if (k == "timeout") {
+        num(t.timeout_s);
+      } else if (k == "pre") {
+        num(t.pretrigger_pct);
+      } else if (k == "holdoff") {
+        num(t.holdoff_s);
+      } else if (k == "band") {
+        num(t.noise_band);
+      } else if (k == "hf") {
+        num(t.hf_fc);
+      } else if (k == "persistence") {
+        double n = 0.0;
+        num(n);
+        t.persistence = static_cast<int>(n);
+      } else if (k == "density") {
+        t.density = v == "true";
+      } else if (k == "density_decay") {
+        t.density_decay = v == "time" ? "time" : "acquisitions";
+      } else if (k == "density_tau") {
+        num(t.density_tau_s);
+      } else if (k == "density_factor") {
+        num(t.density_factor);
+      }
+    };
     if (section == Section::Top) {
       if (key == "window_s") {
         try {
@@ -496,15 +573,26 @@ bool load_layout(const std::string& path, LayoutState& out) {
         }
       } else if (key == "measure_stats") {
         st.measure_stats = value == "true";
+      } else if (key == "dock") {
+        st.dock_shown = value == "true";
+      } else if (key.rfind("trigger_", 0) == 0) {
+        trigger_key(st.trigger, key.substr(8), strip_quote(value));
       } else if (key == "multicast") {
         st.multicast = strip_quote(value);
       } else if (key == "interface") {
         st.interface_addr = strip_quote(value);
+      } else if (key == "source_kind") {
+        st.source_kind = strip_quote(value);
+      } else if (key.rfind("source_opt_", 0) == 0) {
+        const std::string k = key.substr(11);
+        if (SourceConfig::valid_key(k)) st.source_opts.set(k, strip_quote(value));
       } else if (key == "comment") {
         st.comment = strip_quote(value);
-      } else if (key == "buffer_mb") {
+      } else if (key == "buffer_samples") {
         try {
-          st.buffer_mb = std::stod(value);
+          // A negative or absurd count is "not stored", not a request: `stoull` wraps a minus sign.
+          const unsigned long long n = value.find('-') == std::string::npos ? std::stoull(value) : 0;
+          st.buffer_samples = n >= 128 && n <= 1000000000000ull ? n : 0;
         } catch (...) {
         }
       } else if (key == "relative_time") {
@@ -524,6 +612,15 @@ bool load_layout(const std::string& path, LayoutState& out) {
         st.rows.back().signals = names;
       } else if (key == "weight") {
         st.rows.back().weight = std::strtod(value.c_str(), nullptr);
+      } else if (key == "row") {
+        try {
+          const int r = std::stoi(value);
+          if (r >= 0) st.rows.back().row = r;
+        } catch (...) {
+        }
+      } else if (key == "width") {
+        const double w = std::strtod(value.c_str(), nullptr);
+        if (std::isfinite(w) && w > 0.0) st.rows.back().width = w;
       }
     } else if (section == Section::Math && !st.math.empty()) {
       MathChannel& m = st.math.back();
@@ -566,6 +663,14 @@ bool load_layout(const std::string& path, LayoutState& out) {
           m.options.threshold_pct = std::stod(value);
         } catch (...) {
         }
+      } else if (key == "threshold2") {
+        // The band's other edge. A file written before `Between` existed has no such key, and the
+        // struct's own default is what such a measurement then reads -- which is the same value the
+        // dialog offers a new one.
+        try {
+          m.options.threshold_pct2 = std::stod(value);
+        } catch (...) {
+        }
       } else if (key == "noise") {
         try {
           m.options.noise_pct = std::stod(value);
@@ -595,6 +700,12 @@ bool load_layout(const std::string& path, LayoutState& out) {
         } catch (...) {
         }
       }
+    } else if (section == Section::Unit && !st.units.empty()) {
+      if (key == "name") {
+        st.units.back().name = strip_quote(value);
+      } else if (key == "unit") {
+        st.units.back().unit = strip_quote(value);
+      }
     } else if (section == Section::Color && !st.colors.empty()) {
       if (key == "name") {
         st.colors.back().name = strip_quote(value);
@@ -633,6 +744,12 @@ bool save_layout(const std::string& path, const LayoutState& state) {
   if (!state.interface_addr.empty()) {
     o << "interface = " << toml_escape(state.interface_addr) << "\n";
   }
+  if (!state.source_kind.empty() && state.source_kind != "udps") {
+    o << "source_kind = " << toml_escape(state.source_kind) << "\n";
+    for (const auto& kv : state.source_opts.items()) {
+      o << "source_opt_" << kv.first << " = " << toml_escape(kv.second) << "\n";
+    }
+  }
   // Top level, before any table. Emitted after the `[[calibration]]` tables it belonged to the last
   // of them -- a bare key after a header is that table's key in TOML -- so the parser, correctly,
   // never saw it and a session's enable state was silently lost.
@@ -645,12 +762,43 @@ bool save_layout(const std::string& path, const LayoutState& state) {
     o << "]\n";
   }
   o << "measure_stats = " << (state.measure_stats ? "true" : "false") << "\n";
+  o << "dock = " << (state.dock_shown ? "true" : "false") << "\n";
+  // The trigger, settings and state both. Written even when it is off: that is the point of it.
+  o << "trigger_enabled = " << (state.trigger.enabled ? "true" : "false") << "\n";
+  if (!state.trigger.channel.empty()) {
+    o << "trigger_signal = " << toml_escape(state.trigger.channel) << "\n";
+  }
+  o << "trigger_type = " << toml_escape(state.trigger.type) << "\n";
+  o << "trigger_edge = " << toml_escape(state.trigger.edge) << "\n";
+  o << "trigger_cmp = " << toml_escape(state.trigger.cmp) << "\n";
+  o << "trigger_mode = " << toml_escape(state.trigger.mode) << "\n";
+  o << "trigger_level = " << state.trigger.level << "\n";
+  o << "trigger_level2 = " << state.trigger.level2 << "\n";
+  o << "trigger_width = " << state.trigger.width_s << "\n";
+  o << "trigger_width2 = " << state.trigger.width2_s << "\n";
+  o << "trigger_timeout = " << state.trigger.timeout_s << "\n";
+  o << "trigger_pre = " << state.trigger.pretrigger_pct << "\n";
+  o << "trigger_holdoff = " << state.trigger.holdoff_s << "\n";
+  o << "trigger_band = " << state.trigger.noise_band << "\n";
+  o << "trigger_hf = " << state.trigger.hf_fc << "\n";
+  o << "trigger_persistence = " << state.trigger.persistence << "\n";
+  // The phosphor density, the display that is an image rather than a set of traces. Its four fields
+  // are written whether or not it is on, like every other trigger setting: a display set up once and
+  // switched off is still the display you come back to.
+  o << "trigger_density = " << (state.trigger.density ? "true" : "false") << "\n";
+  o << "trigger_density_decay = " << toml_escape(state.trigger.density_decay) << "\n";
+  o << "trigger_density_tau = " << state.trigger.density_tau_s << "\n";
+  o << "trigger_density_factor = " << state.trigger.density_factor << "\n";
   if (!state.comment.empty()) o << "comment = " << toml_escape(state.comment) << "\n";
-  if (state.buffer_mb > 0.0) o << "buffer_mb = " << state.buffer_mb << "\n";
+  if (state.buffer_samples > 0) o << "buffer_samples = " << state.buffer_samples << "\n";
   o << "relative_time = " << (state.relative_time ? "true" : "false") << "\n";
   if (state.capture_packets > 0) o << "capture_packets = " << state.capture_packets << "\n";
   for (const auto& row : state.rows) {
-    o << "\n[[plot]]\nweight = " << row.weight << "\nsignals = [";
+    o << "\n[[plot]]\n";
+    // A row of -1 is a state built without the split (nothing in the app does that now); leaving the
+    // key out keeps it readable as the one-cell-per-row file it is.
+    if (row.row >= 0) o << "row = " << row.row << "\nwidth = " << row.width << "\n";
+    o << "weight = " << row.weight << "\nsignals = [";
     for (std::size_t i = 0; i < row.signals.size(); ++i) {
       if (i != 0) o << ", ";
       o << toml_escape(row.signals[i]);
@@ -661,6 +809,9 @@ bool save_layout(const std::string& path, const LayoutState& state) {
     o << "\n[[calibration]]\nname = " << toml_escape(cal.name) << "\ngain = " << cal.gain
       << "\noffset = " << cal.offset << "\n";
   }
+  for (const auto& u : state.units) {
+    o << "\n[[unit]]\nname = " << toml_escape(u.name) << "\nunit = " << toml_escape(u.unit) << "\n";
+  }
   for (const auto& color : state.colors) {
     char rgb[16];
     std::snprintf(rgb, sizeof(rgb), "\"#%06X\"", color.rgb & 0x00FFFFFFu);
@@ -687,6 +838,7 @@ bool save_layout(const std::string& path, const LayoutState& state) {
     }
     o << "\n[[measure]]\nsignal = " << toml_escape(m.signal) << "\ntype = " << kind
       << "\nthreshold = " << m.options.threshold_pct
+      << "\nthreshold2 = " << m.options.threshold_pct2
       << "\nabove = " << (m.options.above ? "true" : "false") << "\nshow = "
       << (m.options.show_on_plot ? "true" : "false") << "\nnoise = " << m.options.noise_pct
       << "\nhf = " << m.options.hf_fc << "\n";

src/layout_store.hpp

@@ -8,6 +8,7 @@
 
 #include "math_channel.hpp"
 #include "measure.hpp"
+#include "source/source_config.hpp"
 
 namespace udpscope {
 
@@ -23,6 +24,13 @@ struct LayoutState {
     /// The row's share of the figure's height, 1 for equal rows. Part of the layout because a sizing a
     /// user dragged is an arrangement, and an arrangement that is not saved is one that is lost.
     double weight = 1.0;
+    /// The figure row this plot sits in; plots of one row are the cells of a horizontal split, in
+    /// order. -1 means the file had no `row` key (a session from before the split), which loads as
+    /// one cell per row.
+    int row = -1;
+    /// This cell's share of its row's width, 1 for equal cells. `weight` is the *row's* and is
+    /// written on every cell of the row; `width` is the cell's own.
+    double width = 1.0;
   };
 
   double window_s = 0.0;  ///< 0 keeps the default window
@@ -35,6 +43,13 @@ struct LayoutState {
   };
   std::vector<Calibration> calibration;
 
+  /// The unit names the user gave streamed signals, by signal name. Only the overrides.
+  struct Unit {
+    std::string name;
+    std::string unit;
+  };
+  std::vector<Unit> units;
+
   /// The trace colours the user chose, `0xRRGGBB`. Only the *overrides*: a signal with no entry
   /// takes the positional palette entry, which is what keeps a stream's new signals coloured
   /// without a session having to name them. Saved by name like every identity here.
@@ -54,6 +69,12 @@ struct LayoutState {
   /// unicast; empty `interface_addr` is the default route.
   std::string multicast;
   std::string interface_addr;
+  /// Which source kind this session belongs to. Empty means `udps`: every file written before the
+  /// plugins existed. Only a kind other than `udps` is written, so a UDPS session file is
+  /// byte-identical to what earlier versions wrote.
+  std::string source_kind;
+  /// That kind's settings (`SourceConfig`), stored as top-level `source_opt_<key>` entries.
+  SourceConfig source_opts;
 
   /// The derived channels, graphs and all: the editor's work is part of the session, not of the
   /// process. A graph is stored as one string per node so the file stays in this store's TOML
@@ -66,9 +87,64 @@ struct LayoutState {
   /// stream and mean nothing restored against another one.
   bool measure_stats = false;
 
+  /// The dock's shown state (the user's last word on the toolbar's Dock button). The one thing the dock
+  /// persists -- its 320 px width is the `.ui`'s. An older file's `side_tab` key is not read: the parser
+  /// ignores keys it does not know.
+  bool dock_shown = true;
+
   /// The measurements pane, by signal *name* and with the type and options a row was built with.
   std::vector<Measure> measures;
 
+  /// The trigger: its settings *and* whether trigger mode was on. Both, and the settings even while
+  /// it is off, because a trigger set up once and switched off is still the trigger you come back to
+  /// -- and the pane's locked view is built from exactly this.
+  ///
+  /// The signal and the two enumerations are stored as *text*: the signal by name, because every
+  /// rebuild renumbers the channels (the model's own rule), and the shapes by the words the panel's
+  /// dropdowns show, because an index would tie this file to a declaration order -- which the math
+  /// channel's op index already taught this store once.
+  struct Trigger {
+    bool enabled = false;
+    std::string channel;                ///< the acquired channel's name; empty is "none chosen"
+    std::string type = "edge";          ///< edge | pulse width | window | dropout
+    std::string edge = "rising";        ///< rising | falling | both
+    std::string cmp = "greater";        ///< pulse width: `<` | `>` | within | outside
+    std::string mode = "normal";        ///< normal | single
+    double level = 0.0;
+    double level2 = 0.0;                ///< window: the band's other edge
+    double width_s = 1.0e-3;
+    double width2_s = 2.0e-3;
+    double timeout_s = 1.0e-3;
+    double pretrigger_pct = 50.0;
+    double holdoff_s = 0.010;
+    double noise_band = 0.0;
+    double hf_fc = 0.0;
+    /// How many of the most recent acquisitions the trigger mode keeps on screen (1 = the event
+    /// alone). Part of the trigger's own setup, like the window it captures and the shape it waits
+    /// for: it is what the display does with the acquisitions, and there is no second switch.
+    ///
+    /// This is the **multiple event** display -- N retained acquisitions, drawn as N traces. The
+    /// phosphor density beside it is a different display with a different cost (one bounded image a
+    /// trace against N window copies), which is why it has its own four fields below and why this
+    /// one keeps the key it has always had: an older file's `trigger_persistence` is still the
+    /// multiple-event depth.
+    int persistence = 1;
+    /// The **phosphor density** (`TriggerConfig::density` and the three beside it): whether the
+    /// trigger-mode display accumulates every acquisition into one image, what it fades by, and the
+    /// constant or factor that fade uses. Persisted because it is a display the user set up and
+    /// comes back to -- the trigger settings around it already are.
+    bool density = false;
+    /// "acquisitions" | "time": the same two words the panel's dropdown shows, for the reason the
+    /// shapes above are stored as text -- an index would tie the file to a declaration order.
+    std::string density_decay = "acquisitions";
+    double density_tau_s = 1.0;
+    double density_factor = 0.5;
+    /// Whether the file said anything about the level. A session that did keeps it; one that did not
+    /// leaves the panel's own "follow the channel's range" default alone.
+    bool level_given = false;
+  };
+  Trigger trigger;
+
   /// Free text the user attached to this configuration: what it is for, what to look at first.
   /// A configuration is a *named* session, and the name alone rarely says what makes it different
   /// from its neighbour.
@@ -77,9 +153,12 @@ struct LayoutState {
   /// The startup settings the configuration carries, applied when the chooser opens it -- which is
   /// why they live here and not only on the command line: two sources on one machine want different
   /// buffers and different clocks, and retyping the flags to look at the second one is how a
-  /// setting gets forgotten. A zero `buffer_mb` and an empty `capture_packets` mean "not stored":
-  /// the command line's value stands, so an old file cannot silently shrink a buffer.
-  double buffer_mb = 0.0;
+  /// setting gets forgotten. A zero `buffer_samples` and an empty `capture_packets` mean "not stored":
+  /// the command line's value stands, so an old file cannot silently shrink a buffer. The budget is
+  /// samples per acquired signal (the memory limit is the application's, not a source's). A file from
+  /// before that unit carries `buffer_mb`, which is not read: it reads as "not stored" and the
+  /// default stands, rather than a megabyte count being taken for a sample count.
+  std::uint64_t buffer_samples = 0;
   bool relative_time = false;
   std::uint32_t capture_packets = 0;
 };
@@ -90,6 +169,8 @@ struct KnownSource {
   std::uint16_t port = 0;
   std::string multicast;       ///< empty = unicast
   std::string interface_addr;  ///< empty = the default route
+  std::string kind = "udps";   ///< the session's source kind
+  SourceConfig opts;           ///< that kind's settings (empty for UDPS, whose fields are above)
   int rows = 0;                ///< plots the session had
   int signals = 0;             ///< named slots across those plots
   std::int64_t mtime = 0;      ///< orders the list; never shown
@@ -98,7 +179,7 @@ struct KnownSource {
   std::string config;
   std::string comment;         ///< the configuration's note, shown beside its name
   /// The startup settings this configuration carries, so the chooser can apply them.
-  double buffer_mb = 0.0;
+  std::uint64_t buffer_samples = 0;
   bool relative_time = false;
   std::uint32_t capture_packets = 0;
 };

src/main.cpp

@@ -7,36 +7,69 @@
 #include "waveform.hpp"
 #include "model.hpp"
 #include "plot_host.hpp"
+#include "source/registry.hpp"
 #include "source_dialog.hpp"
 #include "ui.hpp"
 
+#include <glib.h>
+
 #include <cstdio>
 #include <exception>
 
 int main(int argc, char** argv) {
   udpscope::Config cfg;
   try {
+    udpscope::register_builtin_sources();
     cfg = udpscope::parse_args(argc, argv);
     // The preferences fill in what the command line did not decide. `--relative-time` is an explicit
     // instruction for this run, so a preference can only turn the mode on, never off -- which is also
     // why this is read here, before the buffers are planned: the mode changes how they are filled.
-    if (udpscope::load_settings().relative_time) cfg.relative_time = true;
+    const udpscope::Settings prefs = udpscope::load_settings();
+    if (prefs.relative_time) cfg.relative_time = true;
+    // The memory limit is the same kind of statement, the other way round: the flag is the explicit
+    // instruction for this run and the preference only fills in when it was absent.
+    if (!cfg.memory_limit_specified) cfg.memory_limit_mb = static_cast<std::uint64_t>(prefs.memory_limit_mb);
   } catch (const std::exception& e) {
     std::fprintf(stderr, "udpscope: %s\n", e.what());
     return 2;
   }
 
+  // `--renderer` is exported here and nowhere else, because GSK reads `GSK_RENDERER` when it
+  // *creates* its renderer: inside the first `adw_init()`/`gtk_init()`, which `choose_source()`
+  // below may call. Setting it after that point is a silent no-op, so the one place it can be
+  // honoured is before anything touches GTK. Overwrite: a flag on the command line is a
+  // statement about this run, and the environment is only a default it may override.
+  //
+  // `cairo` is the whole software preset and not just GSK's half: the plot is a `GtkGLArea`,
+  // which asks GDK for a GL context of its own whatever GSK draws with. Over X11 forwarding
+  // that request is what leaves the window unallocated (no `buffer allocated:` line, zero
+  // width) once the Vulkan swapchain failure is out of the way, so `LIBGL_ALWAYS_SOFTWARE`
+  // makes Mesa answer it with llvmpipe. This is the pair `tools/make-help-shots.sh` sets.
+  if (!cfg.renderer.empty()) g_setenv("GSK_RENDERER", cfg.renderer.c_str(), TRUE);
+  if (cfg.renderer == "cairo") g_setenv("LIBGL_ALWAYS_SOFTWARE", "1", TRUE);
+  // The startup half of the renderer probe, printed before GTK exists: the request and the
+  // variables this process actually exported. The window's `[renderer] realized=` line is the
+  // other half and says which renderer GTK built.
+  if (g_getenv("UDPSCOPE_PROBE_RENDERER") != nullptr) {
+    const char* gsk = g_getenv("GSK_RENDERER");
+    const char* gl = g_getenv("LIBGL_ALWAYS_SOFTWARE");
+    std::fprintf(stderr, "[renderer] option=%s GSK_RENDERER=%s LIBGL_ALWAYS_SOFTWARE=%s\n",
+                 cfg.renderer.empty() ? "(unset)" : cfg.renderer.c_str(),
+                 gsk != nullptr ? gsk : "(unset)", gl != nullptr ? gl : "(unset)");
+    std::fflush(stderr);
+  }
+
   // No `--server` means the user has not said which source to open, so ask. Before the model:
   // declining must cost no buffer and no socket, and nothing below has to cope with "no source".
   // `--open` is the other answer to that question, and the chooser knows it: its Waveforms page
   // fills `open_waveform` in instead of the connection fields.
-  const bool asked = !cfg.server_specified && cfg.open_waveform.empty();
+  const bool asked = !cfg.has_source() && cfg.open_waveform.empty();
   if (asked && !udpscope::choose_source(cfg)) return 0;
   // A source named on the command line skips the chooser, but its *stored* configuration still
   // applies: the buffer size, the clock and the capture ring are decided here, before the model --
   // which is the only moment they can be -- and a saved host whose buffer was ignored because the
   // address came from the command line is an edit that looks like it never took effect.
-  if (cfg.server_specified) udpscope::apply_stored_settings(cfg);
+  if (cfg.has_source()) udpscope::apply_stored_settings(cfg);
 
   // Everything from here to `gtk_window_present()` inside `run_ui()` runs with no main loop: the
   // buffer is allocated, a recording is read, then the whole UI is built. The chooser's window is

src/measure.cpp

@@ -14,24 +14,27 @@ namespace {
 /// in. Shared by the raw walk and the bucket walk so the two cannot disagree about what an edge
 /// records -- an interval's width is the distance from the edge that entered it to the edge that
 /// left it, which is the pairing the pulse duration averages.
-void enter_side(MeasureLevel& acc, std::size_t e, double t) {
-  const std::size_t other = 1 - e;
-  if (acc.enters[e] == 0) acc.first_enter[e] = t;
-  acc.last_enter[e] = t;
-  ++acc.enters[e];
-  if (acc.open[other]) {
-    acc.width_sum[other] += t - acc.open_at[other];
-    ++acc.widths[other];
-    acc.open[other] = false;
-  }
-  acc.open_at[e] = t;
-  acc.open[e] = true;
-}
-
 // The hysteresis band and its rationale moved to `MeasureOptions::noise_pct`: it is a per-measurement
 // setting now, and a second copy of the number here would be a second thing to keep in step.
 constexpr double kPi = 3.14159265358979323846;
 
+/// The flat level's band, as a half-width in shares of the window's peak-to-peak. 5 % is *under*
+/// the overshoot a band-limited edge rings to -- Gibbs, about 9 % of the swing at the harmonic
+/// counts the mock's `square` uses -- so the ringing's excursion falls outside the densest band
+/// while a plateau's own ripple, a few percent, stays inside it. Measured on the mock's 30-harmonic
+/// square at 1.3 MS/s: the flat top reads 1.000000 with this band, 1.003573 at 3 %, 1.003495 at
+/// 10 % -- the wider bands reach the ringing again. A share and not an absolute width: the band is
+/// the same quantity `threshold_pct` and the hysteresis are measured in.
+constexpr double kFlatBandShare = 0.05;
+
+/// Which bin of a side is the level: the *outermost* one holding at least this share of the
+/// densest bin's buckets. One rule for both kinds of waveform. Where a plateau exists it is by
+/// far the densest band and the rule cannot reach past it. Where none exists -- a sine, a ramp --
+/// the signal dwells in every band it visits, the whole side qualifies, and the outermost is the
+/// honest answer: the level is then the top of what the window reaches, near the peak, rather
+/// than a bin of an arbitrary mid-range density that a shifted window would move.
+constexpr double kFlatTieShare = 0.5;
+
 }  // namespace
 
 void measure_set_level(MeasureLevel& acc, const MeasureStats& s, double pct, double noise_frac) {
@@ -116,14 +119,29 @@ void measure_scan(const MeasureChunk& chunk, MeasureStats& s, MeasureFilter& fil
   }
 }
 
-void measure_scan_buckets(const MeasureBucket* buckets, std::size_t count, MeasureStats& s) {
+void measure_scan_buckets(const MeasureBucket* buckets, std::size_t count, MeasureStats& s,
+                          bool flat_hist) {
   double sum = 0.0;
   std::size_t finite = 0;
+  // The *buckets'* own range, which is not the window's: the window's partial edge buckets are
+  // read raw and are not in this list. Only the non-empty buckets: an all-non-finite bucket is
+  // stored as an empty aggregate and its `lo`/`hi` say nothing.
+  double blo = 0.0;
+  double bhi = 0.0;
+  bool any = false;
   for (std::size_t b = 0; b < count; ++b) {
     const MeasureBucket& k = buckets[b];
     // A bucket of nothing (every sample non-finite) is stored as an empty aggregate, and the raw
     // walk skips exactly those samples -- so it contributes nothing here either.
     if (k.count == 0) continue;
+    if (!any) {
+      blo = k.lo;
+      bhi = k.hi;
+      any = true;
+    } else {
+      if (k.lo < blo) blo = k.lo;
+      if (k.hi > bhi) bhi = k.hi;
+    }
     sum += k.sum;
     finite += k.count;
     if (!s.valid) {
@@ -147,6 +165,27 @@ void measure_scan_buckets(const MeasureBucket* buckets, std::size_t count, Measu
   }
   s.sum += sum;
   s.count += finite;
+  if (!flat_hist || !any || !(bhi > blo)) return;
+  // One observation per bucket, at its midpoint, carrying that bucket's *exact* sum and finite
+  // count -- so the level the caller finally reports is a mean of real samples and not a bin
+  // centre. Weighting by the bucket (and not by its 64 samples) is what keeps the flat regions
+  // and the ringing on the same footing: the question is how much of the *waveform* dwells in a
+  // band, and a bucket is a span of it. A range that is degenerate (every bucket the same value)
+  // has no band to pick and leaves `folded` at 0, which is the caller's "no histogram".
+  s.flat.lo = blo;
+  s.flat.hi = bhi;
+  const double scale = static_cast<double>(MeasureFlatHist::kBins) / (bhi - blo);
+  for (std::size_t b = 0; b < count; ++b) {
+    const MeasureBucket& k = buckets[b];
+    if (k.count == 0) continue;
+    const double mid = 0.5 * (k.lo + k.hi);
+    std::size_t bin = mid <= blo ? 0u : static_cast<std::size_t>((mid - blo) * scale);
+    if (bin >= MeasureFlatHist::kBins) bin = MeasureFlatHist::kBins - 1;
+    s.flat.sum[bin] += k.sum;
+    s.flat.count[bin] += k.count;
+    ++s.flat.buckets[bin];
+    ++s.flat.folded;
+  }
 }
 
 void measure_accumulate(const MeasureChunk& chunk,
@@ -187,69 +226,96 @@ void measure_accumulate(const MeasureChunk& chunk,
   }
 }
 
-bool measure_accumulate_bucket(const MeasureBucket& k,
-                               const std::function<double(std::size_t)>& time_of,
-                               MeasureLevel& acc) {
-  if (k.count == 0) return true;
-  // A non-finite sample in the bucket would make the edge's position a guess: the raw walk takes
-  // the first *finite* sample of the new side, and an aggregate cannot say which that is.
-  if (k.count != k.span) return false;
-  // The *sums* need only the bare level: strictly on one side of it, so every sample decides the
-  // same bin and none is *at* it, which is what makes the fold exact rather than an approximation.
-  const bool above = k.lo > acc.level;
-  const bool below = k.hi < acc.level;
-  if (!above && !below) return false;
-  const std::size_t e = above ? 1u : 0u;
-  // The band is deliberately *not* folded into the test above. Tightening the whole condition to
-  // `level +/- h` refuses every bucket lying inside the band -- a tenth of the amplitude either side
-  // of the mid level is where a waveform moves fastest, so those are exactly the buckets a crossing
-  // passes through -- which hands the raw walk a share of the window rather than a bucket or two per
-  // crossing, and breaks the "`raw` stays at a fraction of a percent of `covered`" invariant.
-  // Instead: a bucket on one side of the level can always be *binned*, and only a *side change*
-  // whose position is inside the bucket is refused.
-  const double top = acc.level + acc.hysteresis;
-  const double bot = acc.level - acc.hysteresis;
-  // Does the bucket reach past the band at all? One wholly inside it decides no side, exactly as a
-  // raw sample inside it decides none, so the walk state is left alone.
-  const bool reaches = above ? (k.hi > top) : (k.lo < bot);
-  const bool change = reaches && acc.have_side && e != (acc.side ? 1u : 0u);
-  // A bucket that *enters* a side while straddling its own threshold holds the crossing somewhere
-  // inside itself, and only the raw walk can say where. One wholly past the threshold holds it at
-  // the bucket's first sample, exactly, which is where the raw walk would have found it.
-  const bool fully_outside = above ? (k.lo > top) : (k.hi < bot);
-  // Nothing may be folded before this point: a refusal hands the bucket to `measure_accumulate()`,
-  // which adds the same samples again. Sums added above the refusal double-counted every opened
-  // bucket, which read as `top` 0.614304 on a unit sine against the 2/pi it must be.
-  if (change && !fully_outside) return false;
-  acc.sum[e] += k.sum;
-  acc.count[e] += k.count;
-  if (change) enter_side(acc, e, time_of(k.offset));
-  if (reaches) {
-    acc.side = e != 0;
-    acc.have_side = true;
+
+MeasureFlatLevels measure_flat_levels(const MeasureStats& b, double pct) {
+  MeasureFlatLevels out;
+  const MeasureFlatHist& h = b.flat;
+  const double span = b.hi - b.lo;
+  if (h.folded == 0 || !(h.hi > h.lo) || !(span > 0.0)) return out;
+  // The split, sized exactly as `measure_set_level()` sizes the level the crossing types read, so
+  // "the top" and "the level a period is counted about" are placed by one rule.
+  const double level = b.lo + std::clamp(pct, 0.0, 1.0) * span;
+  const double width = (h.hi - h.lo) / static_cast<double>(MeasureFlatHist::kBins);
+  const double band = kFlatBandShare * span;
+  for (int upper = 1; upper >= 0; --upper) {
+    const auto in_side = [&](std::size_t i) {
+      const double centre = h.lo + (static_cast<double>(i) + 0.5) * width;
+      return (centre > level) == (upper != 0);
+    };
+    // One scan for the densest bin of this side, one for the outermost of the equally dense
+    // ones, one to sum the band about it: 192 iterations of an array of 64, per flat level.
+    std::size_t densest = 0;
+    for (std::size_t i = 0; i < MeasureFlatHist::kBins; ++i) {
+      if (in_side(i) && h.buckets[i] > densest) densest = h.buckets[i];
+    }
+    // A side of the split with no bucket in it has no level: `top` on a window that never reaches
+    // above the split reads `--`, which is exactly what it read before.
+    if (densest == 0) continue;
+    const double floor_buckets = kFlatTieShare * static_cast<double>(densest);
+    std::size_t anchor = 0;
+    bool have_anchor = false;
+    for (std::size_t i = 0; i < MeasureFlatHist::kBins; ++i) {
+      if (!in_side(i) || static_cast<double>(h.buckets[i]) < floor_buckets) continue;
+      // The upper side wants the *last* qualifier and the lower one the first, so a bottom-up scan
+      // is "always overwrite" for one and "only ever write once" for the other.
+      if (upper != 0 || !have_anchor) anchor = i;
+      have_anchor = true;
+    }
+    if (!have_anchor) continue;
+    const double centre = h.lo + (static_cast<double>(anchor) + 0.5) * width;
+    double sum = 0.0;
+    std::size_t count = 0;
+    for (std::size_t i = 0; i < MeasureFlatHist::kBins; ++i) {
+      const double offset = h.lo + (static_cast<double>(i) + 0.5) * width - centre;
+      if (offset < -band || offset > band) continue;
+      sum += h.sum[i];
+      count += h.count[i];
+    }
+    if (count == 0) continue;
+    if (upper != 0) {
+      out.top = sum / static_cast<double>(count);
+      out.top_ok = true;
+    } else {
+      out.bottom = sum / static_cast<double>(count);
+      out.bottom_ok = true;
+    }
   }
-  return true;
+  return out;
 }
 
-bool measure_level_pct(MeasureType type, const MeasureOptions& options, double& pct) {
+int measure_level_pcts(MeasureType type, const MeasureOptions& options, double pct[2]) {
+  const auto share = [](double v) { return std::clamp(v, 0.0, 100.0) / 100.0; };
   switch (type) {
     case MeasureType::Top:
     case MeasureType::Bottom:
-      pct = std::clamp(options.threshold_pct, 0.0, 100.0) / 100.0;
-      return true;
+    case MeasureType::Above:
+    case MeasureType::Below:
+      pct[0] = share(options.threshold_pct);
+      return 1;
+    case MeasureType::Between: {
+      // The band's two edges, clamped and *ordered*: the shares name a lower and an upper edge, so
+      // "between 80 % and 20 %" is the band between 20 % and 80 %. Normalizing rather than refusing
+      // is the honest reading of a band -- the set of samples does not depend on which edge the user
+      // typed first -- and the two accumulators the pair is answered from are keyed on these ordered
+      // values, so the same band is one walk however it was written.
+      const double a = share(options.threshold_pct);
+      const double b = share(options.threshold_pct2);
+      pct[0] = std::min(a, b);
+      pct[1] = std::max(a, b);
+      return 2;
+    }
     case MeasureType::PulseDuration:
     case MeasureType::Period:
     case MeasureType::Frequency:
       // The *mid* level, for all three. No option here on purpose: a period is the spacing of
       // one crossing per cycle, and a threshold near either extreme counts noise as crossings.
-      pct = 0.5;
-      return true;
+      pct[0] = 0.5;
+      return 1;
     default:
-      return false;
+      return 0;
   }
 }
 
-
 const char* measure_type_name(MeasureType type) {
   switch (type) {
     case MeasureType::Average: return "average";
@@ -262,11 +328,14 @@ const char* measure_type_name(MeasureType type) {
     case MeasureType::PulseDuration: return "pulse duration";
     case MeasureType::Period: return "period";
     case MeasureType::Frequency: return "frequency";
+    case MeasureType::Above: return "above";
+    case MeasureType::Below: return "below";
+    case MeasureType::Between: return "between";
   }
   return "?";
 }
 
-int measure_type_count() { return 10; }
+int measure_type_count() { return 13; }
 
 MeasureType measure_type_at(int index) {
   switch (index) {
@@ -279,15 +348,24 @@ MeasureType measure_type_at(int index) {
     case 6: return MeasureType::Amplitude;
     case 7: return MeasureType::PulseDuration;
     case 8: return MeasureType::Frequency;
-    default: return MeasureType::Period;
+    case 9: return MeasureType::Period;
+    // Appended rather than filed beside `Top`/`Bottom`, where they read best in the dropdown:
+    // `layout_store` writes *this* index into the session file, so renumbering would turn a saved
+    // `max` into an `above` on the next start -- silently, and only for users who had one.
+    case 10: return MeasureType::Above;
+    case 11: return MeasureType::Below;
+    default: return MeasureType::Between;
   }
 }
 
 bool measure_uses_threshold(MeasureType type) {
   return type == MeasureType::Top || type == MeasureType::Bottom ||
-         type == MeasureType::PulseDuration;
+         type == MeasureType::PulseDuration || type == MeasureType::Above ||
+         type == MeasureType::Below || type == MeasureType::Between;
 }
 
+bool measure_uses_band(MeasureType type) { return type == MeasureType::Between; }
+
 bool measure_uses_side(MeasureType type) { return type == MeasureType::PulseDuration; }
 
 bool measure_uses_noise(MeasureType type) {
@@ -297,8 +375,8 @@ bool measure_uses_noise(MeasureType type) {
 
 bool measure_can_show_on_plot(MeasureType) { return true; }
 
-MeasureResult compute_measure(const MeasureStats& b, const MeasureLevel* level, MeasureType type,
-                              const MeasureOptions& options) {
+MeasureResult compute_measure(const MeasureStats& b, const MeasureLevel* const levels[2],
+                              MeasureType type, const MeasureOptions& options) {
   MeasureResult out;
   if (!b.valid) return out;
 
@@ -323,11 +401,11 @@ MeasureResult compute_measure(const MeasureStats& b, const MeasureLevel* level,
       out.valid = true;
       return out;
     }
-    case MeasureType::PeakToPeak:
-    case MeasureType::Amplitude: {
-      // Both come straight out of the window's own extremes, which every type already needs:
-      // the two rulers are the same pair, and the numbers differ by a factor of two.
-      out.primary = type == MeasureType::PeakToPeak ? b.hi - b.lo : 0.5 * (b.hi - b.lo);
+    case MeasureType::PeakToPeak: {
+      // Straight out of the window's own extremes, which every type already needs: this one *is*
+      // the extremes, ripple and overshoot included -- that is the difference between it and
+      // `Amplitude`, which reads the two levels the signal dwells at instead.
+      out.primary = b.hi - b.lo;
       // A ruler at each extreme: the *span* is the measurement, and two levels are how a
       // plot states a span without a band between them.
       out.marks.push_back({true, b.lo});
@@ -335,15 +413,88 @@ MeasureResult compute_measure(const MeasureStats& b, const MeasureLevel* level,
       out.valid = true;
       return out;
     }
+    case MeasureType::Amplitude: {
+      // The delta between the two flat levels, so a ringing edge's overshoot is not part of it.
+      // The split is the mid level, fixed rather than an option -- the dialog offers no threshold
+      // for this type -- and the reading is insensitive to it anyway: the band a level is read from
+      // is a *value* band, so any split between the two plateaus picks the same two.
+      const MeasureFlatLevels flat = measure_flat_levels(b, 0.5);
+      if (flat.top_ok && flat.bottom_ok) {
+        out.primary = flat.top - flat.bottom;
+        out.marks.push_back({true, flat.top});
+        out.marks.push_back({true, flat.bottom});
+        out.valid = true;
+        return out;
+      }
+      // No density estimate to separate a plateau from its ringing: a window shorter than a
+      // bucket, or an HF-rejected walk, which cannot use the pyramid at all. The delta then
+      // degenerates to the window's own peak to peak -- the same number when there is nothing to
+      // exclude, and the only honest one when the ripple cannot be told from the level.
+      out.primary = b.hi - b.lo;
+      out.marks.push_back({true, b.lo});
+      out.marks.push_back({true, b.hi});
+      out.valid = true;
+      return out;
+    }
     case MeasureType::Top:
     case MeasureType::Bottom: {
-      // The mean of one side of the level, straight out of the second pass' running sums. A flat
-      // window has no range at all, so every sample lands on the "below" side -- which is why
-      // `top` on a signal that never moves reads `--` rather than that one value.
-      if (level == nullptr) return out;
-      const std::size_t s = type == MeasureType::Top ? 1 : 0;
-      if (level->count[s] == 0) return out;
-      out.primary = level->sum[s] / static_cast<double>(level->count[s]);
+      // The flat level of one side of the split: the densest band there, whose samples' exact mean
+      // is the value. The band is a *value* band, so the reading does not follow the window's
+      // alignment, and it excludes both a plateau's ripple and an edge's overshoot -- which is the
+      // whole point, because those are exactly what a mean over a side reports instead.
+      double pct[2] = {0.0, 0.0};
+      if (measure_level_pcts(type, options, pct) == 0) return out;
+      const bool want_top = type == MeasureType::Top;
+      const MeasureFlatLevels flat = measure_flat_levels(b, pct[0]);
+      if (want_top ? flat.top_ok : flat.bottom_ok) {
+        out.primary = want_top ? flat.top : flat.bottom;
+        out.marks.push_back({true, out.primary});
+        out.valid = true;
+        return out;
+      }
+      // No histogram: the mean of one side of the level, straight out of the second pass' running
+      // sums. A window the pyramid cannot summarize is one bucket or two of a zoomed-in view, or
+      // an HF-rejected walk, and on those the split's own means are the honest reading -- and they
+      // are what `Above`/`Below` report on *every* window.
+      const MeasureLevel* lv = levels != nullptr ? levels[0] : nullptr;
+      const std::size_t s = want_top ? 1 : 0;
+      if (lv == nullptr || lv->count[s] == 0) return out;
+      out.primary = lv->sum[s] / static_cast<double>(lv->count[s]);
+      out.marks.push_back({true, out.primary});
+      out.valid = true;
+      return out;
+    }
+    case MeasureType::Above:
+    case MeasureType::Below: {
+      // The plain mean of the samples on one side of the share -- what `Top`/`Bottom` reported
+      // before they became flat levels, and a different question from them: a mean over a side
+      // carries the ripple and the edge's overshoot (0.986496 on the rippled square where the
+      // plateau is 1), which is exactly why the flat-level types exist beside these.
+      const MeasureLevel* lv = levels != nullptr ? levels[0] : nullptr;
+      const std::size_t s = type == MeasureType::Above ? 1 : 0;
+      if (lv == nullptr || lv->count[s] == 0) return out;
+      out.primary = lv->sum[s] / static_cast<double>(lv->count[s]);
+      out.marks.push_back({true, out.primary});
+      out.valid = true;
+      return out;
+    }
+    case MeasureType::Between: {
+      // The band's interior: what lies above the lower edge and *not* above the upper one. Both
+      // accumulators split the same samples the same way -- pass two walks one bucket list and one
+      // filter for the whole window -- so the band is the *difference* of the two upper sides, and
+      // it is exact rather than approximate. It needs no third walk of its own, and the bucket
+      // fast path serves it unchanged: a bucket wholly inside the band is strictly above the lower
+      // level and strictly below the upper, so both accumulators fold it whole.
+      const MeasureLevel* lower = levels != nullptr ? levels[0] : nullptr;
+      const MeasureLevel* upper = levels != nullptr ? levels[1] : nullptr;
+      if (lower == nullptr || upper == nullptr) return out;
+      // Equal counts mean an empty interior: nothing lies in the band, so there is nothing to
+      // average -- the pane reads `--`, as it does for any other type with no samples on the side
+      // it was asked about. `lower` may not count *fewer*, which would say the two accumulators
+      // saw different samples.
+      if (lower->count[1] <= upper->count[1]) return out;
+      out.primary = (lower->sum[1] - upper->sum[1]) /
+                    static_cast<double>(lower->count[1] - upper->count[1]);
       out.marks.push_back({true, out.primary});
       out.valid = true;
       return out;
@@ -351,18 +502,19 @@ MeasureResult compute_measure(const MeasureStats& b, const MeasureLevel* level,
     case MeasureType::PulseDuration:
     case MeasureType::Period:
     case MeasureType::Frequency: {
-      if (level == nullptr) return out;
+      if (levels == nullptr || levels[0] == nullptr) return out;
+      const MeasureLevel& level = *levels[0];
       // The pulse is one side of the mid level: its widths run from the edge that enters it to
       // the edge that leaves it, and a period is the spacing of the edges that *enter* it -- one
       // per cycle, whatever else the waveform does in between.
       const std::size_t s = options.above ? 1 : 0;
-      const double enter_span = level->last_enter[s] - level->first_enter[s];
-      const double enter_period = level->enters[s] >= 2
-                                      ? enter_span / static_cast<double>(level->enters[s] - 1)
+      const double enter_span = level.last_enter[s] - level.first_enter[s];
+      const double enter_period = level.enters[s] >= 2
+                                      ? enter_span / static_cast<double>(level.enters[s] - 1)
                                       : 0.0;
       if (type == MeasureType::PulseDuration) {
-        if (level->widths[s] == 0) return out;
-        out.primary = level->width_sum[s] / static_cast<double>(level->widths[s]);
+        if (level.widths[s] == 0) return out;
+        out.primary = level.width_sum[s] / static_cast<double>(level.widths[s]);
         // Duty as width/period, not as pulse-time over the window: a window that starts or
         // ends mid-pulse holds partial cycles, and counting only the complete ones against
         // the whole span would report a duty that depends on where the window happened to
@@ -370,15 +522,15 @@ MeasureResult compute_measure(const MeasureStats& b, const MeasureLevel* level,
         // them -- a window holding one pulse reports the width alone.
         out.secondary = enter_period > 0.0 ? out.primary / enter_period : 0.0;
         out.has_secondary = enter_period > 0.0;
-        out.marks.push_back({false, level->first_enter[s]});
-        out.marks.push_back({false, level->first_enter[s] + out.primary});
+        out.marks.push_back({false, level.first_enter[s]});
+        out.marks.push_back({false, level.first_enter[s] + out.primary});
         out.valid = true;
         return out;
       }
       if (!(enter_period > 0.0)) return out;
       out.primary = type == MeasureType::Period ? enter_period : 1.0 / enter_period;
-      out.marks.push_back({false, level->first_enter[s]});
-      out.marks.push_back({false, level->first_enter[s] + enter_period});
+      out.marks.push_back({false, level.first_enter[s]});
+      out.marks.push_back({false, level.first_enter[s] + enter_period});
       out.valid = true;
       return out;
     }
@@ -386,5 +538,4 @@ MeasureResult compute_measure(const MeasureStats& b, const MeasureLevel* level,
   return out;
 }
 
-
 }  // namespace udpscope

src/measure.hpp

@@ -17,28 +17,58 @@ enum class MeasureType {
   Min,            ///< the smallest visible value
   Max,            ///< the largest visible value
   /// The largest swing in the window: `max - min`, the two extremes the eye would measure
-  /// with a ruler across the waveform.
+  /// with a ruler across the waveform -- ripple and overshoot included, which is what makes it
+  /// the *extremes* and not a level.
   PeakToPeak,
-  /// Half the peak-to-peak swing, `(max - min) / 2` -- the amplitude of a symmetric waveform
-  /// about its own mean, which is the figure a datasheet quotes and a signal generator is set
-  /// to. Deliberately not `max(|value|)`: that is a *distance from zero*, which for a signal
-  /// riding on an offset is a different and less useful number.
+  /// The delta between the two **flat** levels, `top - bottom` (a bench scope's `Vamplitude`,
+  /// which is `Vtop - Vbase`). Deliberately *not* the peak-to-peak swing: a band-limited edge
+  /// overshoots and rings, so the extremes of a nominal 2 V square read about 2.36 V, while the
+  /// levels the signal actually dwells at are ±1 and their delta exactly 2. Where the window
+  /// has no density estimate to separate a plateau from its ripple (shorter than one bucket, or
+  /// an HF-rejected walk) it degenerates to the window's own peak to peak, which is the same
+  /// number on a waveform with nothing to exclude. Never `max(|value|)`: that is a *distance
+  /// from zero*, which for a signal riding on an offset is a different and less useful number.
   Amplitude,
-  Top,            ///< the signal's high level (the mean of the samples above the threshold)
-  Bottom,         ///< the signal's low level (the mean of the samples below it)
+  /// The signal's high level: the densest band of the window's upper side, whose samples' exact
+  /// mean is the value -- the *flat top*, so a plateau's ripple and an edge's overshoot neither
+  /// define it nor enter it.
+  Top,
+  /// The signal's low level, the same way from the window's lower side.
+  Bottom,
   PulseDuration,  ///< how long the signal spends on one side of the threshold
   Period,         ///< the time between two successive crossings of the threshold
   Frequency,      ///< 1 / period
+  /// The mean of the samples **above** `threshold_pct` -- the split's own upper mean, which is
+  /// what `Top` reported before a flat level replaced it. `Top`/`Bottom` are the level the signal
+  /// *dwells at* (a density question, so a ringing edge does not drag them); these two are the
+  /// plain mean of the samples on one side of the share, ripple and overshoot included, which is
+  /// a *different* question about the same split and the reason the two coexist: on a unit sine
+  /// this reads `0.636620` (2/pi) where `Top` reads `0.957988`, and on the mock's band-limited
+  /// square `0.986496` where its plateau is 1.
+  Above,
+  /// The same from the split's lower side.
+  Below,
+  /// The mean of the samples **between** `threshold_pct` and `threshold_pct2`: the band's
+  /// interior, which neither of the two means above can answer (one of them gives the two sides
+  /// and the other the whole window, because the band's two edges are not one split).
+  Between,
 };
 
 /// Type-specific behaviour. Every field is meaningful only for the types named below; the
 /// others ignore it (an option that does nothing for a type is left out of the dialog
 /// rather than stored and ignored).
 struct MeasureOptions {
-  /// `Top`/`Bottom`/`PulseDuration`/`Period`/`Frequency`: where the split is, as a share of
+  /// `Top`/`Bottom`/`PulseDuration`/`Above`/`Below`/`Between`: where the split is, as a share of
   /// the window's own min..max. The middle by default, which is what a symmetric waveform
-  /// wants; a 3.3 V logic signal with ringing wants it nearer the top.
+  /// wants; a 3.3 V logic signal with ringing wants it nearer the top. For `Above`/`Below` it is
+  /// the level the mean is taken on one side of; for `Between` it is the band's *lower* edge.
   double threshold_pct = 50.0;
+  /// `Between`: the band's other edge, the same unit. The two are read through
+  /// `measure_level_pcts()`, which clamps both and puts the pair in order, so the band between
+  /// 80 % and 20 % is the band between 20 % and 80 % -- the shares name two *edges* and the order
+  /// they were typed in carries no meaning, which is why a reversed pair is normalized rather
+  /// than refused.
+  double threshold_pct2 = 75.0;
   /// `PulseDuration`: which side of the threshold is "the pulse". `Period`/`Frequency`
   /// use it as the edge direction, so one cycle is counted once.
   bool above = true;
@@ -92,6 +122,35 @@ struct MeasureResult {
   bool valid = false;
 };
 
+/// The density estimate behind `Top`/`Bottom`/`Amplitude`: one bin per band of the window's
+/// value range, over the whole LOD buckets pass one walked.
+///
+/// A flat level is a *density* question, not an extreme one: on a band-limited square the
+/// plateau holds most of the samples while the edge's ringing holds a few percent, so the
+/// densest band is the level the signal dwells at and the ringing is what a mean over a side
+/// reports instead. One bucket is one observation at its midpoint -- a bucket is 64 samples
+/// held as one aggregate, so counting its samples would weight a flat region by nothing at all
+/// and a ringing one by 64 -- and each bin also carries the exact sum and count of the samples
+/// its buckets hold, which is what makes the reported level an exact mean rather than a bin
+/// centre. The bucket list is the one pass one already fetches; no pass reads raw samples for
+/// this, which is the whole reason it is built from buckets and not from a sample histogram
+/// (that would be a second O(window) walk).
+struct MeasureFlatHist {
+  /// Bins across the buckets' own range. The band the level is read from is picked at this
+  /// resolution and is a share of the *window's* peak-to-peak, so the bin count only sets how
+  /// finely the densest band can be located.
+  static constexpr std::size_t kBins = 64;
+  double lo = 0.0;  ///< the bin range: the whole buckets' own smallest `lo`..
+  double hi = 0.0;  ///< ..and largest `hi`. Empty when nothing was folded.
+  double sum[kBins] = {};
+  std::size_t count[kBins] = {};
+  std::size_t buckets[kBins] = {};
+  /// Whole buckets folded in: 0 means this window has no histogram at all (a window shorter
+  /// than a bucket, or an HF-rejected walk, which cannot use the pyramid), and the flat-level
+  /// types then fall back to their split-relative readings.
+  std::size_t folded = 0;
+};
+
 /// The window's own extremes, which every threshold-relative type scales from and which
 /// several types report directly. Public so a caller holding *several* measurements on one
 /// signal can pay for the scan once: it is O(visible samples) and a live view at 1 MS/s makes
@@ -119,6 +178,10 @@ struct MeasureStats {
   /// `compute_measure()` reads these, so a caller that skips the resolve reports t = 0.
   double at_lo = 0.0;
   double at_hi = 0.0;
+  /// The flat levels' density estimate, folded from the same whole buckets pass one walked.
+  /// The *values* are resolved by `measure_flat_levels()`, which needs the split and the
+  /// window's span and so cannot be done until the walk is over.
+  MeasureFlatHist flat;
   bool valid = false;
 };
 
@@ -195,7 +258,14 @@ void measure_scan(const MeasureChunk& chunk, MeasureStats& stats, MeasureFilter&
 /// Pass one from whole buckets: the same figures, exactly, for 1/64 of the reads. The extreme's
 /// position comes out as a *bucket* (`lo_search`/`hi_search` non-zero), which one raw
 /// `measure_scan()` of that bucket then pins. Interleave with `measure_scan()` in window order.
-void measure_scan_buckets(const MeasureBucket* buckets, std::size_t count, MeasureStats& stats);
+///
+/// `flat_hist` folds the same list into `stats.flat` for the flat-level types, in a second tight
+/// loop over the array (the bin range is the buckets' own, which the first loop is what
+/// discovers). That loop is O(buckets) and reads no sample, so the `measure cost:` line's `raw`
+/// is unchanged by it -- the cost is buckets, which is the budget the pane is on. It is the
+/// caller's because only the caller knows whether any measurement reads a flat level.
+void measure_scan_buckets(const MeasureBucket* buckets, std::size_t count, MeasureStats& stats,
+                          bool flat_hist);
 
 /// Everything the threshold-relative types need from a second walk, at one level: the sum and
 /// count of the samples on either side of it, and its crossings reduced to running figures -- the
@@ -215,12 +285,19 @@ struct MeasureLevel {
   /// `period=0.025622 freq=39.029` for a true 0.2 s / 5 Hz. With the band, `period=0.200188`.
   ///
   /// It moves the *edge decision* only. The `sum`/`count` split below stays at the bare `level`,
-  /// because that is what `Top`/`Bottom` are -- the mean of the samples above/below the threshold --
-  /// and a band there would change a documented exact reading (`top` on a unit sine is 2/pi).
-  /// `measure_set_level()` is what sizes it; zero reduces the walk exactly to a single level.
+  /// so a band can never change it -- the split is the split, and a sample's side of it is a
+  /// fact rather than a threshold decision. `measure_set_level()` is what sizes it; zero reduces
+  /// the walk exactly to a single level.
   double hysteresis = 0.0;
-  /// Index 0 is the side below the level (a sample exactly *at* it counts here, which is what
-  /// `bottom` has always reported), index 1 the side above it.
+  /// The samples either side of `level`, exactly: the reading of `Above`/`Below` is one of these
+  /// two means, `Between`'s is the difference of two *levels'* upper sides, and `Top`/`Bottom` fall
+  /// back to them on a window with no bucket histogram to read a flat level from (shorter than one
+  /// bucket, or an HF-rejected walk). They are folded on every window -- pass two walks it for the
+  /// crossing types anyway -- but a window that has a histogram is read from that instead, because
+  /// a mean over a side reports the ripple and the overshoot rather than the level the signal
+  /// dwells at.
+  /// Index 0 is the side below the level (a sample exactly *at* it counts here), index 1 the
+  /// side above it.
   double sum[2] = {0.0, 0.0};
   std::size_t count[2] = {0, 0};
   double first_enter[2] = {0.0, 0.0};
@@ -272,16 +349,102 @@ bool measure_accumulate_bucket(const MeasureBucket& bucket,
                                const std::function<double(std::size_t)>& time_of,
                                MeasureLevel& level);
 
-/// The level a type reads, as a share of the window's own min..max, or false when it reads none
-/// (the pure statistics, answered from `MeasureStats` alone). `Top`/`Bottom` read the
-/// measurement's own threshold; the crossing types read the mid level, deliberately -- see
-/// `measure_uses_threshold()`.
-bool measure_level_pct(MeasureType type, const MeasureOptions& options, double& pct);
+inline void enter_side(MeasureLevel& acc, std::size_t e, double t) {
+  const std::size_t other = 1 - e;
+  if (acc.enters[e] == 0) acc.first_enter[e] = t;
+  acc.last_enter[e] = t;
+  ++acc.enters[e];
+  if (acc.open[other]) {
+    acc.width_sum[other] += t - acc.open_at[other];
+    ++acc.widths[other];
+    acc.open[other] = false;
+  }
+  acc.open_at[e] = t;
+  acc.open[e] = true;
+}
 
-/// The engine: one measurement's answer, O(1), from the two passes' results. `level` is the
-/// accumulator for `measure_level_pct(type, options)` and may be null for the types that read
-/// none. The function reads nothing else, which is what keeps the answer independent of the plot.
-MeasureResult compute_measure(const MeasureStats& stats, const MeasureLevel* level,
+inline bool measure_accumulate_bucket(const MeasureBucket& k,
+                               const std::function<double(std::size_t)>& time_of,
+                               MeasureLevel& acc) {
+  if (k.count == 0) return true;
+  // A non-finite sample in the bucket would make the edge's position a guess: the raw walk takes
+  // the first *finite* sample of the new side, and an aggregate cannot say which that is.
+  if (k.count != k.span) return false;
+  // The *sums* need only the bare level: strictly on one side of it, so every sample decides the
+  // same bin and none is *at* it, which is what makes the fold exact rather than an approximation.
+  const bool above = k.lo > acc.level;
+  const bool below = k.hi < acc.level;
+  if (!above && !below) return false;
+  const std::size_t e = above ? 1u : 0u;
+  // The band is deliberately *not* folded into the test above. Tightening the whole condition to
+  // `level +/- h` refuses every bucket lying inside the band -- a tenth of the amplitude either side
+  // of the mid level is where a waveform moves fastest, so those are exactly the buckets a crossing
+  // passes through -- which hands the raw walk a share of the window rather than a bucket or two per
+  // crossing, and breaks the "`raw` stays at a fraction of a percent of `covered`" invariant.
+  // Instead: a bucket on one side of the level can always be *binned*, and only a *side change*
+  // whose position is inside the bucket is refused.
+  const double top = acc.level + acc.hysteresis;
+  const double bot = acc.level - acc.hysteresis;
+  // Does the bucket reach past the band at all? One wholly inside it decides no side, exactly as a
+  // raw sample inside it decides none, so the walk state is left alone.
+  const bool reaches = above ? (k.hi > top) : (k.lo < bot);
+  const bool change = reaches && acc.have_side && e != (acc.side ? 1u : 0u);
+  // A bucket that *enters* a side while straddling its own threshold holds the crossing somewhere
+  // inside itself, and only the raw walk can say where. One wholly past the threshold holds it at
+  // the bucket's first sample, exactly, which is where the raw walk would have found it.
+  const bool fully_outside = above ? (k.lo > top) : (k.hi < bot);
+  // Nothing may be folded before this point: a refusal hands the bucket to `measure_accumulate()`,
+  // which adds the same samples again. Sums added above the refusal double-counted every opened
+  // bucket -- which read as `top` 0.614304 on a unit sine against the 2/pi a mean over a half then
+  // gave, and which is now the sums `Top`/`Bottom` fall back to on a window with no histogram, so
+  // a wrong one is a wrong answer waiting for that window.
+  if (change && !fully_outside) return false;
+  acc.sum[e] += k.sum;
+  acc.count[e] += k.count;
+  if (change) enter_side(acc, e, time_of(k.offset));
+  if (reaches) {
+    acc.side = e != 0;
+    acc.have_side = true;
+  }
+  return true;
+}
+
+/// The levels a type reads, as shares of the window's own min..max, **lower first**, or 0 when it
+/// reads none (the pure statistics, answered from `MeasureStats` alone). `pct` must hold two: a
+/// level type fills `pct[0]` and answers 1, `Between` fills both and answers 2.
+///
+/// `Top`/`Bottom`/`Above`/`Below` read the measurement's own threshold; the crossing types read the
+/// mid level, deliberately -- see `measure_uses_threshold()`. `Amplitude` reads no level either: its
+/// value is the delta between the two flat levels, which the histogram answers, and the split's two
+/// means are only a fallback it takes from the window's own extremes -- see `compute_measure()`.
+///
+/// This is the one place `Between`'s pair is clamped and ordered, so the pane's dedup key, the
+/// engine's two accumulators and the dialog all describe the same band whatever was typed.
+int measure_level_pcts(MeasureType type, const MeasureOptions& options, double pct[2]);
+
+/// The window's two flat levels, from the bucket histogram in `stats.flat`. `top` is the densest
+/// band of the bins *above* `lo + pct * (hi - lo)`, `bottom` the same below it -- for a
+/// crossing type's mid level that is the two plateaus of a pulse train, and for `Top`/`Bottom`'s
+/// own threshold it is "which side is the level I want". Each side is false when it holds no
+/// bucket, and both are false when the window has no histogram at all.
+///
+/// Two things this does not do. It does not read a sample: every figure comes from buckets pass
+/// one already fetched. And it does not read the window raw, which is why the answer is
+/// independent of how the window happens to be aligned -- the band is a *value* band, so the
+/// level it reports does not move when the window does.
+struct MeasureFlatLevels {
+  double top = 0.0;
+  bool top_ok = false;
+  double bottom = 0.0;
+  bool bottom_ok = false;
+};
+MeasureFlatLevels measure_flat_levels(const MeasureStats& stats, double pct);
+
+/// The engine: one measurement's answer, O(1), from the two passes' results. `levels` is the
+/// accumulators `measure_level_pcts(type, options)` asked for, in the same order -- `nullptr` for
+/// the types that read none, and either entry may be null when the caller could not resolve it.
+/// The function reads nothing else, which is what keeps the answer independent of the plot.
+MeasureResult compute_measure(const MeasureStats& stats, const MeasureLevel* const levels[2],
                               MeasureType type, const MeasureOptions& options);
 
 /// A measurement type's name, as the pane's row and the dialog's dropdown spell it.
@@ -294,12 +457,16 @@ MeasureType measure_type_at(int index);
 /// spacing of the crossings of the *mid* level, one rising edge per cycle, and offering a
 /// threshold there only invites a setting that makes the count wrong.
 bool measure_uses_threshold(MeasureType type);
+/// Whether a type reads a *pair* of shares, so the dialog shows its second share only then: the
+/// two edges of a band are one measurement's two parameters, and one field of the two is a
+/// measurement of a different band than the user asked for.
+bool measure_uses_band(MeasureType type);
 /// Whether a type uses the `above` side (only `PulseDuration`, where it says which half of
 /// the waveform is the pulse).
 bool measure_uses_side(MeasureType type);
 /// Whether a type reads the hysteresis band, so the dialog can show the field only then. The band moves
-/// the *edge* decision and nothing else, so it is exactly the crossing types: `Top`/`Bottom` split their
-/// sums at the bare level and read the same answer at any band.
+/// the *edge* decision and nothing else, so it is exactly the crossing types: `Top`/`Bottom` read a flat
+/// level out of the bucket histogram, which no band touches.
 bool measure_uses_noise(MeasureType type);
 /// Whether a type draws its result on the plot when asked.
 bool measure_can_show_on_plot(MeasureType type);

src/model.cpp

@@ -3,7 +3,7 @@
 
 #include "model.hpp"
 
-#include <udps_client.h>
+#include "status_text.hpp"  // `format_samples()` / `format_bytes()`, for the one line a clipped plan prints
 
 #include <algorithm>
 #include <chrono>
@@ -42,12 +42,24 @@ constexpr std::uint64_t kMathCostSample = 1024;
 
 }  // namespace
 
-Partition plan_partition(const std::vector<double>& channel_dt, double buffer_bytes,
-                         double target_span_s, bool with_abs_time) {
+u64 buffer_ticks(u64 requested_samples) {
+  // 2^40 slots is already 8 TiB of clock alone: a request past it is nonsense and the cap keeps
+  // `bytes_for()` far from overflowing.
+  constexpr u64 kMaxTicks = u64(1) << 40;
+  return std::min(pow2_floor(std::max<u64>(requested_samples, 128)), kMaxTicks);
+}
+
+u64 planned_bytes(u64 ticks, std::size_t channels, bool with_abs_time) {
+  return ticks * sizeof(f64) * (with_abs_time ? 2u : 1u) + ticks * sizeof(f32) * channels;
+}
+
+Partition plan_partition(const std::vector<double>& channel_dt, u64 samples_per_signal,
+                         u64 max_bytes, double target_span_s, bool with_abs_time) {
   Partition p;
   const std::size_t n = channel_dt.size();
   p.stride.assign(n, 1);
   p.value_capacity.assign(n, 0);
+  p.requested_samples = samples_per_signal;
   if (n == 0) return p;
 
   // The fastest channel drives the shared time base: every other channel is
@@ -71,25 +83,13 @@ Partition plan_partition(const std::vector<double>& channel_dt, double buffer_by
 
   p.abs_time = with_abs_time;
 
-  const u64 budget_bytes = static_cast<u64>(std::max(1.0, buffer_bytes));
-  // Weighted in *bytes*, not in slots: the shared clock is f64 and the values are f32
-  // (see `BufferStore::time()`), so a time slot costs twice a value sample and the two
-  // slices are not interchangeable. Counting both as one f32 is what would make
-  // `--buffer-mb` quietly understate the time ring by its own size.
-  double weight = static_cast<double>(sizeof(f64)) * (with_abs_time ? 2.0 : 1.0);  // the time slice(s)
-  for (u64 s : p.stride) weight += static_cast<double>(sizeof(f32)) / static_cast<double>(s);
-
-  const u64 slots = static_cast<u64>(static_cast<double>(budget_bytes) / weight);
-  u64 time_capacity = pow2_floor(std::max<u64>(slots, 128));
-  if (time_capacity == 0) {
-    throw std::runtime_error("buffer too small for one time-base sample per channel");
-  }
-
-  // The target span sets a floor, not a ceiling: the rest of the budget buys a
-  // longer ring, which is strictly more history to scroll back through. Growth
-  // stops before the total would exceed the budget. A channel's slots are rounded
-  // *up* on the power of two `RingBuffer` will round them to anyway, so every
-  // channel covers at least the time ring's span.
+  // The ring is a power of two, so the user's count is a ceiling and the plan takes the largest
+  // power of two under it. The budget is in *samples* now: it is the memory limit, not the request,
+  // that is in bytes -- and a time slot (f64) and a value sample (f32) are not the same size, which
+  // is why the limit below is weighed with `bytes_for()` and not as a count of slots.
+  //
+  // A channel's slots are rounded *down* on the power of two `RingBuffer` will round them to
+  // anyway, so every channel covers at most the time ring's span.
   // Floor, not ceiling: a channel's window must not be *longer* than the time ring
   // it reads its stamps from. Rounding up (with a stride that is not a power of two)
   // gave a channel more samples than the shared timeline covers, and the oldest of
@@ -105,19 +105,24 @@ Partition plan_partition(const std::vector<double>& channel_dt, double buffer_by
     for (u64 s : p.stride) total += capacity_for(ticks, s) * sizeof(f32);
     return total;
   };
-  // `bytes_for` bounds the doubling on its own: it is at least `2 * ticks * sizeof(f64)`,
-  // so a pass means `2 * ticks` is well inside the budget and cannot overflow.
-  while (bytes_for(time_capacity * 2) <= budget_bytes) {
-    time_capacity *= 2;
+  u64 time_capacity = buffer_ticks(samples_per_signal);
+  const u64 wanted_ticks = time_capacity;
+  // The memory limit halves the request until the rings fit, never the other way: a bigger plan than
+  // asked for is not "up to".
+  while (time_capacity > 128 && bytes_for(time_capacity) > max_bytes) time_capacity /= 2;
+  if (bytes_for(time_capacity) > max_bytes) {
+    throw std::runtime_error("memory limit too small for the sample rings of " +
+                             std::to_string(n) + " channels");
   }
+  p.memory_limited = time_capacity < wanted_ticks;
   p.time_capacity = time_capacity;
   for (std::size_t i = 0; i < n; ++i) {
     p.value_capacity[i] = capacity_for(p.time_capacity, p.stride[i]);
   }
 
-  // Only now, with the ring as long as the budget can buy, decimate the shared clock
+  // Only now, with the ring as long as the request and the memory limit allow, decimate the shared clock
   // enough for the requested window to fit in it: deciding this earlier would over-
-  // decimate by whatever factor the growth loop was about to add. A power of two keeps
+  // decimate by whatever the ring's final length would have made unnecessary. A power of two keeps
   // the ring capacities (themselves powers of two) in step and lets the producer's group
   // test be a mask (`Acquisition::acc_mask_`) rather than a modulo -- a modulo on a stride
   // this function chose at runtime is a real 64-bit division, which the test *was* paying
@@ -180,6 +185,7 @@ void BufferStore::acquire_all() {
 // --- ScopeModel -------------------------------------------------------------
 
 ScopeModel::ScopeModel(const Config& cfg) : cfg_(cfg) {
+  memory_limit_bytes_.store(cfg.memory_limit_mb * 1024u * 1024u, std::memory_order_relaxed);
   trigger_.holdoff_s = cfg.trigger_holdoff_s;
 }
 
@@ -226,6 +232,13 @@ void ScopeModel::set_signals(std::vector<SignalInfo> signals) {
   signals.erase(std::remove_if(signals.begin(), signals.end(),
                                [](const SignalInfo& s) { return s.math; }),
                 signals.end());
+  // The renames come off the stream's own units first, so that an identical CONFIG still compares
+  // equal against `signals_` (which holds the renamed ones) and a reconnect keeps its history.
+  declared_unit_.clear();
+  for (SignalInfo& s : signals) {
+    declared_unit_[s.name] = s.unit;
+    if (const auto it = unit_override_.find(s.name); it != unit_override_.end()) s.unit = it->second;
+  }
   if (!signals_.empty() && same_stream_signals(signals, signals_)) {
     // A reconnect's identical CONFIG: the honest recovery is *nothing* -- the ring keeps
     // its history, the trigger keeps its state and its held event, and the outage shows
@@ -449,6 +462,14 @@ void ScopeModel::recompute_math_locked(const std::vector<bool>& affected) {
   const std::size_t slots = static_cast<std::size_t>(store.time().size());
   if (slots == 0) return;
 
+  // The refill replays the inputs' *retained* window, which starts at this absolute index and not at
+  // zero, so an emptied derived ring has to resume its count there: `clear()` would renumber it from 0
+  // and leave its `produced()` short by `base` for a whole ring's worth of fresh data. `live_window_locked()`
+  // clamps the window against every channel's `produced()`, so that one lagging channel collapses the
+  // live view, every pause view and every trigger capture to nothing -- the "acquisition freezes after a
+  // math edit" defect, invisible until the ring has wrapped once (`base == 0` before that).
+  const std::size_t base = static_cast<std::size_t>(store.time().base());
+
   std::vector<bool> derived(channels_.size(), false);
   for (std::size_t m = 0; m < math_.size(); ++m) {
     const int channel = m < math_channel_.size() ? math_channel_[m] : -1;
@@ -456,14 +477,18 @@ void ScopeModel::recompute_math_locked(const std::vector<bool>& affected) {
     derived[static_cast<std::size_t>(channel)] = true;
     // Only the affected channels start again. The rest keep their samples *and* their runtimes: their graphs
     // are untouched, so the state they hold is the answer to the inputs they have always had.
-    if (affected[m]) store.values(static_cast<std::size_t>(channel)).clear();
+    if (!affected[m]) continue;
+    store.values(static_cast<std::size_t>(channel)).clear_to(base);
+    // And the published window with them: this is a rewrite in place, so `produced()` lands back where it
+    // started and the incremental `acquire()` would publish nothing at all -- leaving the pyramid, which is
+    // what the renderer and every measurement read, describing the samples the edit just replaced.
+    store.channel(static_cast<std::size_t>(channel)).republish_from(base);
   }
 
   // One bulk copy per channel per chunk, through the ring's own reader. A derived channel is fed a zero:
   // `math_apply_locked()` overwrites its value as it walks the list in order, and reading its half-rebuilt
   // ring here would read out of range.
   constexpr std::size_t kChunk = 1u << 14;
-  const std::size_t base = static_cast<std::size_t>(store.time().base());
   std::vector<std::vector<f32>> inputs(channels_.size());
   for (std::size_t c = 0; c < channels_.size(); ++c) {
     if (!derived[c]) inputs[c].resize(kChunk);
@@ -482,10 +507,22 @@ void ScopeModel::recompute_math_locked(const std::vector<bool>& affected) {
       math_apply_locked(slot, &affected, /*timed=*/false);
     }
   }
-  // The pyramid is the consumer's and the tick publishes it; the samples are written here.
+  // The pyramid is the consumer's and the tick publishes it (`republish_from()` above put its window
+  // back at `base` so that publish is one window's worth of work); the samples are written here.
 }
 
 void ScopeModel::rebuild_channels() {
+  // The trigger names a channel by its display name, which is stable across the renumbering this
+  // function *is*; the index is not. Captured and restored here rather than at the call sites
+  // because every caller renumbers and every caller needs it: adding a math channel appends a
+  // signal and shifts nothing, but removing one, or a CONFIG that reorders the stream's own
+  // signals, moves every index after it. `rebuild_locked()` then only clamps an out-of-range
+  // index to -1, and `TriggerEngine::process()` returns immediately on a channel of -1 -- so the
+  // panel went on naming the channel while nothing could ever fire again.
+  const std::string trigger_name =
+      (trigger_.channel >= 0 && trigger_.channel < static_cast<int>(channels_.size()))
+          ? channels_[static_cast<std::size_t>(trigger_.channel)].name
+          : std::string();
   channels_.clear();
   // Which channel each math channel ended up with, by name: a disabled one has none, and the
   // producer must not push a derived sample into another channel's ring.
@@ -524,6 +561,15 @@ void ScopeModel::rebuild_channels() {
     }
     channels_.push_back(std::move(ch));
   }
+
+  // A name that is no longer a channel -- its signal was disabled, or the stream stopped
+  // declaring it -- leaves the trigger unassigned, which is a wait rather than a silent
+  // mis-aim; re-enabling the signal brings it back here.
+  trigger_.channel = -1;
+  if (trigger_name.empty()) return;
+  for (std::size_t i = 0; i < channels_.size(); ++i) {
+    if (channels_[i].name == trigger_name) trigger_.channel = static_cast<int>(i);
+  }
 }
 
 void ScopeModel::rebuild_locked() {
@@ -536,22 +582,16 @@ void ScopeModel::rebuild_locked() {
   holes_.clear();
   ++plan_generation_;
 
-  std::vector<double> dts;
-  dts.reserve(channels_.size());
-  for (const ChannelInfo& c : channels_) dts.push_back(c.dt);
-
-  if (dts.empty()) {
+  if (channels_.empty()) {
     part_ = Partition{};
     store_.reset();
     return;
   }
 
-  const Partition want = plan_partition(dts, cfg_.buffer_mb * 1024.0 * 1024.0,
-                                        target_span_.load(std::memory_order_relaxed),
-                                        cfg_.relative_time);
+  const Partition want = plan_locked(target_span_.load(std::memory_order_relaxed));
   // A plan that describes the storage already allocated is cleared, not rebuilt. Allocating
-  // a store is what costs -- its rings are value-initialised, so it touches the whole
-  // `--buffer-mb` -- and most structural changes do not move the plan at all: a calibration
+  // a store is what costs -- its rings are value-initialised, so it touches all of the
+  // planned rings -- and most structural changes do not move the plan at all: a calibration
   // keeps the channel set, and so does leaving an event for the live view. Startup asked for
   // sixteen of these and eight of them planned the same buffer twice. Clearing has the same
   // meaning (`BufferStore::reset()`): the history is gone either way, which is why
@@ -570,6 +610,17 @@ void ScopeModel::rebuild_locked() {
     // the defect the line exists to name (it was fifteen of them at startup).
     std::fprintf(stderr, "[udpscope] buffer allocated: %zu channels, %.3g s span, %.0f ms\n",
                  channels_.size(), part_.span_s, double(now_ns() - t0) / 1.0e6);
+    if (part_.memory_limited) {
+      // The one line that says the request was not honoured, and why: a smaller ring than the source
+      // form promised is otherwise explained nowhere.
+      std::fprintf(stderr,
+                   "[udpscope] buffer limited to %s samples per signal (%s requested) by the %s "
+                   "memory limit; the rings take %s\n",
+                   format_samples(part_.time_capacity).c_str(),
+                   format_samples(part_.requested_samples).c_str(),
+                   format_bytes(memory_limit_bytes()).c_str(),
+                   format_bytes(part_.bytes()).c_str());
+    }
     std::fflush(stderr);
   }
 
@@ -577,6 +628,47 @@ void ScopeModel::rebuild_locked() {
   prepare_math_locked();
 }
 
+Partition ScopeModel::plan_locked(double seconds) const {
+  std::vector<double> dts;
+  dts.reserve(channels_.size());
+  for (const ChannelInfo& c : channels_) dts.push_back(c.dt);
+  return plan_partition(dts, cfg_.buffer_samples, memory_limit_bytes(), seconds, cfg_.relative_time);
+}
+
+bool ScopeModel::set_memory_limit_bytes(std::uint64_t bytes, bool replan) {
+  std::lock_guard<std::mutex> lock(mutex_);
+  const std::uint64_t previous = memory_limit_bytes_.load(std::memory_order_relaxed);
+  if (bytes == previous) return false;
+  if (channels_.empty() || !replan) {
+    memory_limit_bytes_.store(bytes, std::memory_order_relaxed);
+    return false;
+  }
+  memory_limit_bytes_.store(bytes, std::memory_order_relaxed);
+  Partition want;
+  try {
+    want = plan_locked(target_span_.load(std::memory_order_relaxed));
+  } catch (const std::exception& e) {
+    memory_limit_bytes_.store(previous, std::memory_order_relaxed);
+    std::fprintf(stderr, "[udpscope] memory limit %s refused: %s\n", format_bytes(bytes).c_str(),
+                 e.what());
+    std::fflush(stderr);
+    return false;
+  }
+  if (store_ && part_.same_storage_as(want)) {
+    // The same rings: only what the plan *says* about itself moved. Written in place, because the
+    // producer reads `part_` under the lock we hold and nothing here reallocates it.
+    part_.requested_samples = want.requested_samples;
+    part_.memory_limited = want.memory_limited;
+    return false;
+  }
+  std::fprintf(stderr, "[udpscope] memory limit %s -> %s: buffer re-planned\n",
+               format_bytes(previous).c_str(), format_bytes(bytes).c_str());
+  std::fflush(stderr);
+  rebuild_locked();
+  generation_.fetch_add(1, std::memory_order_release);
+  return true;
+}
+
 bool ScopeModel::set_target_span(double seconds) {
   if (!(seconds > 0.0)) return false;
   std::lock_guard<std::mutex> lock(mutex_);
@@ -585,10 +677,7 @@ bool ScopeModel::set_target_span(double seconds) {
   // Re-plan only if the factor moves. The planner is cheap, so ask it rather than
   // reimplementing its arithmetic here -- two expressions for the same decision is how
   // the buffer and the view end up disagreeing about the stored rate.
-  std::vector<double> dts;
-  dts.reserve(channels_.size());
-  for (const ChannelInfo& c : channels_) dts.push_back(c.dt);
-  const Partition want = plan_partition(dts, cfg_.buffer_mb * 1024.0 * 1024.0, seconds, cfg_.relative_time);
+  const Partition want = plan_locked(seconds);
   if (want.time_stride == part_.time_stride) return false;
   std::fprintf(stderr,
                "[udpscope] window %.4f s -> %.4f s: decimation %llu -> %llu, stored rate "
@@ -613,7 +702,7 @@ bool ScopeModel::is_time_signal(const std::vector<SignalInfo>& signals,
   // signal: it has stamps but no cadence of its own, because it is not data.
   // Data channels can also be declared full-array (per-element stamps), and they
   // keep a declared rate -- treating them as time signals hid every real channel.
-  if (s.time_mode == UDPS_TIME_FULL_ARRAY && s.elements() > 1 && s.sampling_rate == 0.0) {
+  if (s.time_mode == kTimeFullArray && s.elements() > 1 && s.sampling_rate == 0.0) {
     return true;
   }
   return false;
@@ -639,22 +728,8 @@ bool ScopeModel::enable_locked(std::size_t signal, bool on) {
 }
 
 void ScopeModel::rebuild_enabled_locked() {
-  // The trigger names a channel by its display name, which is stable across
-  // renumbering: when its own signal is disabled the channel vanishes (the trigger
-  // then waits, and comes back when the signal is re-enabled). Read before
-  // `rebuild_channels()`, which is what renumbers.
-  const int old_trigger = trigger_.channel;
-  const std::string trigger_name =
-      (old_trigger >= 0 && old_trigger < static_cast<int>(channels_.size()))
-          ? channels_[static_cast<std::size_t>(old_trigger)].name
-          : std::string();
+  // `rebuild_channels()` carries the trigger's channel across the renumbering by name.
   rebuild_channels();
-  trigger_.channel = -1;
-  if (!trigger_name.empty()) {
-    for (std::size_t i = 0; i < channels_.size(); ++i) {
-      if (channels_[i].name == trigger_name) trigger_.channel = static_cast<int>(i);
-    }
-  }
   rebuild_locked();
   generation_.fetch_add(1, std::memory_order_release);
 }
@@ -702,6 +777,38 @@ void ScopeModel::set_calibration(std::size_t signal, double gain, double offset)
   }
 }
 
+void ScopeModel::set_signal_unit(std::size_t signal, const std::string& unit) {
+  std::lock_guard<std::mutex> lock(mutex_);
+  if (signal >= signals_.size() || signals_[signal].math) return;
+  const std::string name = signals_[signal].name;
+  std::string shown = unit;
+  if (unit.empty()) {
+    unit_override_.erase(name);
+    const auto it = declared_unit_.find(name);
+    shown = it != declared_unit_.end() ? it->second : std::string();
+  } else {
+    unit_override_[name] = unit;
+  }
+  if (signals_[signal].unit == shown) return;
+  signals_[signal].unit = shown;
+  for (ChannelInfo& c : channels_) {
+    if (c.signal == signal) c.unit = shown;
+  }
+  generation_.fetch_add(1, std::memory_order_release);
+}
+
+std::string ScopeModel::declared_unit(std::size_t signal) {
+  std::lock_guard<std::mutex> lock(mutex_);
+  if (signal >= signals_.size()) return std::string();
+  const auto it = declared_unit_.find(signals_[signal].name);
+  return it != declared_unit_.end() ? it->second : signals_[signal].unit;
+}
+
+std::vector<std::pair<std::string, std::string>> ScopeModel::unit_overrides() {
+  std::lock_guard<std::mutex> lock(mutex_);
+  return {unit_override_.begin(), unit_override_.end()};
+}
+
 double ScopeModel::channel_dt(std::size_t channel) const {
   return channel < channels_.size() ? channels_[channel].dt : 0.0;
 }
@@ -872,9 +979,11 @@ void ScopeModel::publish_event(double pre_s, double post_s, double edge) {
   }
 
   snap->values.resize(channels_.size());
+  snap->channel_names.resize(channels_.size());
   snap->y.resize(channels_.size(), plot::Range{0.0, 0.0});
   snap->pyramids.resize(channels_.size());
   for (std::size_t c = 0; c < channels_.size(); ++c) {
+    snap->channel_names[c] = channels_[c].name;
     auto& vals = snap->values[c];
     vals.resize(static_cast<std::size_t>(n));
     if (n > 0) src.values(c).copy_from(first, n, vals.data());
@@ -899,6 +1008,24 @@ void ScopeModel::publish_event(double pre_s, double post_s, double edge) {
   // capture at the first sample past `post_s` rather than exactly on it.
   snap->pre_s = snap->stamps.empty() ? 0.0 : -static_cast<double>(snap->stamps.front());
   snap->post_s = snap->stamps.empty() ? 0.0 : static_cast<double>(snap->stamps.back());
+  // The persistence retention: what was on screen until now becomes the *newest of the older*
+  // acquisitions, and the set is cut back to the depth the panel asks for and to the retention
+  // budget. Nothing is retained at depth 1, so the default costs no memory and no copy at all.
+  if (const int depth = persist_depth_locked(); depth > 1) {
+    std::shared_ptr<const EventSnapshot> prev = event_.load(std::memory_order_relaxed);
+    if (prev != nullptr) {
+      // Only the slots the depth wants are shifted: the ones past it are the prune's business, and
+      // moving an acquisition into a slot nothing can ever read is work for a snapshot about to be
+      // dropped.
+      const std::size_t top = std::min(static_cast<std::size_t>(depth - 1), persist_.size());
+      for (std::size_t i = top; i-- > 1;) {
+        persist_[i].store(persist_[i - 1].load(std::memory_order_relaxed),
+                          std::memory_order_relaxed);
+      }
+      persist_[0].store(std::move(prev), std::memory_order_relaxed);
+    }
+  }
+  prune_persist_locked(static_cast<std::size_t>(persist_depth_locked() - 1));
   event_.store(std::move(snap), std::memory_order_release);
   // Bumped after the snapshot is in place, so a consumer that sees the new sequence
   // number sees the snapshot it counts.
@@ -944,6 +1071,48 @@ void ScopeModel::set_trigger_enabled(bool on) {
   trigger_enabled_.store(on, std::memory_order_relaxed);
 }
 
+void ScopeModel::prune_persist_locked(std::size_t keep) {
+  const std::size_t limit = std::min(keep, persist_.size());
+  const std::size_t budget = persist_budget_bytes();
+  std::size_t bytes = 0;
+  std::size_t kept = 0;
+  std::uint64_t dropped = 0;
+  bool full = false;
+  for (std::size_t i = 0; i < persist_.size(); ++i) {
+    const std::shared_ptr<const EventSnapshot> snap = persist_[i].load(std::memory_order_relaxed);
+    if (snap == nullptr) continue;
+    if (i < limit) {
+      // Either bound can cut the set: the depth the panel asks for, and the budget, which a long
+      // window on a fast stream reaches long before the seventh layer.
+      const std::size_t b = snapshot_bytes(*snap);
+      if (!full && bytes + b <= budget) {
+        bytes += b;
+        ++kept;
+        continue;
+      }
+      full = true;  // does not fit, and neither does anything older
+      // Only what the *budget* refused is counted: a slot past the depth is not a drop, it is the
+      // depth -- and counting it would make the reading say the memory was the reason when the
+      // panel's own number was.
+      ++dropped;
+    }
+    persist_[i].store(nullptr, std::memory_order_relaxed);
+  }
+  persist_count_.store(kept, std::memory_order_relaxed);
+  persist_bytes_.store(bytes, std::memory_order_relaxed);
+  persist_dropped_.store(persist_dropped_.load(std::memory_order_relaxed) + dropped,
+                         std::memory_order_relaxed);
+}
+
+void ScopeModel::set_persist_depth(int depth) {
+  const int n = std::clamp(depth, 1, kMaxPersistDepth);
+  std::lock_guard<std::mutex> lock(mutex_);
+  trigger_.persist_depth = n;
+  // Pruned here and not only at the next latch: lowering the depth is the user asking to stop
+  // paying for the layers, and a trigger that has stopped firing never reaches another publish.
+  prune_persist_locked(static_cast<std::size_t>(n - 1));
+}
+
 void ScopeModel::set_epoch_if_unset(f64 e) noexcept {
   if (epoch_ == 0.0) epoch_ = e;
 }

src/model.hpp

@@ -10,6 +10,8 @@
 
 #include <plot/data/ring_buffer.hpp>
 
+#include <algorithm>
+#include <array>
 #include <atomic>
 #include <unordered_map>
 #include <cstdint>
@@ -22,6 +24,13 @@
 
 namespace udpscope {
 
+/// `SignalInfo::time_mode` values. They equal the wire protocol's `UDPS_TIME_*`
+/// (`udps_source.cpp` static_asserts it), but the model must not name a source's own header.
+constexpr std::uint8_t kTimePacket = 0;
+constexpr std::uint8_t kTimeFullArray = 1;
+constexpr std::uint8_t kTimeFirstSample = 2;
+constexpr std::uint8_t kTimeLastSample = 3;
+
 /// One streamed signal, as the CONFIG packet described it.
 struct SignalInfo {
   std::string name;
@@ -95,9 +104,27 @@ struct Partition {
 
   /// True when a second f64 ring parallel to the clock was planned and paid for in the
   /// byte budget. Relative mode only -- in stream mode `time()` already *is* the absolute
-  /// clock and a copy would cost ~22% of the user's `--buffer-mb` for nothing.
+  /// clock and a copy would cost ~22% of the user's sample budget for nothing.
   bool abs_time = false;
 
+  /// The samples-per-signal the user asked for, as given (not rounded). `time_capacity` is what
+  /// the plan actually holds: the request rounded down to a power of two, then halved further
+  /// while the rings did not fit the memory limit. These two are readings, not storage -- they are
+  /// not in `same_storage_as()` -- so a re-plan that only moves them does not drop history.
+  u64 requested_samples = 0;
+  /// True when the memory limit, and not the power-of-two rounding, made `time_capacity` smaller than
+  /// the request: the one case the UI has to explain.
+  bool memory_limited = false;
+
+  /// The bytes the rings of this plan occupy: the time ring (twice in relative mode) plus every
+  /// value ring. This is the figure to quote and to budget against; a count of the user's
+  /// request is not, because the rings round and the limit can clip.
+  u64 bytes() const noexcept {
+    u64 total = time_capacity * sizeof(f64) * (abs_time ? 2u : 1u);
+    for (u64 c : value_capacity) total += c * sizeof(f32);
+    return total;
+  }
+
   /// Seconds between two time-base slots (the sample interval of every channel).
   double slot_dt() const noexcept { return base_dt * static_cast<double>(time_stride); }
   /// The rate samples are actually stored at, in samples per second.
@@ -128,13 +155,24 @@ struct Partition {
   }
 };
 
-/// Plans a partition for `channel_dt` cadences within `buffer_bytes`, covering at least
-/// `target_span_s` seconds of stream -- decimating (with the ingest filter) by whatever
-/// power of two that takes. Throws std::runtime_error when the budget cannot hold even
-/// one sample per channel. `with_abs_time` adds a second f64 per time slot to the budget
-/// and sets `Partition::abs_time`.
-Partition plan_partition(const std::vector<double>& channel_dt, double buffer_bytes,
-                         double target_span_s, bool with_abs_time = false);
+/// The ring length a request of `requested_samples` per signal buys: the largest power of two not
+/// above it (at least 128). The rings are powers of two, so the user's number is a ceiling.
+u64 buffer_ticks(u64 requested_samples);
+
+/// What `ticks` slots cost for `channels` unit-stride channels: the f64 time ring (twice with the
+/// absolute clock) plus one f32 ring per channel. The planner's own byte formula, for a caller
+/// that has no `Partition` yet (the source form, the probes).
+u64 planned_bytes(u64 ticks, std::size_t channels, bool with_abs_time);
+
+/// Plans a partition for `channel_dt` cadences: `samples_per_signal` slots for the time ring and for
+/// every channel, rounded down to a power of two, then halved while the rings (`planned_bytes()`)
+/// exceed `max_bytes` -- the memory limit. Covers at least `target_span_s` seconds of stream,
+/// decimating (with the ingest filter) by whatever power of two that takes. Throws
+/// std::runtime_error when even 128 slots do not fit `max_bytes`. `with_abs_time` adds a second f64
+/// per time slot to the budget and sets `Partition::abs_time`. `Partition::memory_limited` says
+/// whether the limit clipped the request.
+Partition plan_partition(const std::vector<double>& channel_dt, u64 samples_per_signal,
+                         u64 max_bytes, double target_span_s, bool with_abs_time = false);
 
 /// One of the two identical sample buffers: a shared time-base ring plus one
 /// value ring and one `ChannelBuffer` per channel.
@@ -178,7 +216,7 @@ class BufferStore {
   ///
   /// Why it exists: constructing a store *is* its cost. A ring is a
   /// `vector<std::atomic<T>>`, which is value-initialised, so building one touches every
-  /// byte of the user's `--buffer-mb` -- about 300 ms per GB, nearly all of it first-touch
+  /// byte of the planned buffer (`--buffer-samples`) -- about 300 ms per GB, nearly all of it first-touch
   /// page faults. Clearing is a count store per ring. Most structural changes (a
   /// calibration, a re-enable of what was just disabled, going back to live) re-plan to the
   /// *same* partition, and paying a second full allocation for them is what made a large
@@ -268,6 +306,15 @@ struct StreamStats {
   /// a reading of 0 beside a non-zero `holes` is exactly the honest answer until the
   /// backfill lands.
   std::atomic<std::uint64_t> backfilled{0};
+  /// Reservations refused because the counter's claim was not corroborated by the arrival
+  /// cadence, or because the hole it would book is bigger than the ring can hold. A counter
+  /// is a claim about the wire and the arrival clock is the measurement of it: a stream whose
+  /// counter does not count packets (a sample counter, say) reports a forward jump on every
+  /// datagram, and believing it booked a NaN hole per packet -- a band over the whole window
+  /// filled with samples that were never missing, which the backfill cannot repair because no
+  /// packet was ever lost. Counted here because it is otherwise *invisible*: the status bar's
+  /// `gaps` climbs either way, and only this field says the gap was refused.
+  std::atomic<std::uint64_t> gaps_refused{0};
 };
 
 /// What the plot is showing, which is one decision made once per frame: the bind, the
@@ -418,6 +465,17 @@ class ScopeModel {
   /// no channel to read it from, and the record is what a dialog must show.
   std::pair<double, double> calibration(std::size_t signal);
 
+  /// Renames the unit a streamed signal is shown, read and exported in. Stored by the signal's *name*
+  /// like the calibration, and re-applied to every later CONFIG, so a rename survives a reconnect.
+  /// An empty `unit` removes the override and restores the unit the stream declared. A math channel's
+  /// unit belongs to its graph and is ignored here. Bumps `generation()` when it changed something,
+  /// which is what makes the panels re-read the signal list.
+  void set_signal_unit(std::size_t signal, const std::string& unit);
+  /// The unit the stream declared for that signal, whatever the user renamed it to.
+  std::string declared_unit(std::size_t signal);
+  /// The renames in force, `{name, unit}`, for the session file.
+  std::vector<std::pair<std::string, std::string>> unit_overrides();
+
   std::size_t channel_count() const noexcept { return channels_.size(); }
   const Partition& partition() const noexcept { return part_; }
 
@@ -502,6 +560,55 @@ class ScopeModel {
   /// while the latch count keeps answering "how many events fired".
   std::uint64_t event_seq() const noexcept { return event_seq_.load(std::memory_order_acquire); }
 
+  // --- persistence ----------------------------------------------------------
+  /// The acquisitions retained for the persistence display, newest first: `persist_event(1)` is
+  /// the event one latch back, `(2)` the one before that. Null for an age nobody kept.
+  ///
+  /// Read **without a lock**, like `event()`: the producer publishes these in `publish_event()`
+  /// with the same atomic-`shared_ptr` discipline, and a snapshot is immutable and shared, so a
+  /// reader holds it alive for as long as it draws it. What the *ring* would have given is not
+  /// needed afterwards -- a retained snapshot is a whole window copied out of it.
+  std::shared_ptr<const EventSnapshot> persist_event(std::size_t age) const noexcept {
+    if (age < 1 || age > persist_.size()) return nullptr;
+    return persist_[age - 1].load(std::memory_order_acquire);
+  }
+  /// How many acquisitions are retained right now: what the depth asks for, or fewer -- never more
+  /// -- when the retention budget cut the set short. A reading, so it is counted as the slots that
+  /// hold a snapshot rather than derived from the depth.
+  std::size_t persist_count() const noexcept {
+    return persist_count_.load(std::memory_order_relaxed);
+  }
+  /// What those snapshots hold in bytes, and how many acquisitions the *budget* -- as against the
+  /// depth -- has dropped. Both are producer-written and read as readings.
+  std::size_t persist_bytes() const noexcept {
+    return persist_bytes_.load(std::memory_order_relaxed);
+  }
+  std::uint64_t persist_dropped() const noexcept {
+    return persist_dropped_.load(std::memory_order_relaxed);
+  }
+  /// The bytes persistence may retain, which is the rings' own planned byte total
+  /// (`Partition::bytes()`): the snapshots are copies *of* what the rings hold, so holding as much
+  /// again as the buffer does is the honest ceiling for a display of it -- and it is the bound that
+  /// cannot be driven into an OOM by a long window on a fast stream, whatever depth the panel asks
+  /// for. Zero until a stream has planned a buffer. Read under `mutex()`, like `partition()`.
+  std::size_t persist_budget_bytes() const noexcept {
+    return static_cast<std::size_t>(part_.bytes());
+  }
+
+  /// Sets how many acquisitions the persistence display keeps, clamped to `kMaxPersistDepth`, and
+  /// prunes the retained set to it **at once**: lowering the depth is a user asking to stop paying
+  /// for the layers, and the next latch -- when the retention would otherwise catch up -- may never
+  /// come on a trigger that has stopped firing.
+  ///
+  /// Takes `mutex()` itself; do not call it holding the lock.
+  void set_persist_depth(int depth);
+
+  /// How many acquisitions the persistence display keeps: the depth, clamped to the cap. Reading
+  /// `trigger()` needs the lock, which every caller of this already holds.
+  int persist_depth_locked() const noexcept {
+    return std::clamp(trigger_.persist_depth, 1, kMaxPersistDepth);
+  }
+
   /// Publishes the live buffer's new samples to its `ChannelBuffer`s.
   void acquire_all();
 
@@ -604,6 +711,22 @@ class ScopeModel {
   /// `mutex()` itself; do not call it holding the lock.
   /// Returns true when the buffer was rebuilt.
   bool set_target_span(double seconds);
+
+  /// The memory limit the planner honours, in bytes. Starts as `Config::memory_limit_mb` and is the
+  /// one planner input that changes while the application runs (the preferences). Atomic so the
+  /// status and the probes can read it without the lock.
+  std::uint64_t memory_limit_bytes() const noexcept {
+    return memory_limit_bytes_.load(std::memory_order_relaxed);
+  }
+  /// Changes the memory limit and re-plans. The buffer is rebuilt -- and the history dropped -- only
+  /// when the new limit changes the *storage* (`Partition::same_storage_as()`): a limit that still
+  /// leaves room for the plan updates `Partition::memory_limited` in place and costs nothing.
+  /// Returns true when the buffer was rebuilt. Takes `mutex()` itself; do not call it holding the
+  /// lock. A limit too small for even 128 slots per channel is refused (returns false, keeps the old
+  /// limit) and said on stderr.
+  /// With `replan` false the limit is only stored, for the next plan: a file or a replayed event
+  /// lives in the buffer, and re-planning it would clear what the user is looking at.
+  bool set_memory_limit_bytes(std::uint64_t bytes, bool replan = true);
   double target_span() const noexcept { return target_span_.load(std::memory_order_relaxed); }
 
   /// Trigger state for the UI, published by the acquisition thread. Atomics
@@ -632,6 +755,20 @@ class ScopeModel {
   /// `mutex()` and the producer holds that lock for all of `on_data`, so a plain read under the
   /// lock is correct, and a reconnect with an identical CONFIG is a re-plan this sees and the
   /// stride/channel-count comparison does not.
+  /// A restarted client is a **new stream**, and the retained history belongs to the old one: its clock may
+  /// sit behind the stamps the previous stream wrote, and the producer's monotonic guard would then pin
+  /// every later packet flat at the old value -- the `ring=[x..x]` a display that never moves shows.
+  /// `reset()` is what the data-path invariants require of a rebuild (nothing of the old history behind),
+  /// and `plan_generation_` moving is what tells the producer to drop the state tied to the old store.
+  void reset_stream() {
+    std::lock_guard<std::mutex> lock(mutex_);
+    // Null before the first CONFIG has planned anything: `Acquisition::start()` calls this, and at start-up
+    // there is no store yet. Dereferencing it there was a SIGSEGV with no output at all.
+    if (store_ != nullptr) store_->reset();
+    ++plan_generation_;
+    ++generation_;
+  }
+
   unsigned plan_generation() const noexcept { return plan_generation_; }
 
  private:
@@ -653,7 +790,14 @@ class ScopeModel {
   /// so a window change that moves the decimation re-prepares the filters exactly as an edit does.
   void prepare_math_locked();
 
+  /// Plans the partition for the current channels at `seconds` of window with the current sample
+  /// budget and memory limit. The one place the planner's inputs are assembled, so the re-plan on a
+  /// window change, a structural change and a memory-limit change cannot disagree. Throws what
+  /// `plan_partition()` throws. Caller holds `mutex()`.
+  Partition plan_locked(double seconds) const;
+
   Config cfg_;
+  std::atomic<std::uint64_t> memory_limit_bytes_{0};
   std::vector<SignalInfo> signals_;
   std::vector<ChannelInfo> channels_;
   // --- math channels --------------------------------------------------------
@@ -719,9 +863,25 @@ class ScopeModel {
   std::atomic<double> capture_edge_{0.0};
   std::atomic<std::shared_ptr<const EventSnapshot>> event_;  ///< the event on screen
   std::atomic<std::shared_ptr<const EventSnapshot>> pause_view_;  ///< the view frozen at pause
+  /// The retention behind `persist_event()`: one slot per *previous* acquisition, newest first, so
+  /// slot 0 is the event one latch back. `kMaxPersistDepth - 1` of them, because the acquisition on
+  /// screen is `event_` itself and is not retained a second time. Written by the producer in
+  /// `publish_event()` and by `set_persist_depth()`, both under `mutex()`; read without it.
+  std::array<std::atomic<std::shared_ptr<const EventSnapshot>>, kMaxPersistDepth - 1> persist_{};
+  /// The readings `persist_count()`/`persist_bytes()`/`persist_dropped()` answer with, maintained
+  /// where the slots are written.
+  std::atomic<std::size_t> persist_count_{0};
+  std::atomic<std::size_t> persist_bytes_{0};
+  std::atomic<std::uint64_t> persist_dropped_{0};
+  /// Drops the retained snapshots past `keep` (0 empties the set) and recounts the readings.
+  /// Caller holds `mutex()`.
+  void prune_persist_locked(std::size_t keep);
   std::atomic<bool> paused_{false};
   /// Per-signal-name calibration (see `set_calibration`).
   std::unordered_map<std::string, std::pair<double, double>> calibration_;
+  /// Per-signal-name unit renames (see `set_signal_unit`) and the units the stream declared.
+  std::unordered_map<std::string, std::string> unit_override_;
+  std::unordered_map<std::string, std::string> declared_unit_;
   std::atomic<std::uint64_t> event_seq_{0};
   std::atomic<double> display_epoch_{0.0};
   std::atomic<bool> trigger_armed_{false};

src/plot_host.cpp

@@ -5,6 +5,7 @@
 
 #include <algorithm>
 #include <cmath>
+#include <span>
 
 namespace udpscope {
 namespace {
@@ -67,9 +68,32 @@ constexpr float kMeasureDashOff = 4.0f;
 /// a box, so there was a widget gap; a figure tiles its viewport, and without a gap two
 /// stacked frames read as one tall plot with a line through it.
 constexpr plot::f32 kRowGap = 6.0f;
+/// The gap between two cells of a split row, device pixels: the same as the rows', so the
+/// plots read as a grid.
+constexpr plot::f32 kColGap = 6.0f;
+
+/// The suffix that names a persistence layer, in the accumulate path's own vocabulary --
+/// ` (A)`, ` (B)`, ` #4` -- so that `layer_base_name()` takes it back off, and the signal list, the
+/// colour resolver, the measurements and the layout writer all keep seeing one signal where the
+/// plot draws several traces of it.
+std::string layer_suffix(int age) {
+  if (age == 1) return " (A)";
+  if (age == 2) return " (B)";
+  return " #" + std::to_string(age + 1);
+}
 
 }  // namespace
 
+float RowSet::persist_alpha(int age) noexcept {
+  // Half per acquisition, so the seventh is 1/128 -- and halves, not a slope, because that is what
+  // "exponential decay" means and because it is the one schedule that can be read off a line of
+  // numbers: 1, 0.5, 0.25, 0.125. It does not depend on the depth, so raising N adds dimmer
+  // acquisitions instead of restating the ones already on screen.
+  float a = 1.0f;
+  for (int i = 0; i < age; ++i) a *= 0.5f;
+  return a;
+}
+
 std::string layer_base_name(const std::string& name) {
   const std::size_t a = name.rfind(" (");
   if (a != std::string::npos && a + 3 < name.size() && name[a + 3] == ')' &&
@@ -133,11 +157,56 @@ void RowSet::clear_signal_color(const std::string& signal) {
 
 RowSet::RowSet() { rebuild_all(); }
 
+int RowSet::cells_in_row(int fr) const {
+  return fr >= 0 && fr < figure_row_count() ? cells_per_row_[static_cast<std::size_t>(fr)] : 0;
+}
+
+int RowSet::first_plot_of_row(int fr) const {
+  int p = 0;
+  for (int r = 0; r < fr && r < figure_row_count(); ++r) p += cells_per_row_[static_cast<std::size_t>(r)];
+  return p;
+}
+
+int RowSet::figure_row_of(int plot) const {
+  if (plot < 0 || plot >= rows_) return -1;
+  int p = 0;
+  for (int r = 0; r < figure_row_count(); ++r) {
+    p += cells_per_row_[static_cast<std::size_t>(r)];
+    if (plot < p) return r;
+  }
+  return -1;
+}
+
+int RowSet::cell_of(int plot) const {
+  const int fr = figure_row_of(plot);
+  return fr < 0 ? -1 : plot - first_plot_of_row(fr);
+}
+
+const std::vector<float>& RowSet::cell_weights(int fr) const {
+  static const std::vector<float> none;
+  return fr >= 0 && fr < static_cast<int>(cell_weights_.size())
+             ? cell_weights_[static_cast<std::size_t>(fr)]
+             : none;
+}
+
+std::string RowSet::plot_label(int plot) const {
+  const int fr = figure_row_of(plot);
+  if (fr < 0) return std::to_string(plot + 1);
+  if (cells_per_row_[static_cast<std::size_t>(fr)] == 1) return std::to_string(fr + 1);
+  return std::to_string(fr + 1) + static_cast<char>('a' + cell_of(plot));
+}
+
 void RowSet::set_row_count(int rows) {
   const int want = std::clamp(rows, 1, kMaxRows);
-  if (want == rows_) return;
+  const bool all_single =
+      std::all_of(cells_per_row_.begin(), cells_per_row_.end(), [](int c) { return c == 1; });
+  if (want == rows_ && all_single) return;
+  // `n` single-cell rows. The plots keep their flattened slots (and so their contents), which is
+  // what the old "n rows" meant.
   rows_ = want;
-  // A `Figure`'s row count is fixed at construction, so a new count is a new figure.
+  cells_per_row_.assign(static_cast<std::size_t>(want), 1);
+  cell_weights_.assign(static_cast<std::size_t>(want), {});
+  // A `Figure`'s shape is fixed at construction, so a new count is a new figure.
   rebuild_all();
 }
 
@@ -146,6 +215,11 @@ void RowSet::carry_row(Row& dst, const Row& src) {
   dst.name = src.name;
   dst.channel = src.channel;
   dst.color_index = src.color_index;
+  // A layer travels with the slot that draws it: it *is* part of what that slot holds. The tick's
+  // `sync_layers()` re-plans them all next frame in any case, which is what heals a row that has
+  // moved under a plan made for the old one.
+  dst.layer = src.layer;
+  dst.slot_alpha = src.slot_alpha;
 
   dst.ruler_y = src.ruler_y;
   dst.ruler_b_y = src.ruler_b_y;
@@ -161,39 +235,152 @@ void RowSet::clear_row(Row& r) {
   r.name = {};
   r.channel = {-1, -1, -1, -1};
   r.color_index = {0, 1, 2, 3};
+  r.layer = {0, 0, 0, 0};
+  r.slot_alpha = {1.0f, 1.0f, 1.0f, 1.0f};
   r.ruler_y = 0.0;
   for (SlotSeries& s : r.slots) s.bind(nullptr);
 }
 
 bool RowSet::insert_row(int at) {
   if (rows_ >= kMaxRows) return false;
-  const int pos = std::clamp(at, 0, rows_);
+  const int fr = std::clamp(at, 0, figure_row_count());
+  const int pos = first_plot_of_row(fr);
   for (int i = rows_; i > pos; --i) carry_row(row(i), row(i - 1));
   clear_row(row(pos));
   ++rows_;
+  cells_per_row_.insert(cells_per_row_.begin() + fr, 1);
+  cell_weights_.insert(cell_weights_.begin() + fr, std::vector<float>{});
+  // Keep row_weights_ in step with the figure row count: the new row gets the default
+  // weight (1.0) at its position so the existing rows keep theirs.
+  if (!row_weights_.empty()) {
+    row_weights_.resize(static_cast<std::size_t>(figure_row_count() - 1), 1.0f);
+    row_weights_.insert(row_weights_.begin() + fr, 1.0f);
+  }
   rebuild_all();
   return true;
 }
 
 bool RowSet::remove_row(int at) {
-  if (rows_ <= 1 || at < 0 || at >= rows_) return false;
-  for (int i = at; i + 1 < rows_; ++i) carry_row(row(i), row(i + 1));
-  --rows_;
-  clear_row(row(rows_));
+  if (figure_row_count() <= 1 || at < 0 || at >= figure_row_count()) return false;
+  const int pos = first_plot_of_row(at);
+  const int n = cells_per_row_[static_cast<std::size_t>(at)];
+  // The rows below move up by the removed row's cell count; the `n` slots freed at the end go back
+  // to empty.
+  for (int i = pos; i + n < rows_; ++i) carry_row(row(i), row(i + n));
+  for (int i = rows_ - n; i < rows_; ++i) clear_row(row(i));
+  rows_ -= n;
+  cells_per_row_.erase(cells_per_row_.begin() + at);
+  cell_weights_.erase(cell_weights_.begin() + at);
+  // Keep row_weights_ in step: erase the removed row's weight so the surviving rows keep theirs.
+  if (static_cast<std::size_t>(at) < row_weights_.size()) {
+    row_weights_.erase(row_weights_.begin() + at);
+  }
   rebuild_all();
   return true;
 }
 
+bool RowSet::insert_cell(int fr, int at) {
+  if (fr < 0 || fr >= figure_row_count()) return false;
+  if (cells_per_row_[static_cast<std::size_t>(fr)] >= kMaxCellsPerRow || rows_ >= kMaxRows) {
+    return false;
+  }
+  const int n = cells_per_row_[static_cast<std::size_t>(fr)];
+  const int k = std::clamp(at, 0, n);
+  const int p = first_plot_of_row(fr) + k;
+  for (int i = rows_; i > p; --i) carry_row(row(i), row(i - 1));
+  clear_row(row(p));
+  // The row's rulers belong to the new cell as well (they are one pair for the whole row): taken from
+  // a neighbour that is not the new cell, which sits at `p` and so cannot be its own source.
+  {
+    const Row& src = row(k == 0 ? p + 1 : first_plot_of_row(fr));
+    row(p).ruler_y = src.ruler_y;
+    row(p).ruler_b_y = src.ruler_b_y;
+  }
+  ++rows_;
+  ++cells_per_row_[static_cast<std::size_t>(fr)];
+  auto& w = cell_weights_[static_cast<std::size_t>(fr)];
+  if (!w.empty()) {
+    // The new cell takes the mean share, so it neither dwarfs nor vanishes beside its neighbours.
+    float mean = 0.0f;
+    for (const float v : w) mean += v;
+    mean /= static_cast<float>(w.size());
+    w.insert(w.begin() + std::min<int>(k, static_cast<int>(w.size())), mean);
+  }
+  rebuild_all();
+  return true;
+}
+
+bool RowSet::remove_cell(int plot) {
+  const int fr = figure_row_of(plot);
+  if (fr < 0) return false;
+  if (cells_per_row_[static_cast<std::size_t>(fr)] == 1) {
+    return remove_row(fr);  // false when it is the last row
+  }
+  for (int i = plot; i + 1 < rows_; ++i) carry_row(row(i), row(i + 1));
+  --rows_;
+  clear_row(row(rows_));
+  const int k = plot - first_plot_of_row(fr);
+  --cells_per_row_[static_cast<std::size_t>(fr)];
+  auto& w = cell_weights_[static_cast<std::size_t>(fr)];
+  if (cells_per_row_[static_cast<std::size_t>(fr)] < 2) {
+    w.clear();
+  } else if (k < static_cast<int>(w.size())) {
+    w.erase(w.begin() + k);
+  }
+  rebuild_all();
+  return true;
+}
+
+void RowSet::set_cell_weights(int fr, std::vector<float> w) {
+  if (fr < 0 || fr >= figure_row_count()) return;
+  cell_weights_[static_cast<std::size_t>(fr)] = std::move(w);
+  if (figure_ != nullptr) apply_cell_weights();
+}
+
+void RowSet::set_cells_per_row(std::vector<int> cells) {
+  std::vector<int> next;
+  int total = 0;
+  for (int c : cells) {
+    c = std::clamp(c, 1, kMaxCellsPerRow);
+    if (total + c > kMaxRows) c = kMaxRows - total;
+    if (c < 1) break;
+    next.push_back(c);
+    total += c;
+  }
+  if (next.empty()) {
+    next.push_back(1);
+    total = 1;
+  }
+  cells_per_row_ = std::move(next);
+  cell_weights_.assign(cells_per_row_.size(), {});
+  rows_ = total;
+  rebuild_all();
+}
+
 void RowSet::install(Row& r, int /*row_index*/, plot::Plot& p) {
   r.plot = &p;
   r.axis_x = r.plot->add_x_axis(
       {"", {-1.0, 1.0}, true, plot::AxisPlace::Bottom, false, plot::TickFormat::Time});
   r.axis_y = r.plot->add_y_axis(
       {"", {-1.0, 1.0}, true, plot::AxisPlace::Left, false, plot::TickFormat::Si});
-  for (int s = 0; s < kSlotsPerRow; ++s) {
+  // Traces are drawn in the order they were created, and a `Plot` cannot reorder them: the
+  // *dimmest* traces are created first and a signal's own trace last, so the newest acquisition is
+  // the ink on top. A layer drawn over the event would take its colour out of the event's own trace
+  // wherever the two agree -- the opposite of what a persistence display shows.
+  std::array<int, kSlotsPerRow> order{};
+  for (int s = 0; s < kSlotsPerRow; ++s) order[static_cast<std::size_t>(s)] = s;
+  std::stable_sort(order.begin(), order.end(), [&r](int a, int b) {
+    return r.slot_alpha[static_cast<std::size_t>(a)] < r.slot_alpha[static_cast<std::size_t>(b)];
+  });
+  for (const int s : order) {
     const std::size_t i = static_cast<std::size_t>(s);
-    r.plot->add_trace({&r.slots[i], signal_color(r.signal_name[i], r.color_index[i]), 1.2f,
-                       r.axis_x, r.axis_y, r.name[i]});
+    plot::Color color = signal_color(r.signal_name[i], r.color_index[i]);
+    // The slot's own brightness times the figure-wide one the group views set: a persistence
+    // layer's decay and an accumulation's translucency are the same knob, and `set_trace_alpha()`
+    // is what reads it here. It was set and never read before, which is why an accumulation's
+    // traces were opaque.
+    color.a = r.slot_alpha[i] * trace_alpha_;
+    r.plot->add_trace({&r.slots[i], color, 1.2f, r.axis_x, r.axis_y, r.name[i]});
   }
   r.cursor_a = r.plot->add_cursor(0.0, plot::Color::hex(kCursorAColor));
   r.cursor_b = r.plot->add_cursor(0.0, plot::Color::hex(kCursorBColor));
@@ -261,14 +448,40 @@ void RowSet::set_row_weights(std::vector<float> weights) {
 
 void RowSet::apply_row_weights() {
   if (row_weights_.empty() || figure_ == nullptr) return;
-  row_weights_.resize(static_cast<std::size_t>(rows_), 1.0f);
+  row_weights_.resize(static_cast<std::size_t>(figure_row_count()), 1.0f);
   (void)figure_->set_row_weights(row_weights_);
 }
 
+void RowSet::apply_cell_weights() {
+  if (figure_ == nullptr) return;
+  cell_weights_.resize(cells_per_row_.size());
+  for (int fr = 0; fr < figure_row_count(); ++fr) {
+    auto& w = cell_weights_[static_cast<std::size_t>(fr)];
+    const int n = cells_per_row_[static_cast<std::size_t>(fr)];
+    if (n < 2) {
+      w.clear();
+      continue;
+    }
+    if (w.empty()) {
+      figure_->clear_cell_weights(static_cast<plot::u32>(fr));
+      continue;
+    }
+    w.resize(static_cast<std::size_t>(n), 1.0f);
+    (void)figure_->set_cell_weights(static_cast<plot::u32>(fr), w);
+  }
+}
+
 void RowSet::rebuild_all() {
-  figure_ = std::make_unique<plot::Figure>(static_cast<plot::u32>(rows_));
+  const std::vector<plot::u32> cells(cells_per_row_.begin(), cells_per_row_.end());
+  figure_ = std::make_unique<plot::Figure>(std::span<const plot::u32>(cells));
   figure_->set_row_gap(kRowGap);
+  figure_->set_col_gap(kColGap);
+  // The cells of a split row are one plot with a vertical divider, not unrelated plots: they share
+  // one y range and auto state, and only the first draws the y axis. Before `install()`, which adds
+  // the axes the figure enrols; a row of one cell is never a group, so nothing changes for it.
+  figure_->set_share_row_y(true);
   apply_row_weights();
+  apply_cell_weights();
   x_group_ = figure_->add_x_link();
   for (int i = 0; i < kMaxRows; ++i) {
     Row& r = row(i);
@@ -278,6 +491,13 @@ void RowSet::rebuild_all() {
       continue;
     }
     install(r, i, figure_->plot(static_cast<plot::u32>(i)));
+    // A ruler is the row's (its y axis is shared), so every cell of a split row holds the first
+    // cell's values -- including a cell a restructure put next to one it had nothing to do with.
+    if (const int fr = figure_row_of(i); fr >= 0 && cell_of(i) > 0) {
+      const Row& first = row(first_plot_of_row(fr));
+      r.ruler_y = first.ruler_y;
+      r.ruler_b_y = first.ruler_b_y;
+    }
     place_cursors(r);
     if (trigger_marker_on_) {
       r.plot->set_cursor_x(r.trigger_marker, trigger_marker_x_, plot::CursorPlacement::Free);
@@ -320,9 +540,132 @@ void RowSet::assign(int row_index, int slot, std::string signal_name,
   r.channel[s] = -1;  // re-resolved by the next bind()
   r.name[s] = std::move(display_name);
   r.color_index[s] = color_index;
+  // Whatever the slot held, it is a *signal's* trace now: a drop onto a slot a persistence layer
+  // was using is the user's arrangement, and the tick's plan moves the layers around it next frame.
+  r.layer[s] = 0;
+  r.slot_alpha[s] = 1.0f;
   row_dirty_[static_cast<std::size_t>(row_index)] = true;
 }
 
+void RowSet::assign_layer(int row_index, int slot, std::string signal_name,
+                          std::string display_name, int color_index, int age, float alpha) {
+  assign(row_index, slot, std::move(signal_name), std::move(display_name), color_index);
+  if (row_index < 0 || row_index >= kMaxRows || slot < 0 || slot >= kSlotsPerRow) return;
+  Row& r = row(row_index);
+  const std::size_t s = static_cast<std::size_t>(slot);
+  r.layer[s] = age;
+  r.slot_alpha[s] = alpha;
+  row_dirty_[static_cast<std::size_t>(row_index)] = true;
+}
+
+void RowSet::clear_layers() {
+  for (int i = 0; i < kMaxRows; ++i) {
+    Row& r = row(i);
+    for (int s = 0; s < kSlotsPerRow; ++s) {
+      const std::size_t si = static_cast<std::size_t>(s);
+      if (r.layer[si] == 0) continue;
+      assign(i, s, "", "", r.color_index[si]);
+    }
+  }
+}
+
+int RowSet::sync_layers(int depth, int* want) {
+  const int ages = std::clamp(depth, 1, kMaxPersistDepth) - 1;
+  // What each slot should hold: 0 a signal's own trace (kept as it is), -1 free, >0 a layer age.
+  std::array<std::array<int, kSlotsPerRow>, kMaxRows> plan{};
+  std::array<std::array<std::string, kSlotsPerRow>, kMaxRows> names{};
+  int wanted = 0;
+  for (int r = 0; r < rows_; ++r) {
+    Row& row_state = row(r);
+    for (int s = 0; s < kSlotsPerRow; ++s) {
+      const std::size_t si = static_cast<std::size_t>(s);
+      // A layer slot is free for re-planning; a signal's own trace is not.
+      plan[static_cast<std::size_t>(r)][si] =
+          row_state.layer[si] > 0 ? -1 : (row_state.signal_name[si].empty() ? -1 : 0);
+    }
+  }
+  // Layer by layer, as the accumulate path fills its own: age 1 for every signal first, then age 2,
+  // so a row with room for two layers draws the *sharper* one for each of its signals rather than
+  // four ages of the first one.
+  for (int age = 1; age <= ages; ++age) {
+    for (int r = 0; r < rows_; ++r) {
+      const std::size_t ri = static_cast<std::size_t>(r);
+      Row& row_state = row(r);
+      for (int s = 0; s < kSlotsPerRow; ++s) {
+        const std::size_t si = static_cast<std::size_t>(s);
+        if (plan[ri][si] != 0) continue;
+        ++wanted;
+        int target = -1;
+        for (int t = 0; t < kSlotsPerRow; ++t) {
+          if (plan[ri][static_cast<std::size_t>(t)] == -1) {
+            target = t;
+            break;
+          }
+        }
+        if (target < 0) continue;  // this row is full: it persists as far as it can
+        const std::size_t ti = static_cast<std::size_t>(target);
+        plan[ri][ti] = age;
+        names[ri][ti] = row_state.signal_name[si] + layer_suffix(age);
+      }
+    }
+  }
+  int placed = 0;
+  for (int r = 0; r < rows_; ++r) {
+    const std::size_t ri = static_cast<std::size_t>(r);
+    Row& row_state = row(r);
+    for (int s = 0; s < kSlotsPerRow; ++s) {
+      const std::size_t si = static_cast<std::size_t>(s);
+      const int now = plan[ri][si];
+      const int had = row_state.layer[si];
+      if (now > 0) {
+        ++placed;
+        if (had == now && row_state.signal_name[si] == names[ri][si]) continue;  // already right
+        assign_layer(r, s, names[ri][si], names[ri][si], row_state.color_index[si], now,
+                     persist_alpha(now));
+      } else if (had > 0) {
+        assign(r, s, "", "", row_state.color_index[si]);  // nothing wants this slot any more
+      }
+    }
+  }
+  if (want != nullptr) *want = wanted;
+  return placed;
+}
+
+int RowSet::layer_of(int row_index, int slot) const {
+  if (row_index < 0 || row_index >= kMaxRows || slot < 0 || slot >= kSlotsPerRow) return 0;
+  return row(row_index).layer[static_cast<std::size_t>(slot)];
+}
+
+float RowSet::slot_alpha_of(int row_index, int slot) const {
+  if (row_index < 0 || row_index >= kMaxRows || slot < 0 || slot >= kSlotsPerRow) return 1.0f;
+  return row(row_index).slot_alpha[static_cast<std::size_t>(slot)];
+}
+
+int RowSet::layer_slots() const {
+  int n = 0;
+  for (int i = 0; i < kMaxRows; ++i) {
+    const Row& r = row(i);
+    for (int s = 0; s < kSlotsPerRow; ++s) {
+      if (r.layer[static_cast<std::size_t>(s)] > 0) ++n;
+    }
+  }
+  return n;
+}
+
+std::vector<std::pair<int, float>> RowSet::row_layers(int row_index) const {
+  std::vector<std::pair<int, float>> out;
+  if (row_index < 0 || row_index >= kMaxRows) return out;
+  const Row& r = row(row_index);
+  for (int s = 0; s < kSlotsPerRow; ++s) {
+    const std::size_t si = static_cast<std::size_t>(s);
+    if (r.layer[si] > 0) out.push_back({r.layer[si], r.slot_alpha[si]});
+  }
+  // Oldest first: the order the decay has to read in.
+  std::sort(out.begin(), out.end(),
+            [](const auto& a, const auto& b) { return a.first > b.first; });
+  return out;
+}
+
 bool RowSet::slot_bound(int row_index, int slot) const {
   if (row_index < 0 || row_index >= kMaxRows || slot < 0 || slot >= kSlotsPerRow) return false;
   return !row(row_index).signal_name[static_cast<std::size_t>(slot)].empty();
@@ -348,9 +691,15 @@ void RowSet::bind(ScopeModel& model, DisplayMode mode) {
       // Resolve the stable identity every frame: the channel list is rebuilt (and
       // renumbered) whenever a signal is enabled, disabled or re-described, and a
       // stored index would then point at a different signal's channel.
+      //
+      // A persistence layer resolves the name *under its suffix*: `sine (A)` is `sine`, one
+      // acquisition back, and it is the same signal's trace -- so it is acquired (or not) with its
+      // signal, drawn in its colour, and counted by nothing that counts signals.
+      const std::string base_name =
+          r.layer[si] > 0 ? layer_base_name(r.signal_name[si]) : r.signal_name[si];
       int signal_index = -1;
       for (std::size_t k = 0; k < signals.size(); ++k) {
-        if (signals[k].name == r.signal_name[si]) {
+        if (signals[k].name == base_name) {
           signal_index = static_cast<int>(k);
           break;
         }
@@ -364,6 +713,36 @@ void RowSet::bind(ScopeModel& model, DisplayMode mode) {
           }
         }
       }
+      if (r.layer[si] > 0) {
+        // A layer holds no channel: every reader that asks "is this slot a trace of a signal"
+        // -- the trace counts, the cursors pane's `mix` mode, the measurement marks, the layout
+        // writer -- tests `channel >= 0`, so a layer is invisible to all of them by construction.
+        r.channel[si] = -1;
+        // It draws only while a *snapshot* is on screen, and only if its signal is still acquired
+        // (switching a signal off takes its traces off every plot, layers included), and it
+        // resolves its channel **by name inside the snapshot**: the channel list may have been
+        // rebuilt and renumbered many times since that acquisition was cut, which is exactly why
+        // the trigger engine names its channel too.
+        std::shared_ptr<const EventSnapshot> snap;
+        if (channel >= 0 && (mode == DisplayMode::Held || mode == DisplayMode::Capturing)) {
+          snap = model.persist_event(static_cast<std::size_t>(r.layer[si]));
+        }
+        std::size_t layer_channel = snap != nullptr ? snap->channel_names.size() : 0;
+        if (snap != nullptr) {
+          for (std::size_t c = 0; c < snap->channel_names.size(); ++c) {
+            if (snap->channel_names[c] == base_name) {
+              layer_channel = c;
+              break;
+            }
+          }
+        }
+        if (snap != nullptr && layer_channel < snap->values.size()) {
+          r.slots[si].bind_event(std::move(snap), layer_channel);
+        } else {
+          r.slots[si].bind(nullptr);
+        }
+        continue;
+      }
       r.channel[si] = channel;
       if (channel < 0) {
         // Its signal is present but not acquired: keep the identity (so enabling it
@@ -715,10 +1094,11 @@ bool RowSet::update_time_labels() {
     // millisecond-scale window shows. `x_origin_` is read back below for the caption.
     r.plot->set_x_axis_origin_from_range(r.axis_x, relative_x_);
     if (!relative_x_) r.plot->set_x_axis_origin(r.axis_x, 0.0);
-    // The caption belongs with the labels, which a figure draws once, on the bottom row (the
-    // one whose x axis is the figure's). Every other row gets an empty one, which draws nothing.
-    const bool bottom = i == rows_ - 1;
-    if (!relative_x_ || !bottom) {
+    // The caption belongs with the labels, so it goes on every plot whose x strip draws them: the
+    // bottom row's, and any row above it that carries a strip of its own (a split row whose columns
+    // differ from the row below's; see `Figure`'s x-axis rule). The plots without labels get an empty
+    // one, which draws nothing.
+    if (!relative_x_ || !plot::x_strip_has_labels(r.plot->x_strip_mode())) {
       r.plot->set_x_note("");
       continue;
     }
@@ -745,7 +1125,7 @@ void RowSet::hold_pinned_window() {
   // and a following group would re-derive the window from a live edge on the next layout --
   // ignoring the pin altogether.
   figure_->set_x_link_follow(x_group_, plot::XFollow::Off);
-  const plot::Range pin{-pinned_pre_, pinned_post_};
+  const plot::Range pin = pinned_range();
   // The *request*: what the user's gesture left on the row's own axis. A member's `set_x_range`
   // -- what the controller writes -- is not adopted into the group while the group is not
   // following, so reading the group here only ever saw the previous clamp's answer and the wheel
@@ -753,11 +1133,21 @@ void RowSet::hold_pinned_window() {
   // statement, which is what keeps a fresh pin (`pin_event_window()`, `pin_pause_window()`, both
   // of which write the group in this same tick) from being reverted to the member's stale window.
   plot::Range now = figure_->x_link_range(x_group_);
-  if (rows_ > 0 && row(0).plot != nullptr) {
-    const plot::Range member = row(0).plot->x_range(row(0).axis_x);
+  // Any plot's member may carry the gesture: the controller writes the plot under the pointer, and an x
+  // label strip is a plot's own (the bottom row's, or a row above it whose columns differ), so reading
+  // plot 0 alone made a zoom or pan on every other plot's axis vanish when the next statement of the pin
+  // went over it. Every member was last written with `pinned_stated_` (the group push), so the first
+  // one that differs is the gesture; the same clamp below applies whichever plot it came from.
+  for (int i = 0; i < rows_; ++i) {
+    Row& r = row(i);
+    if (r.plot == nullptr) continue;
+    const plot::Range member = r.plot->x_range(r.axis_x);
     const bool member_is_ours = std::abs(member.min - pinned_stated_.min) < 1e-12 &&
                                 std::abs(member.max - pinned_stated_.max) < 1e-12;
-    if (!member_is_ours) now = member;
+    if (!member_is_ours) {
+      now = member;
+      break;
+    }
   }
   const double pin_span = pin.span();
   // **A zoom *in* is allowed.** The rule is that the view may not leave the time window, and a
@@ -818,6 +1208,11 @@ bool RowSet::event_data_window(double& lo, double& hi) const {
     const Row& r = row(i);
     if (!r.plot) continue;
     for (int s = 0; s < kSlotsPerRow; ++s) {
+      // A persistence layer is bound to an event series too, and it is the *past*: letting one
+      // widen this window would move the pin -- and with it the framing and the numbers a pinned
+      // measurement reads -- every time an older acquisition happened to be wider than the one on
+      // screen. What is pinned is the current event's window, and only that.
+      if (r.layer[static_cast<std::size_t>(s)] > 0) continue;
       const EventSeries* ev = r.slots[static_cast<std::size_t>(s)].bound_event();
       if (ev == nullptr || ev->size() < 2) continue;
       const plot::Range b = ev->x_bounds();
@@ -857,7 +1252,7 @@ void RowSet::fit_x() {
   // *members* have to be written as well as the group, because `hold_pinned_window()` prefers a
   // member that has moved since our own last statement -- that is how it tells a gesture from its
   // own echo -- so writing the group alone would be reverted to the zoomed-in member next frame.
-  const plot::Range pin{-pinned_pre_, pinned_post_};
+  const plot::Range pin = pinned_range();
   if (!(pin.span() > 0.0) || !std::isfinite(pin.min) || !std::isfinite(pin.max)) return;
   for (int i = 0; i < rows_; ++i) {
     Row& r = row(i);
@@ -884,6 +1279,18 @@ void RowSet::sync_cursors(int drag_row) {
     const double yb = r.plot->cursor(r.ruler_b).y;
     if (y > kParked * 0.5) r.ruler_y = y;
     if (yb > kParked * 0.5) r.ruler_b_y = yb;
+    // The row's cells share one y axis, so the dragged ruler is the row's: every other cell of the
+    // figure row takes the values and draws them (`Free`: the dragged cell's own value just came
+    // out of its plot and must not be snapped).
+    const int fr = figure_row_of(drag_row);
+    const int first = first_plot_of_row(fr);
+    for (int i = first; i < first + cells_in_row(fr); ++i) {
+      if (i == drag_row) continue;
+      Row& mate = row(i);
+      mate.ruler_y = r.ruler_y;
+      mate.ruler_b_y = r.ruler_b_y;
+      place_cursors(mate, plot::CursorPlacement::Free);
+    }
   }
   bool push = false;
   if (cursor_mode_ != CursorMode::Horizontal) {

src/plot_host.hpp

@@ -112,6 +112,16 @@ class RowSet {
     /// `add_trace()`, which is why this is stored rather than resolved per frame --
     /// changing it needs a rebuild, and `assign()` already forces one.
     std::array<int, kSlotsPerRow> color_index = {0, 1, 2, 3};
+    /// The *persistence layer* this slot draws: 0 for a signal's own trace (whatever the frame's
+    /// display mode binds it to), `a` > 0 for the acquisition `a` latches back, drawn at
+    /// `slot_alpha`. A layer slot holds a suffixed name (`sine (A)`) and no channel at all -- it is
+    /// not a signal, and `channel[]` stays -1 for it (see `assign_layer()`).
+    std::array<int, kSlotsPerRow> layer = {0, 0, 0, 0};
+    /// How bright the slot's trace is built: 1 for a signal's own trace, `persist_alpha(layer)` for
+    /// a persistence layer, multiplied into `trace_alpha_`. It lives on the slot because a `Plot`
+    /// fixes a trace's colour -- alpha included -- at `add_trace()`, so a per-layer brightness is a
+    /// property of the trace's *creation*, which is what a rebuild is for.
+    std::array<float, kSlotsPerRow> slot_alpha = {1.0f, 1.0f, 1.0f, 1.0f};
     plot::u32 axis_x = 0;
     plot::u32 axis_y = 0;
     plot::u32 cursor_a = 0;
@@ -145,8 +155,43 @@ class RowSet {
     double ruler_b_y = 0.0;
   };
 
+  /// The number of **plots** (cells over all figure rows), which is what `row(i)` indexes. With no
+  /// row split it is also the number of figure rows; `figure_row_count()` is the latter.
   int row_count() const noexcept { return rows_; }
 
+  /// A figure row holds one to `kMaxCellsPerRow` plots side by side, sharing the row's height and
+  /// the figure's one x window. The flattened plot index (`row(i)`, `Row::plot`, the figure's
+  /// `plot(i)`) runs row-major: row 0's cells left to right, then row 1's.
+  static constexpr int kMaxCellsPerRow = 4;
+  int figure_row_count() const noexcept { return static_cast<int>(cells_per_row_.size()); }
+  /// How many cells figure row `fr` holds; 0 for a row that does not exist.
+  int cells_in_row(int fr) const;
+  /// The flattened index of figure row `fr`'s first cell; `row_count()` for `fr ==
+  /// figure_row_count()`.
+  int first_plot_of_row(int fr) const;
+  /// The figure row plot `plot` is in, or -1 for an index that is not a plot.
+  int figure_row_of(int plot) const;
+  /// Plot `plot`'s 0-based position inside its row, or -1.
+  int cell_of(int plot) const;
+  /// Figure row `fr`'s cell width shares (empty means equal; always empty for a single-cell row).
+  const std::vector<float>& cell_weights(int fr) const;
+  /// What the UI calls a plot: the figure row's number (`"2"`) for a single-cell row, the number
+  /// and a letter (`"2a"`..`"2d"`) for a split one.
+  std::string plot_label(int plot) const;
+
+  /// Adds an empty cell to figure row `fr` at position `at` (clamped to the row), pushing the
+  /// cells at and after it right. False at `kMaxCellsPerRow` cells or `kMaxRows` plots.
+  bool insert_cell(int fr, int at);
+  /// Removes plot `plot`. A single-cell row removes the row itself (`remove_row()`); false when
+  /// that would leave no plot.
+  bool remove_cell(int plot);
+  /// Figure row `fr`'s cell width shares, normalised by the plotter; empty means equal.
+  void set_cell_weights(int fr, std::vector<float> w);
+  /// Replaces the whole arrangement: `cells[r]` plots in figure row `r`, each clamped to
+  /// `1..kMaxCellsPerRow` and the total to `kMaxRows`. Weights are reset; plot contents stay in
+  /// their flattened slots.
+  void set_cells_per_row(std::vector<int> cells);
+
   /// The alpha every trace is drawn with. The *group* views use it: accumulating events wants their
   /// traces translucent so that agreement between them reads as brightness, which is the whole point
   /// of a persistence display. It is mixed into the palette colour where the trace is created, so it
@@ -159,22 +204,24 @@ class RowSet {
   /// trace set or the row count changes, so weights that lived only in the figure would be lost on the
   /// first drop or row change after a user had sized their layout.
   void set_row_weights(std::vector<float> weights);
-  /// Sizes the stored weights to the rows that exist and hands them to the figure.
+  /// Sizes the stored weights to the figure rows that exist and hands them to the figure. Weights
+  /// are per **figure row**, not per plot.
   void apply_row_weights();
   const std::vector<float>& row_weights() const noexcept { return row_weights_; }
-  /// Shows `rows` rows. A changed count rebuilds the figure, since a `Figure`'s row
-  /// count is fixed at construction.
+  /// Shows `rows` figure rows of one cell each (so `rows` plots, any split undone). A changed
+  /// arrangement rebuilds the figure, since a `Figure`'s shape is fixed at construction.
   void set_row_count(int rows);
-  /// Inserts an empty row at `at` (0 = above the first row, `row_count()` = below the
-  /// last), pushing the rows at and below it down. Returns false at `kMaxRows`.
+  /// Inserts an empty single-cell figure row at `at` (0 = above the first row,
+  /// `figure_row_count()` = below the last), pushing the rows at and below it down with their
+  /// cells. Returns false at `kMaxRows` plots.
   ///
   /// The rows below move as *rows*: their trace assignments, colours and cursors follow
   /// them, so inserting above row 1 does not renumber what row 1 was plotting. The
   /// figure's `Plot`s are not what moves -- they are rebuilt and re-dealt -- which is
   /// the same mechanism a row-count change already used.
   bool insert_row(int at);
-  /// Removes row `at` and pulls the rows below it up. Returns false when only one row
-  /// is left: a figure with no rows has nothing to draw and no way back.
+  /// Removes figure row `at` (with all its cells) and pulls the rows below it up. Returns false
+  /// when only one row is left: a figure with no rows has nothing to draw and no way back.
   bool remove_row(int at);
   Row& row(int i) { return storage_[static_cast<std::size_t>(i)]; }
   const Row& row(int i) const { return storage_[static_cast<std::size_t>(i)]; }
@@ -200,6 +247,42 @@ class RowSet {
   /// The channel index a row/slot holds, or -1.
   int channel_of(int row, int slot) const;
 
+  // --- persistence layers ---------------------------------------------------
+  /// The brightness a persistence layer is drawn at, `a` acquisitions back: the acquisition on
+  /// screen is the full-bright one and each older one is **half** the previous, so the schedule is
+  /// exponential in age -- 1, 0.5, 0.25, 0.125, ... and by the seventh (0.008, `kMaxPersistDepth`)
+  /// the layer is gone. Halving is per acquisition and not per *depth*, so changing N re-cuts how
+  /// many are kept without rescaling the ones already on screen.
+  static float persist_alpha(int age) noexcept;
+
+  /// Binds a row's slot to a persistence *layer*: the acquisition `age` latches back, at `alpha`
+  /// (see `Row::layer`). The name carries the layer's suffix (`sine (A)`, `sine #4`), which is what
+  /// keeps a layer out of the signal list and out of the measurements -- it is not a signal -- while
+  /// `signal_color()` still resolves it to the base signal's own colour.
+  void assign_layer(int row, int slot, std::string signal_name, std::string display_name,
+                    int color_index, int age, float alpha);
+  /// Frees every slot bound to a layer. What turning persistence off -- or the trigger -- is.
+  void clear_layers();
+  /// Lays the persistence layers out over the rows' free slots, one per (signal, age): the signal's
+  /// own trace stays where it is and its layers take the free slots of the *same* row, layer by
+  /// layer (age 1 for every signal first, then age 2, as the accumulate path does), so a row that
+  /// runs out of room draws as many layers as it has room for and no more. Every slot the plan does
+  /// not fill is freed, which is what makes the display follow a layout change, a depth change and a
+  /// signal's removal without any caller having to reset anything.
+  ///
+  /// Returns the number of layers placed; `want` is how many the depth asked for, so a caller can
+  /// say when a layout could not show them all.
+  int sync_layers(int depth, int* want);
+  /// The layer a slot is drawing, 0 for a signal's own trace.
+  int layer_of(int row, int slot) const;
+  /// The slot's own brightness (1 unless it is a layer).
+  float slot_alpha_of(int row, int slot) const;
+  /// How many slots are layers, over every row: the reading that says the layers exist.
+  int layer_slots() const;
+  /// The layers of one row, oldest first, as `(age, alpha)` pairs -- the ordering a reader has to
+  /// see to know the decay is the right way round.
+  std::vector<std::pair<int, float>> row_layers(int row) const;
+
   /// Rebinds every slot to what `mode` says it should show this frame. Called every
   /// frame, because the channel list is renumbered by any structural change.
   ///
@@ -385,6 +468,12 @@ class RowSet {
   /// Whether a window is pinned: a held event, a filling capture or a paused view. The condition
   /// `fit_x()` branches on, which is why the fit probe reports it.
   bool window_pinned() const noexcept { return pinned_; }
+
+  /// The pin's own extent, in the x the rows' axes read -- what a pinned view is a view *of*.
+  /// The one expression of it, shared by the framing (`hold_pinned_window()`, `fit_x()`) and by
+  /// the measurement pane, which measures *this* while the view is pinned so that a gesture
+  /// changes no number (see `update_measures()`); meaningless when `window_pinned()` is false.
+  plot::Range pinned_range() const noexcept { return {-pinned_pre_, pinned_post_}; }
   /// True when the pin already *is* this window. A caller that re-states a pin every frame -- the file
   /// view does, from the ring's own extent -- uses this to update the pin's numbers with
   /// `set_data_pin()` instead of writing the group's range again with `pin_event_window()`, which would
@@ -511,9 +600,15 @@ class RowSet {
   std::unique_ptr<plot::Figure> figure_;
   /// The one x link group every visible row belongs to. Groups are numbered from 1.
   plot::u32 x_group_ = 0;
+  /// The number of plots; `sum(cells_per_row_) == rows_` always.
   int rows_ = 1;
+  /// Cells per figure row, and each row's cell width shares (empty = equal; kept empty for a
+  /// single-cell row). Both are state of the `RowSet`, restated to every new figure.
+  std::vector<int> cells_per_row_{1};
+  std::vector<std::vector<float>> cell_weights_ = std::vector<std::vector<float>>(1);
+  void apply_cell_weights();
   float trace_alpha_ = 1.0f;
-  std::vector<float> row_weights_;
+  std::vector<float> row_weights_;  ///< per figure row
   double window_s_ = 2.0;
   double trigger_marker_x_ = 0.0;
   bool trigger_marker_on_ = false;

src/settings.cpp

@@ -3,6 +3,7 @@
 
 #include "settings.hpp"
 
+#include <algorithm>
 #include <cstdlib>
 #include <cstring>
 #include <fstream>
@@ -64,8 +65,15 @@ Settings load_settings() {
       s.event_cache_max = std::max(0, std::atoi(value.c_str()));
     } else if (key == "relative_time") {
       s.relative_time = parse_bool(value, s.relative_time);
+    } else if (key == "memory_limit_mb") {
+      const long mb = std::strtol(value.c_str(), nullptr, 10);
+      if (mb >= 16) s.memory_limit_mb = static_cast<int>(std::min<long>(mb, 1000000000L));
     } else if (key == "theme") {
       if (value == "auto" || value == "light" || value == "dark") s.theme = value;
+    } else if (key == "contextual_help") {
+      s.contextual_help = parse_bool(value, s.contextual_help);
+    } else if (key == "tour_seen") {
+      s.tour_seen = parse_bool(value, s.tour_seen);
     }
   }
   return s;
@@ -79,7 +87,14 @@ bool save_settings(const Settings& settings) {
   out << "event_cache_dir = \"" << settings.event_cache_dir << "\"\n";
   out << "event_cache_max = " << settings.event_cache_max << "\n";
   out << "relative_time = " << (settings.relative_time ? "true" : "false") << "\n";
+  out << "memory_limit_mb = " << settings.memory_limit_mb << "\n";
   out << "theme = \"" << settings.theme << "\"\n";
+  // The two help keys are the *app's* memory rather than the dialog's: the contextual-help rows --
+  // the Help menu's and the source chooser's own -- write the first, and the first-run tour writes the
+  // second. `read_rows()` in the preferences starts from `load_settings()`, so a dialog save carries
+  // them through untouched.
+  out << "contextual_help = " << (settings.contextual_help ? "true" : "false") << "\n";
+  out << "tour_seen = " << (settings.tour_seen ? "true" : "false") << "\n";
   out.flush();
   return out.good();
 }

src/settings.hpp

@@ -30,9 +30,24 @@ struct Settings {
   /// buffers are planned before any stream is known, so it takes effect on the next start (the
   /// preferences dialog says so, like the configurations dialog does).
   bool relative_time = false;
+  /// The hard ceiling on the sample rings' memory, in MiB, for the whole application rather than per
+  /// source (`--memory-limit-mb` overrides it for one run). The planner halves a source's sample
+  /// budget until the rings fit under it. Unlike the cache directory and relative time it applies as
+  /// it is changed: a running scope re-plans its buffer (and so drops its history) when the new limit
+  /// changes the rings.
+  int memory_limit_mb = 8192;
   /// "auto", "light" or "dark": what the interface should look like. Kept as the three names libadwaita
   /// uses, so the file says what the setting is rather than what an enum happens to be numbered.
   std::string theme = "auto";
+  /// The contextual-help layer: a small "?" beside each surface it can explain. **Off by default** --
+  /// a first run shows the interface as a user expects it and the layer is asked for, from the Help
+  /// menu or from the chooser's own help menu, by whoever wants it; on is then a decision that
+  /// survives a restart.
+  bool contextual_help = false;
+  /// Whether the guided tour has been offered. A first run has no file carrying this key, so the tour
+  /// starts itself once; the flag is written when it *starts*, not when it finishes, because a user who
+  /// skips it has still seen it and a second launch with the same tour would be a nuisance.
+  bool tour_seen = false;
 };
 
 /// The defaults, as a value rather than as a comment: what the dialog's *Defaults* button writes and