ui: the sidebar's tabs become one dock; Measure and Signals by keyboard section; session keeps the dock's state

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

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

@@ -50,7 +50,7 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   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, Configurations) and the one editor that is not a pane (the layout editor): the signal list
-  is a *tab* of the sidebar, so there is nothing left to reveal or hide about it. The Arm/Disarm button in the trigger panel still has text.
+  is a section of the sidebar's dock, so there is nothing left to reveal or hide about it. The Arm/Disarm button in the trigger panel still has text.
 - **Five 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
@@ -61,9 +61,9 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   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.
 
-  The sidebar's **tabs have no icons any more**: two glyphs (`udpscope-tab-measure-symbolic`,
+  The sidebar has **no tabs any more** (it is one dock): two tab glyphs (`udpscope-tab-measure-symbolic`,
   `udpscope-tab-signals-symbolic`, each a 32x16 pair) were drawn for them and judged not understandable
-  enough, so the tabs are text and both SVGs were deleted. The *trigger's* own icon was redrawn to the
+  enough, so the tabs were text, and both SVGs were deleted. The *trigger's* own icon was redrawn to the
   Signals glyph's picture at that time and kept it.
 - **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
@@ -229,11 +229,13 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   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 a tab stack now, and has no `GtkRevealer` left in it**: an `AdwViewSwitcher`
-  above an `AdwViewStack`, each page a `GtkScrolledWindow` of its own (the two pages are different
-  heights, so one shared scroller would leave a switch scrolled where the new page never asked to
-  be). The reason is the one this trap teaches: five sections competing for one 320 px column left
-  every one of them short of room. A *feature's* on/off is no longer a visibility at all -- the
+  **The sidebar is one dock now, and has no `GtkRevealer` left in it**: a single `GtkScrolledWindow`
+  (`dock_scroller`) holding the signal list, the cursors and the measurements one under another. 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: sections competing for one 320 px column each left every one of them short of room, and
+  a scroller gives each its natural height. `m` and `g` scroll the dock to the cursors and to the signal list
+  (`dock_show_section()`). A *feature's* on/off is no longer a visibility at all -- the
   **cursors'** toggle sets its pane's **body** insensitive -- 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
@@ -241,23 +243,15 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   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 stack's hidden page measures 0x0 too and is still
-  given the leftover width, so **ask about state, not about size** carries over unchanged. Every
-  allocation read in the sidebar is a debug capture, and each reads 0 on the page that is *not*
-  current -- a change in what the reading means, not a defect, and no functional code may depend on
-  those numbers.
-- **The sidebar's tabs are text: `AdwViewSwitcherPolicy.wide`, a title on every page, no icon.** The
-  built-in pages get their titles in the `.ui` and a source kind's pages from `SourcePanel::title`
-  (`adw_view_stack_add_titled`); the page's *name* still identifies it to `select_side_tab()` and the
-  session file. An icon-only version existed (policy `narrow`, empty titles, the pills named in code by
-  `name_side_tabs()`, because `narrow` still draws a label beside an icon); it was reversed because the
-  glyphs were not understandable. A page added with an empty title is a blank pill, and
-  `switcher: … pills=N labels=N images=0 pages=N` reads it as `labels` below `pills`. **No icon at all**
-  is not what "no `icon-name`" gives you: `AdwViewSwitcherButton` always builds a `GtkImage` and falls
-  back to `image-missing` (the `[x]` placeholder, which also squeezed the title to "Meas..."), and no
-  property turns it off. `keep_tabs_icon_free()` (`src/ui_source.cpp`) hides every image in the switcher,
-  re-hides one that is shown again, and re-runs on the stack's `items-changed` (connected *after* the
-  switcher's own, so the new button exists) and on the switcher's `map`; `images=0` is the reading.
+  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 wish is persisted (`dock = true|false` in the session file) and a change of it
+  schedules a save. There is no tab icon to keep clear any more: the `keep_tabs_icon_free()` workaround for
+  `AdwViewSwitcherButton`'s placeholder `[x]` image went with the switcher, and `dock:` in the dump
+  replaces the `switcher:` line.
 - **An *overlaid* sidebar covers the plot, so a drag out of it has nowhere to land.** `collapsed` in an
   `AdwOverlaySplitView` means the sidebar sits *on* the plot rather than beside it: the pointer is over the
   list, never over a drop target, and a signal can be dragged but not dropped. `row_drag_sidebar()` hides
@@ -278,7 +272,7 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   `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 switcher must
+  (`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.