docs: the readouts strip hides when empty

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

docs/claude/architecture.md

@@ -137,9 +137,13 @@ touching the data path.
   **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()` -- 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). The tick
+  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

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

@@ -148,20 +148,25 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   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 whenever the dock is not beside the plot.**
+- **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`
+  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 only 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; in a collapsed window the dock is an overlay on the plot and the strip
+  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, and `visible_ok=1` that `visible` equals `expected`.
+  `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.

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

@@ -66,8 +66,12 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   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 and never hidden -- through `dock_set_cursors_sensitive()`, which writes the dock's grid and 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

docs/claude/probe-readings.md

@@ -1845,16 +1845,20 @@ These ride on the `[cursors-probe]` readings (every state line gets a `dock curs
 ## `strip:` (the readouts strip)
 
 ```
-[cursors-probe]  <what> strip: visible=1 expected=1 visible_ok=1 dock_shown=1 cursors=4 measures=0 same_text=1 h=26 sens_same=1 collapsed=1 window=756
-[measures-probe] <what> strip: visible=1 expected=1 visible_ok=1 dock_shown=1 cursors=0 measures=12 same_text=1 h=26 sens_same=1 collapsed=1 window=756
+[cursors-probe]  <what> strip: visible=1 expected=1 visible_ok=1 dock_shown=1 cursors=4 measures=0 same_text=1 h=26 sens_same=1 collapsed=1 window=756 groups=100 groups_ok=1
+[measures-probe] <what> strip: visible=1 expected=1 visible_ok=1 dock_shown=1 cursors=0 measures=12 same_text=1 h=26 sens_same=1 collapsed=1 window=756 groups=010 groups_ok=1
+[measures-probe] start strip: visible=0 expected=0 visible_ok=1 dock_shown=1 cursors=0 measures=0 same_text=1 h=0 sens_same=1 collapsed=1 window=756 groups=000 groups_ok=1
 [cursors-probe]  dock hidden strip: visible=1 expected=1 visible_ok=1 dock_shown=0 cursors=4 measures=0 same_text=1 h=26 sens_same=1 ...
 [cursors-probe]  dock restored strip: visible=1 expected=1 visible_ok=1 dock_shown=1 ... collapsed=1 window=756
 ```
 
 One `strip:` line follows every `dock cursors:` / `dock measures:` line, and each probe ends with a drive that puts the dock away through the wish (`sidebar_wanted = false`), reads the strip 600 ms later (`dock hidden`), restores the wish and reads again (`dock restored`).
 
-- **`visible` equals `expected`, and `expected = !dock_shown || collapsed`** (`dock_shown` is `show-sidebar`, `collapsed` the split view's, both read in the same frame as `visible`). `visible_ok=1` is that equality; `visible_ok=0` is `sync_readouts_strip()` not run, or run before the reconciliation. A single such line right after the probe's own `update_side_visibility()` or on the very first line (the tick has not set `collapsed` yet) is the sub-frame before the next tick and not a defect.
-- **`visible=1 expected=1` on every line under `xvfb-run`**, the `dock restored` line and the lines with `dock_shown=1` included: the window is 756 px, below the 900 px `kSidebarRoom`, so the split view is collapsed, the dock is an overlay on the plot, and the strip stays. `visible=0` there is the old rule (hidden whenever the dock is shown) or `collapsed` not being read. The wide case (`collapsed=0`, `dock_shown=1`, `visible=0 expected=0`) is **not reachable from a probe**, because a window with no manager cannot be resized by `gtk_window_set_default_size()`.
+- **`visible` equals `expected`, and `expected = (!dock_shown || collapsed) && (cursors on || measures non-empty)`** (`dock_shown` is `show-sidebar`, `collapsed` the split view's, both read in the same frame as `visible`; "cursors on" is the cursors toggle, not the `cursors=` chip count, which is a rebuild's and is 1 even with them off). `visible_ok=1` is that equality; `visible_ok=0` is `sync_readouts_strip()` not run, or run before the reconciliation. A single such line right after the probe's own `update_side_visibility()` or on the very first line (the tick has not set `collapsed` yet) is the sub-frame before the next tick and not a defect.
+- **What each leg reads.** `[measures-probe] start` (before the probe adds anything, from a **fresh** config: a stored session brings its measurements back) is the "neither" state: `visible=0 expected=0 groups=000 h=0`. The measures probe's later lines have measurements and the cursors off: `groups=010`. The cursors probe alone has the cursors on and no measurements: `groups=100`; run after the measures probe in the same session it has both: `groups=111`. A line with the strip visible and `groups=000`, or hidden with a group on, is `sync_readouts_strip()` not called from that path.
+- **`groups=<cursors><measures><separator>`** is which of `strip_cursor_group`, `strip_measure_group` and `strip_sep` are visible; **`groups_ok=1`** is that they equal (cursors on, a measurement, both). `0` is a group left over from the previous state.
+- **`h=0` with `visible=1` on the `cursors-probe ... on` and `measures-probe ... added` lines** is the strip shown in the same frame the probe reads it, before its first allocation; the next line reads 26. It is not a `visible_ok` miss: the toggle handler and `rebuild_measures_pane()` call `sync_readouts_strip()` themselves, so `visible` is already right.
+- **`visible=1 expected=1` on every line that has something to read, under `xvfb-run`**, the `dock restored` line and the lines with `dock_shown=1` included: the window is 756 px, below the 900 px `kSidebarRoom`, so the split view is collapsed, the dock is an overlay on the plot, and the strip stays. `visible=0` there is the old rule (hidden whenever the dock is shown) or `collapsed` not being read. The wide case (`collapsed=0`, `dock_shown=1`, `visible=0 expected=0`) is **not reachable from a probe**, because a window with no manager cannot be resized by `gtk_window_set_default_size()`.
 - **`h` is 26 with `visible=1`, 0 with `visible=0`.** Any other visible height is the chips setting the strip's height (the button trim in `ui_widgets.cpp` or the `height-request` lost).
 - **`same_text=1` is the assertion**: every strip label (the cursors' `who` and delta, the measurements' values) has the dock's text, and the counts of chips match the dock's lines. `0` is a value written to one view only -- a dock cell set without `dock_cursor_cell()` / `dock_measure_value()`, or a rebuild that did not mirror.
 - **`cursors` / `measures`** are the chip counts and equal the dock's `lines`.

docs/claude/verification.md

@@ -438,9 +438,9 @@ precedent, not an exception.
 - `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`; `expected=` is that, `visible_ok=1` that the strip agrees); each probe
+  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). **`same_text=1` on every one** is the assertion that 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.