docs: the readouts dock, the cursors and measurement pages

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

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

@@ -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
@@ -29,7 +29,7 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   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
@@ -130,9 +130,16 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   `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** (`side_column` `width-request` 300, the split view's 320 px floor
-  and cap), and it holds one scroller with the cursors and the measurements. A
-  section's visibility is never what makes the dock taller; the scroller is what absorbs the extra.
+- **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, 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=`.
 - **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.