docs: the readouts dock, the cursors and measurement pages

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

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

@@ -41,6 +41,22 @@ 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.
 - **`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
@@ -55,7 +71,7 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   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* rather than hiding it -- a panel you can still see is a panel you can read, and 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