added status line info:

CLAUDE.md

@@ -120,6 +120,13 @@ Two lines of the self-check output are assertions in disguise:
   `64·⌈(10+len(header)+1)/64⌉ + rows·(16 + 4·cols)`, so a size that is not that is a
   mispacked record. Read it back with `pd.DataFrame(np.load(path))` after changing
   either writer.
+- `badge frames: lit=L dim=D idle=I` — the activity badge's phase per frame. Over a run
+  that acquired anything **both `lit` and `dim` must be non-zero**: that is what "it
+  blinks" means, and a badge stuck lit is indistinguishable from a working one in a
+  screenshot. One or two `idle` frames at the start are the frames before the socket
+  connected; a large `idle` is correct only when the run paused or disarmed (a
+  `UDPSCOPE_PROBE_DISARM_MS` run should show hundreds). The `mode ...` lines carry the
+  rest of the status line, so `rate` and `last event ... ago` are checked there.
 
 The probes are the regression net — when changing UI or plot-host behaviour, extend
 the probe/dump in `src/ui.cpp` rather than adding a separate harness.
@@ -233,6 +240,11 @@ far the largest file.
 - **Layout must not depend on content.** The y gutter is reserved at the widest label
   `TickFormat::Si` can produce and only ever grows; the status label is ellipsized so
   its text cannot drive the paned divider. Both exist to stop per-frame relayout.
+  The same rule is why the activity badge is one glyph in three colours rather than
+  three glyphs, why the `rate` field collapses to one figure or a range instead of a
+  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.
   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
@@ -271,6 +283,11 @@ far the largest file.
 - **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 status line's per-second fields are measured once a second, not per frame.**
+  `App::stored_rate`/`declared_rate` and the label's tooltip are refreshed on the same
+  tick as the channel dump; the status line only formats what is already there. The
+  badge's markup is likewise rewritten on a change of phase (twice a second), never on
+  all sixty frames.
 - **The header bar's buttons are icon-only**, so headless probes must reach them
   through the `App` pointers (`trigger_toggle`, `pause_button`, …), not via
   `find_labelled_button()`. The Arm/Disarm button in the trigger panel still has text.