improved perfs and event management

docs/claude/invariants-time-axis-and-window.md

@@ -31,6 +31,21 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   reasons (an event pin) call `sync_window_display()` alone, which only restates the control and
   never moves the plot — calling `apply_time_window()` there would clamp a legitimately short
   capture up to the requested window.
+- **With nothing bound, `set_time_window()` frames `{-window, 0}` and never `{0, window}`.** Under
+  a following x group a range states two things — its span, and *through its maximum* where the
+  window sits behind the live edge — so a maximum **at** the edge is what makes the offset zero.
+  When there is a live edge to read that is `{newest - window, newest}`; when there is not, the
+  edge the live view would put at x = 0 is 0, so the equivalent statement is `{-window, 0}`.
+  Asking for `{0, window}` there is an offset of a *whole window*. This is not a rare fallback:
+  "no samples bound" is the state every structural change leaves behind, and
+  `apply_time_window()` re-plans the rings and *then* calls this, so it is the axis a mode change
+  is drawn with until the first sample lands. With `{0, window}` the two or three frames after
+  every event or waveform open drew the time base one screen to the left of where the following
+  frames drew it — a trace that jumps a screen sideways and comes back, which is what "opening
+  events or even waveform sometime result in data flickering (like time base) and is unusable"
+  was. The reading is the dump's traceless paint counts: `mode=live` 38 → 0 and `mode=waiting`
+  2 → 40, the latter being the point — a waiting view now paints its empty axis in the *same*
+  place every frame instead of twitching into a framed one.
 - **The x labels go relative on the tick *step against the label resolution at the axis'
   magnitude*, never on the span.** `RowSet::update_time_labels()`'s question is only ever "can
   this step be written at this magnitude": `TickFormat::Time` carries three significant figures