docs: the three new features are described where each of their readers looks

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

README.md

@@ -343,6 +343,26 @@ array of per-node structs was measured and bought **nothing** — at six nodes t
 L1-resident either way. It was kept because a node's state belonging on one cache line is the
 right shape for a graph that grows, not because it showed up.
 
+### Statistics
+
+**Statistics** under the measurements list adds a second line to every measurement: `n`, the
+mean, the standard deviation, and the range. The observations are the pane's own **recomputes**
+— one per refresh, not one per sample — so `n` is a count of *windows measured*, which is what
+makes "the mean frequency over the last four hundred windows" the claim it reads as. The pane
+refreshes at most ten times a second while the window scrolls and exactly once when it settles,
+so a settled window contributes one observation and then stops.
+
+The accumulator is Welford's, not a sum of squares: a measurement whose values sit at 1e9 with
+a spread of 1e-3 is an ordinary case here (an absolute stream time is one), and the naive form
+loses that spread entirely.
+
+**Reset** clears every accumulator. So does editing, adding or deleting a measurement, a CONFIG
+that renames the signals, and a change of the display window — each of those changes *what is
+being measured*, and a mean across the change describes nothing. A pause, a resume, a trigger
+latch, a pan and a zoom do **not** reset: they change which samples are in view, which is
+exactly what a statistic over many windows is meant to average. The toggle itself does not
+reset either, so turning the line off to read the plot and back on again keeps the history.
+
 ## The session layout file
 
 What you arranged is remembered per data source, in
@@ -652,6 +672,47 @@ zooming in past the shift showed nothing at all. The self-check now prints `data
 `drawn=` side by side for the bound trace so the contract is checked rather than
 assumed.
 
+### Qualified trigger conditions
+
+The level-and-edge trigger is one of four shapes the **Shape** dropdown offers, and all four
+are the *same* trigger: the arming, the hold-off, the pre/post event window and the single/auto
+modes are unchanged, and only the question "did an event happen at this sample" differs.
+
+- **edge** — a crossing of the level in the chosen direction. The original behaviour, bit for
+  bit.
+- **pulse width** — a crossing *and* its return, qualified by how long the excursion lasted:
+  `<`, `>`, `within` or `outside` a pair of widths. The event is timed at the **closing** edge,
+  because that is the first sample at which the width is known. `<` a width shorter than the
+  signal's own pulses is the glitch trigger: nothing but a runt satisfies it.
+- **window** — the signal entering or leaving a band between two levels. A band is two levels,
+  so the panel refuses a zero-width one rather than quietly degrading to an edge.
+- **dropout** — the *absence* of a crossing for longer than a timeout. One event per outage:
+  the condition re-arms only when a crossing returns.
+
+A shape's own rows are the only ones shown; the rest are hidden, so the panel never offers a
+width to a window trigger. The condition is **not** persisted in the session file — the session
+has never persisted the trigger — so a restart comes up on an edge trigger.
+
+### Searching the buffer
+
+**Search the buffer**, at the foot of the trigger panel, runs the trigger's *own* condition over
+the whole retained ring and lists every place it holds. There is no second condition editor: a
+second place to spell the same question would be a second place to get it wrong.
+
+The scan runs on the GTK thread in a few milliseconds of work per frame, taking the model's
+mutex for one chunk at a time, so neither the frame rate nor the producer stalls on it. Up to
+10 000 hits are kept; past that the scan stops and says so. If the stream overtakes the oldest
+samples mid-scan the search skips forward to what is still there and reports `the stream
+overtook the oldest samples` rather than returning a hit at a time that no longer exists.
+
+The arrows step through the hits. A step **pauses** the view on the hit, centred, exactly as the
+Pause button does — so the frozen window is pinned and navigable within its own data, and
+resuming returns to the live view. Up to 16 of the hits **in the visible window** are marked on
+every row at once, nearest the centre first and the selected one always among them in its own
+colour; when there are more in view than there are marks the panel says `16 of 38 marks shown —
+zoom in to see the rest`, which is a true statement about the picture rather than a silent
+truncation.
+
 **The live view had two clipping bugs of its own**, both wearing the same face as that
 one: the older part of the trace blank, the newest part fine, and the crosshair still
 reading values in the blank part. Neither is a data bug — the samples were always there.