re: an uncontrolled capture instant, and why the ptlogo_eff3 result survives it

sylpheed-port's harness grabbed main_menu at t=9.00 in one session and t=8.00 in
the next. One keyframe unit apart, mid-build-in, is 70 % of the picture, and it
read as "the change broke two screens" -- a real measurement of the wrong thing.
The instant was stable WITHIN a session and drifted BETWEEN them, so every cheap
reproducibility check said deterministic. Their flags are their harness's, not
sylpheed-cli's (checked: `screen` has only list/info/render), so the tool defect
is not in my crate -- but the hazard generalises to every live capture here.

It would void this iteration's ptlogo_eff3 adjudication if the JP capture had
been taken at an arbitrary moment. It was not, and for two independent reasons
recorded rather than assumed: the grab was gated on the plate pulse, the title's
own settled signature, with the gate and a contrast control written beside the
capture in jp-title-at-rest.txt; and the --at sweep shows the capture on a
plateau flat to 1.2 RMSE across 105 units against edges at 78, where a capture
caught mid-build would give a sharp minimum. The sweep was run for a noise scale
and answers this too -- which is luck, so METHOD now names both defences.

METHOD: pin a capture's instant explicitly, and do not infer stability from
repeat runs inside one session. Gate the grab on a settled signal prospectively,
and sweep --at retrospectively -- a broad flat minimum with sharp edges means at
rest, a sharp minimum means the instant is load-bearing.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Wuu56cE8vJGTBtn1ppsk8v

docs/re/METHOD.md

@@ -263,6 +263,27 @@ agent's loop prompt, i.e. nowhere durable. See [`README.md`](README.md) for the
   the era control re-run live — it holds. The audit was cheap; not doing it would
   have left a measurement resting on an assumption about a filesystem.)
 
+* **A capture taken at an uncontrolled instant is a real measurement of the wrong
+  thing** — and the cheap check for it passes. `sylpheed-port`'s harness grabbed
+  `main_menu` at t=9.00 in one session and t=8.00 in the next; one keyframe unit
+  apart, mid-build-in, is **70 % of the picture**, and it read as "the change broke
+  two screens". ⚠️ The instant was **stable within a session and drifted between
+  them**, which is the worst form: three consecutive runs are byte-identical, so
+  every cheap reproducibility check says "deterministic". Pin the instant
+  explicitly; do not infer stability from repeat runs inside one session.
+
+  **Two defences, and a live capture wants both.** *Prospectively*, gate the grab
+  on a signal that the screen has settled — the title's plate pulse, say — and
+  record the gate beside the capture. *Retrospectively*, sweep the screen's own
+  timeline with `screen render --at` and score the capture against each instant: if
+  it lies on a **broad flat minimum with sharp edges**, it was at rest; a sharp
+  minimum means it was caught mid-build and the instant is load-bearing. The
+  `ptlogo_eff3` adjudication in [`ui-resting-pose.md`](structures/ui-resting-pose.md)
+  happens to have both — the capture was gated on the plate pulse, and the `--at`
+  sweep (run for a noise scale, not for this) shows a plateau flat to 1.2 RMSE
+  across 105 units against edges at 78. The sweep was luck; the entry is here so
+  the next one is not.
+
 ## Runtime / emulator
 
 * **Look at the PNG** — and check its dimensions.

docs/re/structures/ui-resting-pose.md

@@ -54,6 +54,22 @@ and cannot separate the *policies*, and the number that says so is the plateau's
 own width. The settle-instant proposal stays unadopted on the same evidence it
 had.
 
+### ✅ Why the capture's own instant is not a confound here
+
+`sylpheed-port` found their harness capturing the same screen one keyframe unit
+apart in different sessions — 70 % of the picture, mid-build-in, and stable enough
+within a session that repeat runs said "deterministic". That hazard would void this
+adjudication if the JP capture had been grabbed at an arbitrary moment. It was not,
+and there are two independent reasons:
+
+* **prospective** — the grab was gated on the **plate pulse**, the title's own
+  settled signature, and [`data/jp-title-at-rest.txt`](../data/jp-title-at-rest.txt)
+  records the gate and a contrast control taken with it;
+* **retrospective** — the `--at` sweep above shows the capture on a **plateau flat
+  to 1.2 RMSE across 105 units with edges at 78**. A capture caught mid-build would
+  produce a sharp minimum instead. The sweep was run for a noise scale and answers
+  this too.
+
 ⚠️ **Reach.** One screen, one capture. The absolute residual is ~40 RMSE even at
 the best instant, because the JP title carries live animation a static render
 cannot reproduce; every comparison here is relative and none of it says our render