re: a second JP capture closes the transfer -- and corrects my own noise claim

Last turn I transferred the EN title's capture noise to the JP box and flagged
the gap: build 7 carries ptloop01/02.rat which may animate inside that region
where the EN plate does not, and the era adjudication rests on a single capture.
Took a second, independent capture from a fresh boot in a separate session
(jp_title_session.sh -- sets ja, captures, always restores en; verified back at
language=1).

Within-run stability reproduces: 0 of 138 600 px in the ROI across four
comparisons, with 47k-73k px moving whole-frame as the contrast control.

BETWEEN SESSIONS, inside the box the adjudication uses: 645 of 164 124 px
differ, RMSE 0.3215, against 116 492 px whole-frame -- genuinely different
sessions. And the verdict reproduces to three decimals: stale 58.412 -> 58.413,
fixed 41.690 -> 41.692, margin 16.722 -> 16.721.

The shape is the useful part: capture noise moves both candidates together, so it
nearly cancels in a MARGIN. Absolute scores moved 0.001-0.002 while the margin
moved 0.001 against an in-box noise of 0.32. A margin between two renders scored
on one capture is far more robust than either score is.

CORRECTION to a claim I made earlier today and sent to the port: I said the
settle-vs-rest negative was STRENGTHENED because 1.48 sits below the whole-frame
capture spread of 2.8. Wrong comparison -- the measurement lives in the box, and
in-box between-session noise is 0.32, so 1.48 is well above it. The negative
rests on the render axis alone (1.2, ratio 1.2x), exactly as first stated. I
reached for a number that was to hand rather than the one that applies, which is
the same family as the errors we have both been cataloguing.

METHOD gains: match the noise floor to the quantity, including which noise
applies; and sylpheed-port's point that an instrument which rounds away the thing
being verified cannot verify it (they called a harness reproducible from an RMSE
printed to two decimals when the residual was 0.0565).

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

docs/re/METHOD.md

@@ -331,6 +331,20 @@ agent's loop prompt, i.e. nowhere durable. See [`README.md`](README.md) for the
   noticing that what you are about to look at merely *correlates* with what you
   want to know.
 
+* **Match the noise floor to the quantity — including which noise actually
+  applies.** A margin needs a floor, but the floor must be the one that moves
+  *that* margin. Two renders scored against one capture share the capture, so
+  capture noise largely **cancels**: measured on the JP title, the absolute scores
+  moved 0.001–0.002 between sessions while the **margin** moved 0.001, against an
+  in-box capture noise of 0.32. Judging that margin against a whole-frame capture
+  spread — a number that was simply to hand — made a non-decisive result look
+  decisive, and this corpus published that for part of a day.
+  ⚠️ Relatedly, `sylpheed-port` verified a harness "reproducible" from an RMSE
+  **printed to two decimals** when the residual was 0.0565: **an instrument that
+  rounds away the thing being verified cannot verify it.** Check the printed
+  precision against the quantity before quoting the number, and prefer comparing
+  *frames* to comparing a statistic about them.
+
 ## Runtime / emulator
 
 * **Look at the PNG** — and check its dimensions.