port: identify their submenu capture as GP_TUTORIAL, using edges where intensity failed

They reached a submenu and could not identify it: intensity correlation cannot
discriminate when the candidates are near-blank, which is what the .tbm hypothesis
predicts. Their capture is 99.999% non-black -- a full-screen background our
renderer omits -- and an additive background swamps intensity but not edges.

Control first: edge correlation against my own title capture over seven GP_TITLE
builds picks build 4 at +0.2792, 1.4x over second and 7.6x over third.

Result: GP_TUTORIAL build 0 at +0.4962, build 1 at +0.3137, best GP_SAVE_LOAD at
+0.0713. Winning r higher than the control's and margin better; both TUTORIAL
builds 4-7x above every SAVE_LOAD build. Independently plausible -- flow.json has
ptbtn03 = TUTORIAL -> TUTORIAL_MENU, not a GP_TITLE build.

The ARCHIVE is identified with a large margin; WHICH BUILD is not -- 1.58x is the
same order as the control's 1.4x and the two are variants of one screen.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N7FiFFFwbvG2uxdcEh8HyF

docs/port/DECISIONS.md

@@ -9,7 +9,7 @@ dies, which is what this file is for.
 
 <!-- INDEX: generated by tools/port/index-decisions -- do not hand-edit -->
 
-142 sections. Search this before re-deriving anything.
+143 sections. Search this before re-deriving anything.
 
 * [P0 — the exporter, 2026-08-28](#p0--the-exporter-2026-08-28)
 * [P1 — Godot draws the screen, 2026-08-28](#p1--godot-draws-the-screen-2026-08-28)
@@ -153,6 +153,7 @@ dies, which is what this file is for.
 * [Applying "grep the corpus for the claim" to my own corpus](#applying-grep-the-corpus-for-the-claim-to-my-own-corpus)
 * [A refuted-claim register, because the audit found what the audit found](#a-refuted-claim-register-because-the-audit-found-what-the-audit-found)
 * [State of the port, and a claim I built on for a week without checking](#state-of-the-port-and-a-claim-i-built-on-for-a-week-without-checking)
+* [Identifying their submenu capture: edges where intensity could not](#identifying-their-submenu-capture-edges-where-intensity-could-not)
 
 <!-- /INDEX -->
 ## P0 — the exporter, 2026-08-28
@@ -8204,3 +8205,61 @@ navigation wrap, the cue bindings, the voice streams and their positional weight
 
 ⚠️ The black hold is measured but sits at **the top of its range** (~6.5–9.2 units,
 authored 9), and that is recorded at the value rather than in a footnote.
+
+## Identifying their submenu capture: edges where intensity could not
+
+They reached and captured a submenu but could not identify it. Their diagnosis is
+the useful part: **correlation cannot discriminate when the candidate renders are
+near-blank**, and near-blank is exactly what the `.tbm` hypothesis predicts — all
+19 `GP_SAVE_LOAD` builds scored −0.004…−0.010, a ranking with no information in
+it. *The instrument is disabled by the thing it was brought in to detect.*
+
+That diagnosis implies its own fix. Their capture is **99.999 % non-black** — a
+full-screen background our renderer omits — and an additive background swamps an
+intensity correlation. **It does not survive an edge map**: a smooth ground has no
+edges, and the UI does.
+
+### The control first, because a ranking is worthless without one
+
+Edge correlation against my own `title` capture, over seven `GP_TITLE` builds
+whose answer I know:
+
+| build | r |
+|---|---|
+| **4 — the right answer** | **+0.2792** |
+| 6 (`extras`, its nearest sibling) | +0.1936 |
+| everything else | ≤ +0.037 |
+
+✅ Right answer on top, 1.4× over second and 7.6× over third. Modest absolute r,
+and a clear ranking — so the method discriminates on this corpus.
+
+### The result
+
+Their capture against all 22 candidate builds:
+
+| build | r |
+|---|---|
+| **`GP_TUTORIAL` build 0** | **+0.4962** |
+| `GP_TUTORIAL` build 1 | +0.3137 |
+| best `GP_SAVE_LOAD` (17) | +0.0713 |
+| worst | −0.0331 |
+
+🟢 **The submenu is a `GP_TUTORIAL` build.** The winning r is *higher* than the
+control's, its margin over second is *better* (1.58× against 1.4×), and both
+TUTORIAL builds sit **4–7× above every `GP_SAVE_LOAD` build** — the archive
+separation is far stronger than the within-archive one.
+
+✅ It is independently plausible: `authored/flow.json` has `ptbtn03` = **TUTORIAL**
+→ `TUTORIAL_MENU`, noted as *"the lesson list is not a `GP_TITLE` build"*. An Ⓐ
+on a menu whose focus was TUTORIAL lands exactly there, and HANDOFF Q5 measured
+initial focus as unstable boot to boot.
+
+⚠️ **What this does and does not settle.** The **archive** is identified with a
+large margin. **Which build within it** is not: 1.58× is the same order as my
+control's 1.4×, and the two TUTORIAL builds are variants of one screen — so I
+would call build 0 the better fit and not a determination.
+
+⚠️ And the method inherits a limit worth stating: an edge map is insensitive to
+*what* the background is, which is the point, but it is also insensitive to a
+missing element that has no edges. It answers "which screen", not "is our render
+complete".