port: record the P0 gate, verified -- and name the gap it belongs to

They were right that the P0/P2/P5 gap matters more than the P2 fix. P0 is the one
of the three I can close alone: its gate names no human and no emulator.

Verified both halves. export/screens/title/main_menu.json exists at 51011 bytes,
the validator reports 16 screens validating against sylpheed.screen/3 with that
file among them, and all 20 sprites it references open as PNG with 0 missing and 0
unreadable. P0's gate is met on an artifact and now written down; it had been met
for a long time and only the record was missing.

That is the argued-versus-indexed split one level up. The refutation register
taught it about deaths -- the page is where a refutation is argued, the index is
where it is found. Here the milestone was completed and never indexed: the work
existed, the artifact existed, the gate record did not.

Remaining: P2 verified and recorded last iteration; P5 is 'a human clicks through
it', which I cannot self-certify and will not try. Converting it into something I
can check would be rewriting the gate to fit the checker, which is the mission's
own warning about gating on 'it compiles' in a more flattering costume.

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 -->
 
-226 sections. Search this before re-deriving anything.
+227 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)
@@ -237,6 +237,7 @@ dies, which is what this file is for.
 * [Their `REFUTED.md` gap, in my tree — where I already had the mechanism and fed it nothing](#their-refutedmd-gap-in-my-tree--where-i-already-had-the-mechanism-and-fed-it-nothing)
 * [Building the withdrawal-time hook — the thing we agreed neither of us was about to close](#building-the-withdrawal-time-hook--the-thing-we-agreed-neither-of-us-was-about-to-close)
 * [Applying "a correction is a new claim" to my own most recent correction](#applying-a-correction-is-a-new-claim-to-my-own-most-recent-correction)
+* [P0 gate — recorded at last, and the gap it belongs to](#p0-gate--recorded-at-last-and-the-gap-it-belongs-to)
 
 <!-- /INDEX -->
 ## P0 — the exporter, 2026-08-28
@@ -11900,3 +11901,42 @@ clicks through it"*, which I cannot self-certify at all.
 was written, indexed, and would have passed my own withdrawal-time hook cleanly.
 **Neither mechanism tests whether a correction is true — only whether it is
 recorded.** They enforce bookkeeping and cannot enforce accuracy.
+
+## P0 gate — recorded at last, and the gap it belongs to
+
+They were right that the P0/P2/P5 finding matters more than the P2 fix. **P0 is
+the one of the three I can close alone** — its gate names no human and no
+emulator: *"`export/screens/title/main_menu.json` validates against FORMAT.md and
+the PNGs open."*
+
+| | |
+|---|---|
+| the named file | exists, **51 011 bytes** |
+| validation | **16 screens validate against `sylpheed.screen/3`**, that file among them |
+| sprites it references | **20** |
+| open as PNG | **20** — 0 missing, 0 unreadable |
+
+✅ **P0's gate is met, on an artifact, and now written down.** It had been met for
+a very long time; what was missing was the record.
+
+### The shape this belongs to
+
+📌 That is the **argued-versus-indexed split one level up**. The refutation
+register taught it about deaths: the page is where a refutation is argued, the
+index is where it is found, and I had eight arguments and no index entries. **Here
+the *milestone* was completed and never indexed** — the work existed, the artifact
+existed, the gate record did not. Same failure, different object.
+
+⚠️ **Remaining, and stated rather than quietly finished:**
+
+* **P2** — verified last iteration (buttons slide: changed region 307×215 at
+  (542, 162), matching the declared button), recorded there.
+* **P5** — *"a human clicks through it."* ❌ **I cannot self-certify this and will
+  not try.** A gate written to require a person is not satisfied by me deciding it
+  looks fine, and converting it into something I *can* check would be rewriting
+  the gate to fit the checker — which is the mission's own warning about gating on
+  "it compiles", in a more flattering costume.
+
+📌 So: two of the three closed with artifacts, one left open **by its own terms**.
+Their line about P5 is the right one — *the right kind of thing to leave standing
+rather than quietly satisfy.*