finding(gate): scripts/check-doc-fence-languages.mjs's header still says its scan surface is check-doc-snippet-types' "exactly" and that the coupling pin fails on any differing document list — both stopped being true when PR #8158 added the docs/*.md leg to the snippet gate only #8162

Filed by the domain:devx @ objectui execution seat (PM session session_01FhBNJcLRZLe8M87VcUgpKr, R46, 2026-09-06T21:38Z), from the report on objectui#7856 card 1 (PR #8158, head f011733bf). The dev flagged it as owed follow-up outside that card's file surface (the surface named the gate's TEST, not the gate), and recommended a one-paragraph follow-up card rather than widening a landed PR's surface after the fact. The seat agrees.

What is stale

scripts/check-doc-fence-languages.mjs's header (on f011733bf, unchanged from 571b4870d) states:

1. "The scan surface is check-doc-snippet-types's, exactly: …" — no longer exact. PR feat(gate): bring the root docs/*.md pages into the doc-snippet walk #8158 gave the snippet gate a docs/*.md leg (ROOT_DOCS / rootDocsPages()); check:doc-fences did not gain it, by design (its surface is not objectui#7856 card 1's to move).
2. The coupling pin "fails if they ever return different document lists" — it no longer asserts plain equality. scripts/__tests__/check-doc-fence-languages.test.ts's walks exactly the documents the snippet gate walks now subtracts exactly rootDocsPages() from the snippet gate's walk before comparing, and pins that the subtraction is non-empty and that the leg stops above docs/adr/ and docs/audits/ in both walks.

Why prose, not enforcement

Nothing is unguarded: the pin itself carries the accurate statement and fails on any other drift. The header is what a reader (or an agent) reads first, and it now promises a stronger equality than the pin holds. The fix is a one-paragraph header edit on that gate naming the divergence and its reason (objectui#7856 card 1 / card 2 boundary), and no test change.

Verification recipe

git fetch origin main
git show origin/main:scripts/check-doc-fence-languages.mjs | grep -n -A3 "scan surface"
git show origin/main:scripts/__tests__/check-doc-fence-languages.test.ts | grep -n "rootDocsPages"

Routing note: this could ride with objectui#7856 card 2 (the governed docs/adr/** half, another seat's PR) but should not — it is an ungoverned one-header edit and card 2 stops in draft for a human, which would delay this correction for no benefit.

Refs objectui#7856, PR #8158.