chore(ratchet): raise the AGENTS.md ceiling 961 -> 969 per the maintainer ruling

The one-line follow-up PR #11908's body pre-wrote: the published-spellings
mirror re-sync costs +8 lines, lossless rewrap headroom measured 0, and the
mirror is now mechanically enforced. Maintainer ruling 2026-08-25, verbatim:
「同意，帮我合并，然后继续」 (option A as presented in the PM-chat batch
review; provenance on PR #11908).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01H9StxQgG2DPA26XzZZqnJB

Author: claude

scripts/pm/check-skill-line-ratchet.mjs

@@ -186,7 +186,18 @@ export const CEILINGS = new Map([
   // 2026-08-20, verbatim and untranslated: 「A — 抬上限到 961 (Recommended)」
   // (issue #10126, comment 5353111732). Headroom is 0 again by construction, and
   // the next author needing a line is back to compressing.
-  ['AGENTS.md', 961],
+  //
+  // 961 → 969 (#10855 / PR #11908): the published-spellings mirror re-sync. The
+  // AGENTS.md copy of check-cross-package-test-inputs' recognised-spellings list
+  // had drifted (the findUp anchor seeds missing), the honest re-sync costs +8
+  // lines, and lossless rewrap headroom across the section measured 0 — so it
+  // could not be paid in place. The mirror is now mechanically enforced by
+  // check-published-list-mirrors.mjs, which prices any later drift at the moment
+  // it is incurred. Maintainer ruling 2026-08-25, verbatim and untranslated:
+  // 「同意，帮我合并，然后继续」 — accepting option A (raise to 969) as presented
+  // in the PM-chat batch review; provenance recorded on PR #11908. Headroom is 0
+  // again by construction.
+  ['AGENTS.md', 969],
   // #9965: root CLAUDE.md is the other repo-root instruction file — same read
   // path (every seat session), same governance (Prime Directive #14). It is
   // structurally growth-prone in the way the ratchet is built for: it exists to