[Klaud Cold] AGENTS.md: sync codeowner-signoff-verify.yml with PR_REVIEW_CHECKLIST.md updates

[functionstackx]

Summary

• Adds a "Checklist ↔ sign-off verifier sync" rule to AGENTS.md: docs/PR_REVIEW_CHECKLIST.md is the source of truth for the merge standard, and whenever its policy items change (added/removed/materially reworded), agents are allowed and expected to update the checks in codeowner-signoff-verify.yml to match — ideally in the same PR.
• Notes the boundaries: cosmetic/formatting/_zh-sync edits need no verifier change, and Check 5 already catches stale sign-off templates automatically; only new/removed policy items need check-logic changes.
• Documents the validation recipe used in [Klaud Cold] Align codeowner-signoff-verify with latest PR_REVIEW_CHECKLIST.md #2015: merge, throwaway [DO NOT MERGE] test PR, sign-off comment containing the exact trigger phrase, read the verdict, close.

Test plan

• Docs-only (agent guidance); no runtime surface.

🤖 Generated with Claude Code

[claude]

LGTM — docs-only agent-guidance addition to AGENTS.md documenting the checklist ↔ verifier sync rule.

Extended reasoning...

Overview

This PR adds a single paragraph to AGENTS.md documenting a "Checklist ↔ sign-off verifier sync" rule — declaring docs/PR_REVIEW_CHECKLIST.md as the source of truth for the merge standard, and instructing agents to update .github/workflows/codeowner-signoff-verify.yml when checklist policy items are added/removed/materially reworded. It also notes cosmetic-edit exceptions and documents the validation recipe (throwaway [DO NOT MERGE] test PR).

Security risks

None. This is a text-only edit to an agent-instruction file. No runtime code, no workflows, no permissions, no secrets. AGENTS.md is an explicit _zh-exemption per the file's own docs rule, so no bilingual mirror is required.

Level of scrutiny

Very low. The change is a docs-only, self-contained addition of guidance for future agents. There is no logic, no configuration, no CI wiring modified. The paragraph is internally consistent with the surrounding AGENTS.md conventions (bilingual rules, _zh exceptions, Check 5 semantics).

Other factors

The added guidance is accurate about the workflow's behavior (Check 5 dynamically loads the checklist, trigger phrase is required) and references the correct validation approach used in PR #2015. Content is coherent, no contradictions with existing sections.