docs(#535): add guidance for updating stale cross-references

[fullsend-ai-coder]

When implementing a feature previously described as in progress, coming soon, or planned in the docs, authors should search for and update those references in the same PR. This prevents stale status notes from persisting after a feature ships.

The review agent repeatedly flagged a stale "still in progress" note for public mint mode across 7 consecutive review runs on PR fullsend-ai#2773, but no convention existed to cite. This bullet gives both authors and reviewers an actionable rule.

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Closes #535

Post-script verification

• Branch is not main/master (agent/535-stale-cross-ref-guidance)
• Secret scan passed (gitleaks — b776cf6006a12016eaa21412dc65a3001100e801..HEAD)
• Pre-commit hooks passed (authoritative run on runner)
• Tests ran inside sandbox

[fullsend-ai-review]

🤖 Finished Review · ✅ Success · Started 5:41 PM UTC · Completed 5:46 PM UTC
Commit: b776cf6 · View workflow run →

[fullsend-ai-review]

Review — Approve

1-line docs change to AGENTS.md adding contributor guidance for updating stale cross-references when implementing previously-described features.

Evaluated dimensions

Dimension	Result
Correctness	✅ Guidance is technically sound — suggested grep terms are reasonable heuristics for finding stale forward-references. Internally consistent with existing AGENTS.md bullets.
Security	✅ No secrets, injection patterns, prompt injection, Unicode steganography, or permission changes.
Intent & coherence	✅ Directly authorized by #535. Scope matches: single bullet adding a process convention to the documented home for contributor guidance. No scope creep.
Style & conventions	✅ Follows existing formatting — imperative tone, inline code for grep terms, consistent length and complexity with surrounding bullets.
Docs currency	✅ No duplication or contradiction with existing guidance elsewhere in the repo.
Cross-repo contracts	⏭ Skipped — no exported APIs or schemas modified.

Summary

Clean change. The new bullet addresses a real, documented problem (issue #535 — review agent flagged stale "in progress" references across 7 consecutive runs on PR fullsend-ai#2773 without resolution). The guidance is actionable, minimal, and well-placed in the "How to work in this repo" section.

No findings at or above the low severity threshold.

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Protected paths detected — this PR modifies files under one or more
protected paths. The review agent cannot approve PRs that touch these paths.
A human reviewer must approve this PR.

Protected files in this PR:

• AGENTS.md

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Labels: PR adds contributor documentation guidance to AGENTS.md