docs(devlog): record the release-notes fallback and the v2.20.0 release

[lidge-jun]

Summary

Devlog record for the release-notes fallback (#1766) and the v2.20.0 release: the measured PR-association collapse that produced 169-char stub bodies, the seven blockers folded across three review rounds, and the promotion/release evidence.

Verification

Docs-only; evidence cited inline.

Checklist

• Targets dev
• No code changes

Summary by CodeRabbit

• Documentation
  • Documented the release-notes issue affecting versions 2.18.2 and 2.19.0.
  • Added details about the commit-log fallback and regression coverage.
  • Recorded the updated release process for version 2.20.0, including verification results and review findings.
  • Confirmed that the fallback was not required for the 2.20.0 release.

[github-actions]

✅ Deterministic PR hygiene checks passed.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 30e48c2e-c25c-46fb-a0d1-58213dcf3f7d

📥 Commits

Reviewing files that changed from the base of the PR and between c71c827 and 86f625b.

📒 Files selected for processing (1)

• devlog/_plan/260815_old_draft_triage/040_release_notes_fallback.md

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📝 Walkthrough

Walkthrough

The release notes document records the v2.18.2 and v2.19.0 defect, the commit-log fallback behavior and regression coverage, and v2.20.0 release verification.

Changes

Release notes fallback

Layer / File(s)	Summary
Defect and fallback behavior devlog/_plan/260815_old_draft_triage/040_release_notes_fallback.md	Documents the stub release-note defect, fallback categorization, security and correctness fixes, and regression tests.
Release verification devlog/_plan/260815_old_draft_triage/040_release_notes_fallback.md	Records v2.20.0 release wiring, exact-SHA CI results, verification, and the fact that the fallback did not execute.

Estimated code review effort: 1 (Trivial) | ~3 minutes

Possibly related PRs

• lidge-jun/opencodex#1766: Implements the release-notes fallback documented by this change.

Suggested reviewers: ingwannu

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch docs/260815-release-2200

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[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 86f625bb8c

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[chatgpt-codex-connector]

Move the completed unit out of _plan

This verification records the successful v2.20.0 release and leaves no remaining work, but the unit remains under devlog/_plan/, so repository triage will continue to classify completed work as open. Move the entire 260815_old_draft_triage unit to devlog/_fin/, or explicitly document the work that is still outstanding if the unit is intentionally open.

AGENTS.md reference: AGENTS.md:L75-L78

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