PR Review Agent: run #715 aborted early — 3 failure modes identified

[don-petry]

Summary

Run #715 of the PR Review Agent (scheduled, 2026-05-12) processed only 2 of 20 candidates before aborting early. Three distinct failure modes cascaded to cause the abort.

Failure sequence

1. Claude opus-4-7 hit a rate limit during the approval-confirmation step for ContentTwin/pull/72.
2. Gemini fallback was unavailable — CLI not installed / no GOOGLE_API_KEY — so the session fell through to the Copilot engine.
3. Copilot CLI triage command was rejected with error: Invalid command format. The rate-limit detector misclassified this as a rate-limit hit (exit 2), leaving no fallback and aborting the session with 18 PRs unprocessed.

Sub-issues

• fix: Gemini fallback unavailable when Claude is rate-limited (no CLI / no GOOGLE_API_KEY) #146 — Gemini fallback unavailable: no buffer when Claude is exhausted
• fix: Copilot CLI triage command rejected with 'Invalid command format' #147 — Copilot CLI triage command format rejected
• fix: rate-limit detector too broad — misclassifies CLI format errors as rate limits #148 — Rate-limit detector too broad: catches non-rate-limit CLI errors

Impact

18 PR candidates skipped in a single run; any run where Claude is rate-limited on the approval path is now fully unprotected.