One-shot second-opinion diff review by a different-model seat, advisory only

Failure modes

Risk areas

• Absent seat — the seat CLI is missing or unauthenticated. The run records absent with the exit code and reply head; this is a valid outcome, not an error to retry blindly.
• Board unreachable — local Redis down. The review still runs; the result records board: skipped (<reason>).
• Oversized diff — files beyond the 60k budget are omitted and named in the manifest. A review that saw only part of the diff says so everywhere the result renders.
• Format noncompliance — a seat that replies in prose is reported as format_noncompliant with the raw reply preserved. Findings are never fabricated from prose.

Diagnosis order

1. status first: absent → check the seat CLI and its auth; format_noncompliant → read the raw reply.
2. manifest next: were the files you care about in sent?
3. board last: skipped (...) names the reason; the review itself is unaffected.