Capture provenance contract

The top-level capture exec command remains a diagnostic command. It may run in a dirty checkout, a non-Git directory, or a checkout that produces temporary review artifacts. The capture buffer records the execution root, the active ReviewPlan and Assignment when one is available, the start and end hashes of the plan's frozen subjects, and the start/end Git commit when Git can report one. A capture without a current plan is marked diagnostic-only.

runtime review-result submit validates a command_output: reference against its persisted file, digest, byte count, and truncation metadata. A withheld or truncated stream, an environment-presence marker, and an artifact change marker are observation metadata; they cannot certify a passing Claim. A PASS that cites an automatic command-output artifact must also provide the capture buffer and matching provenance. The captured frozen subjects must match the registered ReviewPlan at both ends of the command window, and a commit change during the command rejects that PASS. Dirty control-plane, documentation, report, and temporary review-artifact surfaces remain allowed; undeclared product files in the execution checkout are recorded as product drift and reject that PASS.

Older hand-authored capture step JSON remains readable. Hash-bound manual path: evidence under ordinary repository surfaces continues to support diagnostic and review flows. A path rewritten to point into the automatic capture exec surface is treated as automatic evidence and cannot bypass the capture provenance check by omitting --captures.