Frozen read-only review gate

Always freeze and verify repository, base/head/parent, canonical patch hash, path set/count, applicability, conflicts, artifacts, and provenance before and after review. Any source or artifact identity drift invalidates the review and requires DO-NOT-MERGE, even when source inspection found no defect. Strict read-only means no edits, tests, builds, services, VCS mutations, or recall when excluded. Treat abbreviated expected blob IDs as prefixes, not mismatches. Report findings first with exact file:line evidence and required severity labels, identify residual risks, and end exactly MERGE or DO-NOT-MERGE.