feat: require exact per-mutation capability proof in reviewer reports (Closes #405)

Adds mutation-capability table validation so review_pr cannot authorize
merge or delete mutations without their own exact capability rows.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

final_report_validator.py

@@ -938,6 +938,22 @@ def _rule_reviewer_review_mutation(
     )
 
 
+def _rule_reviewer_mutation_capability_proof(report_text: str) -> list[dict[str, str]]:
+    from reviewer_mutation_capability_proof import assess_mutation_capability_proof
+
+    result = assess_mutation_capability_proof(report_text)
+    if not result.get("block"):
+        return []
+    return _findings_from_reasons(
+        "reviewer.mutation_capability_proof",
+        result.get("reasons") or [],
+        field="Capabilities proven",
+        severity="block",
+        safe_next_action=result.get("safe_next_action")
+        or "document exact per-mutation capability proof before each mutation",
+    )
+
+
 _SHARED_ISSUE_LOCK_RULES = (
     _rule_shared_issue_lock_external_state,
     _rule_shared_manual_lock_pr_override,
@@ -965,6 +981,7 @@ _RULES_BY_TASK: dict[str, list[Callable[..., list[dict[str, str]]]]] = {
         _rule_reviewer_target_branch_freshness,
         _rule_reviewer_mutation_ledger,
         _rule_reviewer_review_mutation,
+        _rule_reviewer_mutation_capability_proof,
     ],
     "reconcile_already_landed": [
         _rule_reconcile_controller_handoff,