fix(validator): align final-report validator with canonical schema (Closes #698)

Fixes the final-report validator defects from Issue #698 (original lead
plus the independent reproduction recorded during the PR #703 formal
review, comment 11246):

- Legacy fields: the review/merger required-field tables no longer demand
  'Pinned reviewed head', 'Scratch worktree used', 'Worktree path',
  'Worktree dirty', 'Mutations', 'Next', 'Issue/PR', 'Branch/SHA', or
  'Files changed' — names the canonical review-merge-final-report schema
  forbids or replaces. The canonical names ('Reviewed head SHA', 'Review
  worktree path/dirty', 'Safe next action', mutation categories) are
  required instead, with backward-compatible aliases where the schema
  permits them.
- Structured proof: workflow-load helper results are recognized in
  colon, key=value, and JSON renderings; validation pass proof is
  accepted anywhere in the Validation field value (for example
  'focused 50 passed; full 2665 passed').
- Mutation inference: review mutations are inferred only from
  authoritative evidence (performed=true and not gated); read-only
  diagnostics and pre-API rejections no longer count as mutations.
- Lease release vs cleanup: canonical reviewer lease release (release
  tool call or terminal phase=released marker) is lease lifecycle, not
  post-merge cleanup, and no longer triggers the branch/worktree cleanup
  checklist; genuine delete/remove claims still require full proof.
- Blocked reports: a legitimately blocked run that states an explicit
  'Reviewed/Candidate head SHA: none' with no verdict, merge, or started
  validation owes no head proofs; approval-time and merge-time live-head
  proofs are demanded only once the corresponding phase begins, and a
  report that states no head at all still fails closed.
- action_log robustness: malformed (non-dict) entries and non-list logs
  are reported as clear sanitized findings (position and type only, no
  content echo) instead of crashing with AttributeError; a defective
  validator rule now fails closed with a sanitized block finding rather
  than raising a secondary exception.

27 new regression tests, including canonical fixtures modeled on the
PR #703 formal-review handoff and the blocked preflight report from the
prior #698 reproductions. Two legacy-field test fixtures updated to the
canonical schema. Full suite: 2663 passed, 6 skipped, 161 subtests.

Co-Authored-By: Claude Fable 5 <[email protected]>

review_final_report_schema.py

@@ -25,8 +25,13 @@ _REVIEWED_HEAD_RE = re.compile(
     r"(?:pinned reviewed head|reviewed head sha)\s*:\s*([0-9a-f]{7,40})",
     re.IGNORECASE,
 )
+# #698: validation pass proof appears in several legitimate shapes —
+# "Validation: pass", "Validation: focused 50 passed; full 2665 passed",
+# or structured "validation_status: pass". Accept pass evidence anywhere in
+# the Validation field's value, not only as its first token.
 _VALIDATION_PASS_RE = re.compile(
-    r"validation\s*:\s*(?:pass|passed|strong|ok|green)",
+    r"validation(?:_status)?\s*:[^\n]{0,300}?"
+    r"(?:\bpass(?:ed)?\b|\bstrong\b|\bok\b|\bgreen\b|\d+\s+passed)",
     re.IGNORECASE,
 )
 _MERGED_CLAIM_RE = re.compile(