feat: enforce reconciler PR-close proof fields in final reports (Closes #306)

Closes #306.

The dedicated reconciler close path (profile, gated close tool, ancestor
proof, tests) already shipped across #301/#304/#309/#310, but the
final-report validator did not require a reconciler close to prove itself.
A handoff could report `PRs closed: #N` while omitting the close
capability, ancestor proof, or linked-issue result and still grade A.

This adds the missing report-time enforcement.

Changes:
- final_report_validator.py — new `reconcile.close_proof_fields` rule
  (`_rule_reconcile_close_proof`). Fires only when a PR close is reported
  (via the `PRs closed` field or a `reconciler_close_lock`), then blocks
  unless the handoff carries close capability proof (gitea.pr.close),
  ancestor proof, PR close result, and linked-issue result. Comment-only
  and blocked reconciliations are unaffected. New optional
  `reconciler_close_lock` kwarg on `assess_final_report_validator`.
- tests/test_final_report_validator.py — TestReconcilerCloseProof (6 cases):
  full-proof close passes; missing capability / ancestor / linked-issue
  result each block; session close lock requires proof; comment-only
  needs no close proof.
- reconcile-landed-pr.md — §18A documents the enforced gate.

Validation:

  venv/bin/python -m pytest tests/test_final_report_validator.py \
    tests/test_reconciler_close_gate.py tests/test_already_landed_reconcile.py \
    tests/test_reconcile_already_landed_pr_tool.py \
    tests/test_reconciliation_workflow.py tests/test_review_proofs.py -q

289 passed.

Worktree: branches/issue-306-reconciler-close-proof

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

final_report_validator.py

@@ -816,6 +816,69 @@ def _rule_reconcile_linked_issue_live(
     return []
 
 
+_PR_CLOSE_NEGATIVE = frozenset({"", "none", "n/a", "na", "0", "no", "not closed", "not performed"})
+_ANCESTOR_AFFIRMATIVE_RE = re.compile(
+    r"ancestor|passed|true|verified|confirmed", re.IGNORECASE
+)
+
+
+def _reconciler_pr_close_performed(fields: dict[str, str], lock: dict) -> bool:
+    """True when the report/session indicates a reconciler PR close happened."""
+    if lock.get("pr_closed") is True:
+        return True
+    value = (fields.get("prs closed", "") or "").strip().lower()
+    if value in _PR_CLOSE_NEGATIVE:
+        return False
+    # A closed PR is reported by number (e.g. "#99") or an affirmative result.
+    return bool(re.search(r"#\s*\d+|\b(?:closed|success|done)\b", value))
+
+
+def _rule_reconcile_close_proof(
+    report_text: str,
+    *,
+    reconciler_close_lock: dict | None = None,
+) -> list[dict[str, str]]:
+    """#306: a reconciler PR close must carry exact proof fields.
+
+    Read-only/comment-only reconciliations are untouched. Once a PR close is
+    reported (via the ``PRs closed`` field or a session close lock), the
+    handoff must prove the close capability, ancestor landing, PR close
+    result, and the linked-issue result — narrative alone fails closed.
+    """
+    fields = _handoff_fields(report_text)
+    lock = reconciler_close_lock or {}
+    if not _reconciler_pr_close_performed(fields, lock):
+        return []
+
+    missing: list[str] = []
+    capabilities = fields.get("capabilities proven", "")
+    if "gitea.pr.close" not in capabilities.lower():
+        missing.append("close capability proof (gitea.pr.close)")
+    ancestor = fields.get("ancestor proof", "")
+    if not _ANCESTOR_AFFIRMATIVE_RE.search(ancestor):
+        missing.append("ancestor proof")
+    prs_closed = (fields.get("prs closed", "") or "").strip().lower()
+    if prs_closed in _PR_CLOSE_NEGATIVE and lock.get("pr_closed") is True:
+        missing.append("PR close result")
+    linked = fields.get("linked issue live status", "") or fields.get("issues closed", "")
+    if not linked.strip():
+        missing.append("linked issue result")
+
+    if not missing:
+        return []
+    return [
+        validator_finding(
+            "reconcile.close_proof_fields",
+            "block",
+            "Reconciler close proof",
+            "reconciler PR close reported without required proof field(s): "
+            + ", ".join(missing),
+            "include close capability proof, ancestor proof, PR close result, "
+            "and linked issue result in the handoff",
+        )
+    ]
+
+
 def _rule_reconcile_pagination_proof(report_text: str) -> list[dict[str, str]]:
     text = report_text or ""
     if not _INVENTORY_COMPLETE_RE.search(text):
@@ -916,6 +979,7 @@ _RULES_BY_TASK: dict[str, list[Callable[..., list[dict[str, str]]]]] = {
         _rule_reconcile_stale_author_fields,
         _rule_reconcile_eligible_reviewed,
         _rule_reconcile_linked_issue_live,
+        _rule_reconcile_close_proof,
         _rule_reconcile_pagination_proof,
         _rule_reviewer_git_fetch_readonly,
         _rule_reviewer_legacy_workspace_mutations,
@@ -1006,6 +1070,7 @@ def assess_final_report_validator(
     issue_filing_lock: dict | None = None,
     session_pr_opened: bool = False,
     validation_session: dict | None = None,
+    reconciler_close_lock: dict | None = None,
 ) -> dict[str, Any]:
     """Validate final-report text against task-specific proof rules (#327).
 
@@ -1062,6 +1127,7 @@ def assess_final_report_validator(
         "local_edits": local_edits,
         "session_pr_opened": session_pr_opened,
         "validation_session": validation_session,
+        "reconciler_close_lock": reconciler_close_lock,
     }
 
     for rule in _RULES_BY_TASK.get(normalized_kind, ()):