feat: require canonical next-action state comments (#495)

Add canonical issue/PR/discussion state comment templates and validators,
final-report rules for STATE/WHO_IS_NEXT/NEXT_ACTION/NEXT_PROMPT, and
queue-controller guidance. Posting enforcement remains in #496.

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

tests/test_final_report_validator.py

@@ -345,6 +345,92 @@ class TestReconciliationRules(unittest.TestCase):
         )
 
 
+class TestCanonicalStateUpdateRules(unittest.TestCase):
+    def test_claimed_state_comment_without_block_blocks(self):
+        report = _reconcile_handoff() + "\nPosted canonical state comment on PR #99."
+        result = assess_final_report_validator(report, "reconcile_already_landed")
+        self.assertTrue(result["blocked"])
+        self.assertTrue(
+            any(f["rule_id"] == "shared.canonical_state_update" for f in result["findings"])
+        )
+
+    def test_state_comment_missing_next_prompt_blocks(self):
+        report = (
+            _reconcile_handoff()
+            + """
+
+## Canonical PR State
+
+STATE:
+needs-review
+
+WHO_IS_NEXT:
+reviewer
+
+NEXT_ACTION:
+Review PR #99.
+
+NEXT_PROMPT:
+
+ISSUE:
+#98
+
+HEAD_SHA:
+0fdc8f582026b72a229d59a172c0a63ac4aaeaf9
+
+REVIEW_STATUS:
+none
+
+MERGE_READY:
+no
+"""
+        )
+        result = assess_final_report_validator(report, "reconcile_already_landed")
+        self.assertTrue(result["blocked"])
+        reasons = " ".join(f["reason"] for f in result["findings"])
+        self.assertIn("NEXT_PROMPT", reasons)
+
+    def test_valid_state_comment_claim_passes_shared_rule(self):
+        report = (
+            _reconcile_handoff()
+            + """
+
+## Canonical PR State
+
+STATE:
+needs-review
+
+WHO_IS_NEXT:
+reviewer
+
+NEXT_ACTION:
+Review PR #99 against the pinned head.
+
+NEXT_PROMPT:
+Load the review workflow and review PR #99.
+
+ISSUE:
+#98
+
+HEAD_SHA:
+0fdc8f582026b72a229d59a172c0a63ac4aaeaf9
+
+REVIEW_STATUS:
+none
+
+MERGE_READY:
+no
+
+BLOCKERS:
+none
+"""
+        )
+        result = assess_final_report_validator(report, "reconcile_already_landed")
+        self.assertFalse(
+            any(f["rule_id"] == "shared.canonical_state_update" for f in result["findings"])
+        )
+
+
 class TestCanonicalReconcileSchema(unittest.TestCase):
     """Issue #307: reconciliation workflows emit only the canonical schema."""