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]>

final_report_validator.py

@@ -1042,10 +1042,29 @@ def _rule_reviewer_review_mutation(
     )
 
 
+def _rule_shared_canonical_state_update(report_text: str) -> list[dict[str, str]]:
+    from canonical_state_comments import validate_final_report_state_update
+
+    result = validate_final_report_state_update(report_text)
+    if not result.get("applicable") or result.get("valid"):
+        return []
+    return [
+        validator_finding(
+            "shared.canonical_state_update",
+            "block",
+            "Canonical state update",
+            reason,
+            "include a canonical state block with STATE, WHO_IS_NEXT, NEXT_ACTION, and NEXT_PROMPT",
+        )
+        for reason in (result.get("reasons") or ["invalid canonical state update"])
+    ]
+
+
 _SHARED_ISSUE_LOCK_RULES = (
     _rule_shared_issue_lock_external_state,
     _rule_shared_manual_lock_pr_override,
     _rule_shared_author_reviewer_same_run,
+    _rule_shared_canonical_state_update,
 )
 
 _RULES_BY_TASK: dict[str, list[Callable[..., list[dict[str, str]]]]] = {