feat: require MCP-native post-merge cleanup proof (Closes #517)

Add mcp_native_cleanup_proof verifier that blocks raw git branch deletion and
raw API comment deletion scripts as cleanup proof, requires authorized
reconciler MCP tools in cleanup mutation ledgers, and separates merge from
cleanup mutations in controller handoffs.

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

final_report_validator.py

@@ -12,6 +12,7 @@ import re
 from typing import Any, Callable
 
 import issue_lock_provenance
+from mcp_native_cleanup_proof import assess_mcp_native_cleanup_proof
 from post_merge_cleanup_proof import assess_post_merge_cleanup_proof
 from review_proofs import (
     HANDOFF_HEADING,
@@ -1158,12 +1159,30 @@ def _rule_reviewer_post_merge_cleanup_proof(report_text: str) -> list[dict[str,
     )
 
 
+def _rule_shared_mcp_native_cleanup_proof(report_text: str) -> list[dict[str, str]]:
+    result = assess_mcp_native_cleanup_proof(report_text)
+    if not result.get("block"):
+        return []
+    return _findings_from_reasons(
+        "shared.mcp_native_cleanup_proof",
+        result.get("reasons") or [],
+        field="Cleanup mutations",
+        severity="block",
+        safe_next_action=result.get("safe_next_action")
+        or "use authorized reconciler MCP cleanup tools; never raw scripts",
+    )
+
+
 _SHARED_ISSUE_LOCK_RULES = (
     _rule_shared_issue_lock_external_state,
     _rule_shared_manual_lock_pr_override,
     _rule_shared_author_reviewer_same_run,
 )
 
+_SHARED_CLEANUP_PROOF_RULES = (
+    _rule_shared_mcp_native_cleanup_proof,
+)
+
 _RULES_BY_TASK: dict[str, list[Callable[..., list[dict[str, str]]]]] = {
     "review_pr": [
         _rule_shared_controller_handoff,
@@ -1189,12 +1208,14 @@ _RULES_BY_TASK: dict[str, list[Callable[..., list[dict[str, str]]]]] = {
         _rule_reviewer_mutation_ledger,
         _rule_reviewer_review_mutation,
         _rule_reviewer_post_merge_cleanup_proof,
+        *_SHARED_CLEANUP_PROOF_RULES,
         _rule_reviewer_stale_head_proof,
     ],
     "reconcile_already_landed": [
         _rule_reconcile_controller_handoff,
         _rule_shared_email_disclosure,
         *_SHARED_ISSUE_LOCK_RULES,
+        *_SHARED_CLEANUP_PROOF_RULES,
         _rule_reconcile_stale_author_fields,
         _rule_reconcile_eligible_reviewed,
         _rule_reconcile_linked_issue_live,