feat: require live PR head re-pin before conflict-fix classification (Closes #522)

Treat inventory mergeable/head as advisory. Add classification helper and
MCP tool so author sessions re-pin the live PR head before creating a
conflict-fix worktree, skip stale inventory false-negatives, and prove
classification in final reports.

final_report_validator.py

@@ -565,6 +565,27 @@ def _rule_reviewer_stale_head_proof(report_text: str) -> list[dict[str, str]]:
     )
 
 
+def _rule_conflict_fix_classification_proof(report_text: str) -> list[dict[str, str]]:
+    from conflict_fix_classification import (
+        assess_conflict_fix_classification_final_report,
+    )
+
+    text = report_text or ""
+    result = assess_conflict_fix_classification_final_report(text)
+    if result.get("proven"):
+        return []
+    return _findings_from_reasons(
+        "author.conflict_fix_classification_proof",
+        result.get("reasons") or [],
+        field="Conflict-fix classification",
+        severity="block",
+        safe_next_action=(
+            "call gitea_assess_conflict_fix_classification, state the live head "
+            "SHA, and state the classification before creating a conflict-fix worktree"
+        ),
+    )
+
+
 def _rule_conflict_fix_push_proof(report_text: str) -> list[dict[str, str]]:
     from pr_work_lease import assess_conflict_fix_final_report
 
@@ -1271,6 +1292,7 @@ _RULES_BY_TASK: dict[str, list[Callable[..., list[dict[str, str]]]]] = {
         *_SHARED_ISSUE_LOCK_RULES,
         _rule_shared_issue_acceptance_gate,
         _rule_reviewer_vague_mutations_none,
+        _rule_conflict_fix_classification_proof,
         _rule_conflict_fix_push_proof,
         _rule_worktree_cleanup_audit_proof,
     ],