diff --git a/routes/admin_observability_routes.py b/routes/admin_observability_routes.py
index 730b7a6..8c52ccd 100644
--- a/routes/admin_observability_routes.py
+++ b/routes/admin_observability_routes.py
@@ -1834,13 +1834,13 @@ def ai_calls_trigger_code_review():
             ['git', 'rev-parse', 'HEAD'], stderr=subprocess.DEVNULL,
         ).decode().strip()
         changed = subprocess.check_output(
-            ['git', 'diff-tree', '--no-commit-id', '--name-only', '-r', commit_sha],
+            ['git', 'diff-tree', '--no-commit-id', '--name-only', '-r', '-m', commit_sha],
             stderr=subprocess.DEVNULL,
         ).decode().strip().split('\n')
-        changed = [f for f in changed if f]
+        changed = list(dict.fromkeys(f for f in changed if f))
 
         if not changed:
-            return jsonify({'ok': False, 'error': '最新 commit 無變更檔案'}), 400
+            return jsonify({'ok': False, 'error': '最新 commit 無變更檔案'}), 503
 
         pipeline = CodeReviewPipeline(
             commit_sha=commit_sha,