fix(test): 更新 TestHistoryMessageFormat 適配 Phase 27 雙層策略

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/api/tests/test_telegram_adr050.py

@@ -120,8 +120,10 @@ class TestHistoryMessageFormat:
         assert "count_30d" in source
 
     def test_history_handles_no_stats(self):
-        """history 處理無頻率統計資料的情況"""
-        assert "無頻率統計資料" in self._read_gateway()
+        """history 處理無頻率統計資料的情況 (Phase 27: 舊 incident 無 DB 快照)"""
+        source = self._read_gateway()
+        # Phase 27 雙層策略: 無快照時顯示說明，而非舊版 "無頻率統計資料"
+        assert "無建立時快照" in source or "無頻率統計資料" in source
 
 
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