fix: 修复 SQLite 连接复用导致数据库不可用

tests/unit/test_db_stability.py

@@ -1,4 +1,5 @@
 import pytest
+from sqlalchemy.pool import NullPool
 
 from app.db import check_database_integrity, checkpoint_sqlite_wal, create_sqlite_engine, ensure_sqlite_schema_compat
 
@@ -11,6 +12,14 @@ def test_check_database_integrity_returns_ok_for_valid_sqlite_database():
         engine.dispose()
 
 
+def test_file_sqlite_engine_does_not_reuse_connections_after_operational_errors(tmp_path):
+    engine = create_sqlite_engine(f"sqlite:///{tmp_path / 'app.db'}")
+    try:
+        assert isinstance(engine.pool, NullPool)
+    finally:
+        engine.dispose()
+
+
 def test_check_database_integrity_raises_when_sqlite_reports_problem(monkeypatch):
     class FakeCursor:
         def execute(self, _sql):