refactor(db): 修复异步连接池无界增长，并完成 SQLAlchemy 2.0 迁移与分层归位 (#6320)

tests/test_db_error_diagnostics.py

@@ -4,7 +4,11 @@ import pytest
 from sqlalchemy import create_engine, text
 from sqlalchemy.exc import OperationalError
 
-import app.db as db_module
+# 诊断实现已迁至 app.db.diagnostics；app.db 只做 re-export，私有符号不在其上
+import app.db.diagnostics as db_module
+# 用 getter 而不是旧名字 AsyncEngine：后者只为仓库外插件保留，模块级导入它会在 pytest
+# 的收集期就把全局异步引擎建出来
+from app.db.engine import get_global_async_engine
 
 
 class _SqliteError(Exception):
@@ -62,7 +66,7 @@ def test_database_error_listener_omits_statement_and_parameters(monkeypatch) ->
     """数据库错误日志不得包含 SQL、参数或驱动返回的原始消息。"""
     messages = []
     engine = create_engine("sqlite:///:memory:")
-    monkeypatch.setattr("app.db.logger.error", messages.append)
+    monkeypatch.setattr("app.db.diagnostics.logger.error", messages.append)
     db_module._register_database_error_logging(engine)
 
     with pytest.raises(OperationalError):
@@ -84,10 +88,10 @@ def test_database_error_listener_omits_statement_and_parameters(monkeypatch) ->
 def test_async_database_engine_logs_driver_error_metadata(monkeypatch) -> None:
     """异步 Engine 应通过底层 sync engine 记录驱动错误码。"""
     messages = []
-    monkeypatch.setattr("app.db.logger.error", messages.append)
+    monkeypatch.setattr("app.db.diagnostics.logger.error", messages.append)
 
     async def query_missing_table() -> None:
-        async with db_module.AsyncEngine.connect() as connection:
+        async with get_global_async_engine().connect() as connection:
             await connection.execute(text("SELECT * FROM async_missing_table"))
 
     with pytest.raises(OperationalError):