fix(db): avoid detached datasource in SQL Server pool creator

backend/apps/db/db.py

@@ -162,7 +162,9 @@ def get_engine(ds: CoreDatasource, timeout: int = 0, use_pool: bool = False) ->
         else:
             engine = create_engine(get_uri(ds), connect_args={"connect_timeout": conf.timeout}, **db_config)
     elif equals_ignore_case(ds.type, 'sqlServer'):
-        engine = create_engine('mssql+pymssql://', creator=lambda: get_origin_connect(ds.type, conf),
+        # A pooled connection may be recreated after the datasource's ORM session closes.
+        ds_type = ds.type
+        engine = create_engine('mssql+pymssql://', creator=lambda: get_origin_connect(ds_type, conf),
                                **db_config)
     elif equals_ignore_case(ds.type, 'oracle'):
         engine = create_engine(get_uri(ds), connect_args={"tcp_connect_timeout": conf.timeout}, **db_config)

backend/tests/test_sqlserver_pool_lifecycle.py

@@ -0,0 +1,84 @@
+"""Regression coverage for issue 1330's SQL Server pool reconnect path."""
+
+import ast
+import json
+import sqlite3
+import threading
+from collections import OrderedDict
+from pathlib import Path
+
+import pytest
+from sqlalchemy import create_engine, text
+from sqlalchemy.orm import make_transient_to_detached, sessionmaker
+from sqlalchemy.pool import NullPool, QueuePool
+from sqlmodel import Session
+
+from apps.datasource.models.datasource import CoreDatasource, DatasourceConf
+
+
+SOURCE = Path(__file__).parents[1] / "apps" / "db" / "db.py"
+
+
+def _load_pool_code(connect):
+    """Load the production functions without importing unrelated DB drivers."""
+    nodes = ast.parse(SOURCE.read_text()).body
+    selected = [node for node in nodes if
+                (isinstance(node, ast.FunctionDef) and node.name == "get_engine") or
+                (isinstance(node, ast.ClassDef) and node.name == "ConnectionPoolManager")]
+
+    def build_engine(url, creator, **options):
+        assert url == "mssql+pymssql://"
+        assert options["pool_recycle"] == 3600
+        # Force a new DBAPI connection at the next checkout rather than waiting an hour.
+        return create_engine("sqlite://", creator=creator, poolclass=QueuePool,
+                             pool_recycle=0)
+
+    namespace = {
+        "CoreDatasource": CoreDatasource,
+        "AssistantOutDsSchema": type("AssistantOutDsSchema", (), {}),
+        "DatasourceConf": DatasourceConf,
+        "Engine": object,
+        "json": json,
+        "aes_decrypt": lambda value: value,
+        "equals_ignore_case": lambda left, right: left.lower() == right.lower(),
+        "create_engine": build_engine,
+        "get_origin_connect": connect,
+        "NullPool": NullPool,
+        "threading": threading,
+        "OrderedDict": OrderedDict,
+        "sessionmaker": sessionmaker,
+    }
+    exec(compile(ast.Module(body=selected, type_ignores=[]), str(SOURCE), "exec"), namespace)
+    return namespace["ConnectionPoolManager"]()
+
+
+@pytest.mark.parametrize("finish", ["commit", "rollback"])
+def test_preview_created_pool_reconnects_after_request_session_closes(finish):
+    connections = []
+
+    def connect(ds_type, conf):
+        connections.append((ds_type, conf.host, conf.database))
+        return sqlite3.connect(":memory:")
+
+    manager = _load_pool_code(connect)
+    metadata_engine = create_engine("sqlite://")
+    configuration = json.dumps({"host": "test-host", "database": "test-db"})
+    datasource = CoreDatasource(id=1330, type="sqlServer", configuration=configuration)
+    make_transient_to_detached(datasource)
+    try:
+        with Session(metadata_engine) as request_session:
+            request_session.add(datasource)
+            with manager.get_pool(datasource)() as sql_session:
+                assert sql_session.execute(text("SELECT 1")).scalar_one() == 1
+            getattr(request_session, finish)()
+
+        # A later chat/MCP request reuses the pool created by the preview request.
+        later_datasource = CoreDatasource(id=1330, type="sqlServer", configuration=configuration)
+        with manager.get_pool(later_datasource)() as sql_session:
+            assert sql_session.execute(text("SELECT 1")).scalar_one() == 1
+        assert len(connections) >= 2
+        assert all(connection == ("sqlServer", "test-host", "test-db")
+                   for connection in connections)
+    finally:
+        manager.close_all()
+        metadata_engine.dispose()