Move async SQLite mkdir off the event loop (#1921)

Co-authored-by: DanielWalnut <45447813+hetaoBackend@users.noreply.github.com>

backend/packages/harness/deerflow/agents/checkpointer/async_provider.py

@@ -17,6 +17,7 @@ For sync usage see :mod:`deerflow.agents.checkpointer.provider`.
 
 from __future__ import annotations
 
+import asyncio
 import contextlib
 import logging
 from collections.abc import AsyncIterator
@@ -54,7 +55,7 @@ async def _async_checkpointer(config) -> AsyncIterator[Checkpointer]:
             raise ImportError(SQLITE_INSTALL) from exc
 
         conn_str = resolve_sqlite_conn_str(config.connection_string or "store.db")
-        ensure_sqlite_parent_dir(conn_str)
+        await asyncio.to_thread(ensure_sqlite_parent_dir, conn_str)
         async with AsyncSqliteSaver.from_conn_string(conn_str) as saver:
             await saver.setup()
             yield saver