fix(memory): use asyncio.to_thread for blocking file I/O in aupdate_memory (#2220)

* fix(memory): use asyncio.to_thread for blocking file I/O in aupdate_memory

`_finalize_update` performs synchronous blocking operations (os.mkdir,
file open/write/rename/stat) that were called directly from the async
`aupdate_memory` method, causing `BlockingError` from blockbuster when
running under an ASGI server. Wrap the call with `asyncio.to_thread` to
offload all blocking I/O to a thread pool.

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

* fix(memory): use unique temp filename to prevent concurrent write collision

`file_path.with_suffix(".tmp")` produces a fixed path — concurrent saves
for the same agent (now possible after wrapping _finalize_update in
asyncio.to_thread) would clobber the same temp file. Use a UUID-suffixed
temp file so each write is isolated.

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

* fix(memory): also offload _prepare_update_prompt to thread pool

FileMemoryStorage.load() inside _prepare_update_prompt performs
synchronous stat() and file read, blocking the event loop just like
_finalize_update did. Wrap _prepare_update_prompt in asyncio.to_thread
for the same reason.

The async path now has no blocking file I/O on the event loop:
  to_thread(_prepare_update_prompt) → await model.ainvoke() → to_thread(_finalize_update)

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

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/packages/harness/deerflow/agents/memory/storage.py

@@ -4,6 +4,7 @@ import abc
 import json
 import logging
 import threading
+import uuid
 from datetime import UTC, datetime
 from pathlib import Path
 from typing import Any
@@ -144,7 +145,7 @@ class FileMemoryStorage(MemoryStorage):
             file_path.parent.mkdir(parents=True, exist_ok=True)
             memory_data["lastUpdated"] = utc_now_iso_z()
 
-            temp_path = file_path.with_suffix(".tmp")
+            temp_path = file_path.with_suffix(f".{uuid.uuid4().hex}.tmp")
             with open(temp_path, "w", encoding="utf-8") as f:
                 json.dump(memory_data, f, indent=2, ensure_ascii=False)