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/updater.py

@@ -394,7 +394,8 @@ class MemoryUpdater:
     ) -> bool:
         """Update memory asynchronously based on conversation messages."""
         try:
-            prepared = self._prepare_update_prompt(
+            prepared = await asyncio.to_thread(
+                self._prepare_update_prompt,
                 messages=messages,
                 agent_name=agent_name,
                 correction_detected=correction_detected,
@@ -406,7 +407,8 @@ class MemoryUpdater:
             current_memory, prompt = prepared
             model = self._get_model()
             response = await model.ainvoke(prompt)
-            return self._finalize_update(
+            return await asyncio.to_thread(
+                self._finalize_update,
                 current_memory=current_memory,
                 response_content=response.content,
                 thread_id=thread_id,