fix: Memory update system has cache corruption, data loss, and thread-safety bugs (#2251)

* fix(memory): cache corruption, thread-safety, and caller mutation bugs

Bug 1 (updater.py): deep-copy current_memory before passing to
_apply_updates() so a subsequent save() failure cannot leave a
partially-mutated object in the storage cache.

Bug 3 (storage.py): add _cache_lock (threading.Lock) to
FileMemoryStorage and acquire it around every read/write of
_memory_cache, fixing concurrent-access races between the background
timer thread and HTTP reload calls.

Bug 4 (storage.py): replace in-place mutation
  memory_data["lastUpdated"] = ...
with a shallow copy
  memory_data = {**memory_data, "lastUpdated": ...}
so save() no longer silently modifies the caller's dict.

Regression tests added for all three bugs in test_memory_storage.py
and test_memory_updater.py.

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

* style: format test_memory_updater.py with ruff

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

* style: remove stale bug-number labels from code comments and docstrings

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

@@ -3,6 +3,7 @@
 import asyncio
 import atexit
 import concurrent.futures
+import copy
 import json
 import logging
 import math
@@ -380,7 +381,9 @@ class MemoryUpdater:
             response_text = "\n".join(lines[1:-1] if lines[-1] == "```" else lines[1:])
 
         update_data = json.loads(response_text)
-        updated_memory = self._apply_updates(current_memory, update_data, thread_id)
+        # Deep-copy before in-place mutation so a subsequent save() failure
+        # cannot corrupt the still-cached original object reference.
+        updated_memory = self._apply_updates(copy.deepcopy(current_memory), update_data, thread_id)
         updated_memory = _strip_upload_mentions_from_memory(updated_memory)
         return get_memory_storage().save(updated_memory, agent_name)