fix(memory): don't gate memory-update parse on optional factsToRemove key (#4075)

The parse gate required all of {user, history, newFacts, factsToRemove} to
be present before accepting the model's JSON. A well-formed update that
simply has no facts to remove (the common case) omits the empty
factsToRemove key and was silently rejected. Drop factsToRemove from the
required set so those updates parse and apply.

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

@@ -323,7 +323,7 @@ def _extract_text(content: Any) -> str:
     return str(content)
 
 
-_REQUIRED_MEMORY_UPDATE_TOP_LEVEL_KEYS = frozenset({"user", "history", "newFacts", "factsToRemove"})
+_REQUIRED_MEMORY_UPDATE_TOP_LEVEL_KEYS = frozenset({"user", "history", "newFacts"})
 
 
 def _normalize_memory_update_fact(fact: Any) -> dict[str, Any] | None:

backend/tests/test_memory_updater.py

@@ -6,6 +6,7 @@ from deerflow.agents.memory.prompt import format_conversation_for_update
 from deerflow.agents.memory.updater import (
     MemoryUpdater,
     _extract_text,
+    _parse_memory_update_response,
     clear_memory_data,
     create_memory_fact,
     create_memory_fact_with_created_fact,
@@ -1443,3 +1444,32 @@ class TestSyncUpdateBindsTraceContextVar:
 
             assert captured == ["inner-trace"]
             assert get_current_trace_id() == "outer-trace"
+
+
+class TestParseMemoryUpdateFactsToRemoveGate:
+    """``factsToRemove`` is optional in the memory-update JSON acceptance gate.
+
+    When there is nothing to remove, a well-behaved model omits ``factsToRemove``
+    entirely. The parser must still accept such an update (keeping ``newFacts``
+    intact) while continuing to reject unrelated JSON that lacks the load-bearing
+    ``history`` + ``newFacts`` keys.
+    """
+
+    def test_accepts_update_without_facts_to_remove(self):
+        text = '{"user": {}, "history": {}, "newFacts": [{"content": "User likes Rust", "category": "preference", "confidence": 0.9}]}'
+
+        parsed = _parse_memory_update_response(text)
+
+        assert isinstance(parsed, dict)
+        assert any(fact.get("content") == "User likes Rust" for fact in parsed.get("newFacts", []))
+
+    def test_still_rejects_decoy_object_missing_history_and_new_facts(self):
+        import json
+
+        # ``{"user": "alice"}`` has only the ``user`` key — missing history+newFacts,
+        # so it must never be mistaken for a memory update.
+        try:
+            _parse_memory_update_response('{"user": "alice"}')
+        except json.JSONDecodeError:
+            return
+        raise AssertionError('decoy object {"user": "alice"} must be rejected')