fix(memory): keep sessionless memories separate from a session named __unknown_session_id__

src/google/adk/memory/in_memory_memory_service.py

@@ -32,7 +32,6 @@
   from ..events.event import Event
   from ..sessions.session import Session
 
-_UNKNOWN_SESSION_ID = '__unknown_session_id__'
 _MAX_SEARCH_RESULTS = 10
 
 
@@ -86,9 +85,12 @@ class InMemoryMemoryService(BaseMemoryService):
   def __init__(self) -> None:
     self._lock = threading.Lock()
 
-    self._session_events: dict[tuple[str, str], dict[str, list[Event]]] = {}
+    self._session_events: dict[
+        tuple[str, str], dict[str | None, list[Event]]
+    ] = {}
     """Keys are (app_name, user_id). Values are dicts of session_id to
-    session event lists.
+    session event lists. Events added without a session ID are kept under the
+    None key, which no caller-provided session ID can alias.
     """
     self._deleted_memory_ids: dict[tuple[str, str], set[str]] = {}
     """Keys are (app_name, user_id). Values are sets of deleted memory_ids
@@ -122,7 +124,7 @@ async def add_events_to_memory(
   ) -> None:
     _ = custom_metadata
     user_key = _user_key(app_name, user_id)
-    scoped_session_id = session_id or _UNKNOWN_SESSION_ID
+    scoped_session_id = session_id or None
     events_to_add = [
         event for event in events if event.content and event.content.parts
     ]

tests/unittests/memory/test_in_memory_memory_service.py

@@ -160,6 +160,34 @@ async def test_add_events_to_memory_without_session_id_uses_default_bucket():
   assert unknown_session_events[0].id == 'event-1a'
 
 
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    'session_id', ['ordinary-session', '__unknown_session_id__']
+)
+async def test_add_session_to_memory_keeps_sessionless_memories(session_id):
+  """A session must not replace events added without a session ID."""
+  memory_service = InMemoryMemoryService()
+  await memory_service.add_events_to_memory(
+      app_name=MOCK_APP_NAME,
+      user_id=MOCK_USER_ID,
+      events=[MOCK_SESSION_1.events[0]],
+  )
+
+  await memory_service.add_session_to_memory(
+      Session(
+          app_name=MOCK_APP_NAME,
+          user_id=MOCK_USER_ID,
+          id=session_id,
+          last_update_time=1000,
+      )
+  )
+
+  result = await memory_service.search_memory(
+      app_name=MOCK_APP_NAME, user_id=MOCK_USER_ID, query='toolkit'
+  )
+  assert [memory.id for memory in result.memories] == ['event-1a']
+
+
 @pytest.mark.asyncio
 async def test_add_events_to_memory_alias_is_supported():
   """Tests that add_events_to_memory remains a compatibility alias."""