feat: add add_events_to_memory facade for event-delta

Adds BaseMemoryService.add_events_to_memory(session, events=..., custom_metadata=...) and CallbackContext.add_events_to_memory(events=..., custom_metadata=...) so callers can add memories from an explicit subset of ADK events.

Co-authored-by: George Weale <gweale@google.com>
PiperOrigin-RevId: 868261578

tests/unittests/agents/test_callback_context.py

@@ -373,6 +373,46 @@ class TestCallbackContextAddSessionToMemory:
       await context.add_session_to_memory()
 
 
+class TestCallbackContextAddEventsToMemory:
+  """Tests add_events_to_memory in CallbackContext."""
+
+  @pytest.mark.asyncio
+  async def test_add_events_to_memory_success(self, mock_invocation_context):
+    """Tests that add_events_to_memory calls the memory service correctly."""
+    memory_service = AsyncMock()
+    mock_invocation_context.memory_service = memory_service
+    test_event = MagicMock()
+
+    context = CallbackContext(mock_invocation_context)
+    await context.add_events_to_memory(
+        events=[test_event],
+        custom_metadata={"ttl": "6000s"},
+    )
+
+    memory_service.add_events_to_memory.assert_called_once_with(
+        app_name=mock_invocation_context.session.app_name,
+        user_id=mock_invocation_context.session.user_id,
+        session_id=mock_invocation_context.session.id,
+        events=[test_event],
+        custom_metadata={"ttl": "6000s"},
+    )
+
+  @pytest.mark.asyncio
+  async def test_add_events_to_memory_no_service_raises(
+      self, mock_invocation_context
+  ):
+    """Tests that add_events_to_memory raises ValueError with no service."""
+    mock_invocation_context.memory_service = None
+
+    context = CallbackContext(mock_invocation_context)
+
+    with pytest.raises(
+        ValueError,
+        match=r"Cannot add events to memory: memory service is not available\.",
+    ):
+      await context.add_events_to_memory(events=[MagicMock()])
+
+
 class TestToolContextAddSessionToMemory:
   """Test the add_session_to_memory method in ToolContext."""