fix: accumulate list values when merging parallel tool call state_delta

Parallel tool calls writing list values to the same state_delta key
were silently dropped because deep_merge_dicts only recursed into
dict values; lists hit the overwrite branch.

Closes #5190

Co-authored-by: George Weale <gweale@google.com>
PiperOrigin-RevId: 905300264

Author: GWeale

src/google/adk/flows/llm_flows/functions.py

@@ -1143,12 +1143,10 @@ def __build_response_event(
 
 
 def deep_merge_dicts(d1: dict, d2: dict) -> dict:
-  """Recursively merges d2 into d1; concatenates list values at the same key."""
+  """Recursively merges d2 into d1."""
   for key, value in d2.items():
     if key in d1 and isinstance(d1[key], dict) and isinstance(value, dict):
       d1[key] = deep_merge_dicts(d1[key], value)
-    elif key in d1 and isinstance(d1[key], list) and isinstance(value, list):
-      d1[key] = d1[key] + value
     else:
       d1[key] = value
   return d1

tests/unittests/flows/llm_flows/test_functions_simple.py

@@ -20,7 +20,6 @@
 from google.adk.events.event import Event
 from google.adk.events.event_actions import EventActions
 from google.adk.events.ui_widget import UiWidget
-from google.adk.flows.llm_flows.functions import deep_merge_dicts
 from google.adk.flows.llm_flows.functions import find_matching_function_call
 from google.adk.flows.llm_flows.functions import handle_function_calls_async
 from google.adk.flows.llm_flows.functions import handle_function_calls_live
@@ -1237,62 +1236,3 @@ async def mock_run(*args, **kwargs):
   # Verify the image was converted to a blob
   assert len(response_part.parts) == 1
   assert response_part.parts[0].inline_data is not None
-
-
-def test_deep_merge_dicts_concatenates_lists_at_same_key():
-  d1 = {'items': ['a', 'b']}
-  d2 = {'items': ['c', 'd']}
-  assert deep_merge_dicts(d1, d2) == {'items': ['a', 'b', 'c', 'd']}
-
-
-def test_deep_merge_dicts_concatenates_nested_lists():
-  d1 = {'state_delta': {'items': ['a']}}
-  d2 = {'state_delta': {'items': ['b']}}
-  assert deep_merge_dicts(d1, d2) == {'state_delta': {'items': ['a', 'b']}}
-
-
-def test_deep_merge_dicts_overwrites_when_types_differ():
-  d1 = {'x': ['a']}
-  d2 = {'x': 'b'}
-  assert deep_merge_dicts(d1, d2) == {'x': 'b'}
-
-  d1 = {'x': 'a'}
-  d2 = {'x': ['b']}
-  assert deep_merge_dicts(d1, d2) == {'x': ['b']}
-
-
-def test_deep_merge_dicts_overwrites_scalars():
-  d1 = {'x': 1, 'y': 'old'}
-  d2 = {'x': 2, 'y': 'new'}
-  assert deep_merge_dicts(d1, d2) == {'x': 2, 'y': 'new'}
-
-
-def test_merge_parallel_function_response_events_concatenates_state_delta_lists():
-  """Regression test for https://github.com/google/adk-python/issues/5190."""
-  function_response1 = types.FunctionResponse(
-      id='func_1', name='append_item', response={'result': 'ok'}
-  )
-  function_response2 = types.FunctionResponse(
-      id='func_2', name='append_item', response={'result': 'ok'}
-  )
-
-  event1 = Event(
-      invocation_id='inv_1',
-      author='test_agent',
-      content=types.Content(
-          role='user', parts=[types.Part(function_response=function_response1)]
-      ),
-      actions=EventActions(state_delta={'items': ['a']}),
-  )
-  event2 = Event(
-      invocation_id='inv_1',
-      author='test_agent',
-      content=types.Content(
-          role='user', parts=[types.Part(function_response=function_response2)]
-      ),
-      actions=EventActions(state_delta={'items': ['b']}),
-  )
-
-  merged_event = merge_parallel_function_response_events([event1, event2])
-
-  assert merged_event.actions.state_delta == {'items': ['a', 'b']}