fix: Using base event's invocation id when merge multiple function response event

fix #1531

PiperOrigin-RevId: 795638800

Author: seanzhougoogle

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

@@ -682,7 +682,7 @@ def merge_parallel_function_response_events(
 
   # Create the new merged event
   merged_event = Event(
-      invocation_id=Event.new_id(),
+      invocation_id=base_event.invocation_id,
       author=base_event.author,
       branch=base_event.branch,
       content=types.Content(role='user', parts=merged_parts),

tests/unittests/flows/llm_flows/test_functions_simple.py

@@ -19,6 +19,7 @@
 from google.adk.agents.llm_agent import Agent
 from google.adk.events.event import Event
 from google.adk.flows.llm_flows.functions import find_matching_function_call
+from google.adk.flows.llm_flows.functions import merge_parallel_function_response_events
 from google.adk.tools.function_tool import FunctionTool
 from google.adk.tools.tool_context import ToolContext
 from google.genai import types
@@ -931,6 +932,119 @@ async def yielding_async_function() -> dict:
   assert execution_order == ['non_yield_A', 'non_yield_B', 'yield_C', 'yield_D']
 
 
+def test_merge_parallel_function_response_events_preserves_invocation_id():
+  """Test that merge_parallel_function_response_events preserves the base event's invocation_id."""
+  # Create multiple function response events with different invocation IDs
+  invocation_id = "base_invocation_123"
+  
+  function_response1 = types.FunctionResponse(
+      id="func_123", name="test_function1", response={"result": "success1"}
+  )
+  
+  function_response2 = types.FunctionResponse(
+      id="func_456", name="test_function2", response={"result": "success2"}
+  )
+  
+  event1 = Event(
+      invocation_id=invocation_id,
+      author="test_agent",
+      content=types.Content(
+          role="user", parts=[types.Part(function_response=function_response1)]
+      ),
+  )
+  
+  event2 = Event(
+      invocation_id="different_invocation_456",  # Different invocation ID
+      author="test_agent", 
+      content=types.Content(
+          role="user", parts=[types.Part(function_response=function_response2)]
+      ),
+  )
+  
+  # Merge the events
+  merged_event = merge_parallel_function_response_events([event1, event2])
+  
+  # Should preserve the base event's (first event's) invocation_id
+  assert merged_event.invocation_id == invocation_id
+  assert merged_event.invocation_id != "different_invocation_456"
+  
+  # Should contain both function responses
+  assert len(merged_event.content.parts) == 2
+  
+  # Verify the responses are preserved
+  response_ids = {part.function_response.id for part in merged_event.content.parts}
+  assert "func_123" in response_ids
+  assert "func_456" in response_ids
+
+
+def test_merge_parallel_function_response_events_single_event():
+  """Test that merge_parallel_function_response_events returns single event unchanged."""
+  invocation_id = "single_invocation_123"
+  
+  function_response = types.FunctionResponse(
+      id="func_123", name="test_function", response={"result": "success"}
+  )
+  
+  event = Event(
+      invocation_id=invocation_id,
+      author="test_agent",
+      content=types.Content(
+          role="user", parts=[types.Part(function_response=function_response)]
+      ),
+  )
+  
+  # Merge single event
+  merged_event = merge_parallel_function_response_events([event])
+  
+  # Should return the same event object
+  assert merged_event is event
+  assert merged_event.invocation_id == invocation_id
+
+
+def test_merge_parallel_function_response_events_preserves_other_attributes():
+  """Test that merge_parallel_function_response_events preserves other attributes from base event."""
+  invocation_id = "base_invocation_123"
+  base_author = "base_agent"
+  base_branch = "main_branch"
+  
+  function_response1 = types.FunctionResponse(
+      id="func_123", name="test_function1", response={"result": "success1"}
+  )
+  
+  function_response2 = types.FunctionResponse(
+      id="func_456", name="test_function2", response={"result": "success2"}
+  )
+  
+  event1 = Event(
+      invocation_id=invocation_id,
+      author=base_author,
+      branch=base_branch,
+      content=types.Content(
+          role="user", parts=[types.Part(function_response=function_response1)]
+      ),
+  )
+  
+  event2 = Event(
+      invocation_id="different_invocation_456",
+      author="different_agent",  # Different author
+      branch="different_branch", # Different branch
+      content=types.Content(
+          role="user", parts=[types.Part(function_response=function_response2)]
+      ),
+  )
+  
+  # Merge the events
+  merged_event = merge_parallel_function_response_events([event1, event2])
+  
+  # Should preserve base event's attributes
+  assert merged_event.invocation_id == invocation_id
+  assert merged_event.author == base_author
+  assert merged_event.branch == base_branch
+  
+  # Should contain both function responses
+  assert len(merged_event.content.parts) == 2
+
+
 @pytest.mark.asyncio
 async def test_yielding_async_functions_run_concurrently():
   """Test that async functions with proper yields run concurrently."""