fix(live): treat input transcription as user message

During agent transfer, the input transcription is represented as user input. Also, the previous implementation is incorrect in that the LlmResponse could never have content.role == 'user'. Modified the docstring to match the behavior.

Co-authored-by: Liang Wu <wuliang@google.com>
PiperOrigin-RevId: 900980704

Author: wuliang229

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

@@ -720,19 +720,21 @@ async def _receive_from_model(
   ) -> AsyncGenerator[Event, None]:
     """Receive data from model and process events using BaseLlmConnection."""
 
-    def get_author_for_event(llm_response):
+    def get_author_for_event(llm_response: LlmResponse) -> str:
       """Get the author of the event.
 
-      When the model returns transcription, the author is "user". Otherwise, the
-      author is the agent name(not 'model').
+      When the model returns input transcription, the author is set to "user".
+      Otherwise, the author is the agent name (not 'model').
 
       Args:
         llm_response: The LLM response from the LLM call.
+
+      Returns:
+        The author of the event as a string, either "user" or the agent's name.
       """
-      if (
-          llm_response
-          and llm_response.content
-          and llm_response.content.role == 'user'
+      if llm_response and (
+          llm_response.input_transcription
+          or (llm_response.content and llm_response.content.role == 'user')
       ):
         return 'user'
       else:

tests/unittests/flows/llm_flows/test_base_llm_flow.py

@@ -925,3 +925,59 @@ async def test_postprocess_live_session_resumption_update():
   assert len(events) == 1
   assert events[0].live_session_resumption_update is not None
   assert events[0].live_session_resumption_update.new_handle == 'test_handle'
+
+
+@pytest.mark.asyncio
+async def test_receive_from_model_author_attribution():
+  """Test that _receive_from_model sets the correct author for events based on LlmResponse."""
+  agent = Agent(name='test_agent')
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent
+  )
+  flow = BaseLlmFlowForTesting()
+
+  mock_connection = mock.AsyncMock()
+
+  # Case 1: input_transcription is set -> author should be 'user'
+  response_1 = LlmResponse(
+      input_transcription=types.Transcription(text='test', finished=True)
+  )
+
+  # Case 2: default -> author should be agent.name
+  response_2 = LlmResponse(
+      content=types.Content(
+          role='model', parts=[types.Part.from_text(text='hello')]
+      )
+  )
+
+  # Case 3: content.role is 'user' -> author should be 'user'
+  response_3 = LlmResponse(
+      content=types.Content(
+          role='user', parts=[types.Part.from_text(text='user text')]
+      )
+  )
+
+  class StopTest(Exception):
+    pass
+
+  async def mock_receive():
+    yield response_1
+    yield response_2
+    yield response_3
+    raise StopTest()
+
+  mock_connection.receive = mock.Mock(side_effect=mock_receive)
+
+  events = []
+  try:
+    async for event in flow._receive_from_model(
+        mock_connection, 'event_id', invocation_context, LlmRequest()
+    ):
+      events.append(event)
+  except StopTest:
+    pass
+
+  assert len(events) == 3
+  assert events[0].author == 'user'
+  assert events[1].author == 'test_agent'
+  assert events[2].author == 'user'