fix(eval): label a sub-agent's reply with its own name for the judge

src/google/adk/evaluation/llm_as_judge_utils.py

@@ -100,6 +100,38 @@ def get_text_from_content(
   return None
 
 
+def get_final_response_author(invocation: Invocation) -> Optional[str]:
+  """Returns the author of the event that carried the final response.
+
+  `EvaluationGenerator.convert_events_to_eval_invocations` keeps that event
+  among the invocation events and moves its content to `final_response`, so it
+  is the last agent event left without content. An event after it that has
+  content, such as a tool call another agent made later in the turn, is not
+  it.
+
+  An invocation that was put together some other way may have no such event,
+  and the last agent event is used instead.
+
+  Args:
+    invocation: The invocation whose final response is being attributed.
+
+  Returns:
+    The author, or None if the invocation has no agent events.
+  """
+  intermediate_data = invocation.intermediate_data
+  if not isinstance(intermediate_data, InvocationEvents):
+    return None
+  agent_events = [
+      event
+      for event in intermediate_data.invocation_events
+      if not (event.author and event.author.lower() == "user")
+  ]
+  for event in reversed(agent_events):
+    if not (event.content and event.content.parts):
+      return event.author
+  return agent_events[-1].author if agent_events else None
+
+
 def get_eval_status(score: Optional[float], threshold: float) -> EvalStatus:
   if score is None:
     return EvalStatus.NOT_EVALUATED

src/google/adk/evaluation/rubric_based_multi_turn_trajectory_evaluator.py

@@ -31,6 +31,7 @@
 from .evaluator import _validate_invocation_lengths
 from .evaluator import EvaluationResult
 from .evaluator import PerInvocationResult
+from .llm_as_judge_utils import get_final_response_author
 from .rubric_based_evaluator import RubricBasedEvaluator
 
 logger = logging.getLogger("google_adk." + __name__)
@@ -234,13 +235,7 @@ def _assemble_dialogue_history(
 
       # FINAL AGENT TURN
       if invocation.final_response and invocation.final_response.parts:
-        intermediate_data = invocation.intermediate_data
-        agent_name = "agent"
-        if (
-            isinstance(intermediate_data, InvocationEvents)
-            and intermediate_data.invocation_events
-        ):
-          agent_name = intermediate_data.invocation_events[0].author
+        agent_name = get_final_response_author(invocation) or "agent"
         role = f"AGENT ({agent_name})"
         text = extract_text_from_content(
             invocation.final_response, splitter=" "

tests/unittests/evaluation/test_llm_as_judge_utils.py

@@ -26,6 +26,7 @@
 from google.adk.evaluation.evaluator import EvalStatus
 from google.adk.evaluation.llm_as_judge_utils import get_average_rubric_score
 from google.adk.evaluation.llm_as_judge_utils import get_eval_status
+from google.adk.evaluation.llm_as_judge_utils import get_final_response_author
 from google.adk.evaluation.llm_as_judge_utils import get_grounding_metadata_as_json_str
 from google.adk.evaluation.llm_as_judge_utils import get_text_from_content
 from google.adk.evaluation.llm_as_judge_utils import get_tool_calls_and_responses_as_json_str
@@ -222,6 +223,111 @@ def test_get_text_from_content_skips_thought_parts_in_intermediate_responses():
   assert text == "Let me check.\nDone."
 
 
+def _make_invocation_with_reply(
+    intermediate_data: IntermediateData | InvocationEvents | None,
+) -> Invocation:
+  """Returns an invocation that has a final response."""
+  return Invocation(
+      user_content=genai_types.Content(
+          parts=[genai_types.Part(text="How much do I owe?")]
+      ),
+      final_response=genai_types.Content(
+          parts=[genai_types.Part(text="You owe $42.")]
+      ),
+      intermediate_data=intermediate_data,
+  )
+
+
+def _make_tool_call_event(author: str) -> InvocationEvent:
+  """Returns an event in which `author` calls a tool."""
+  return InvocationEvent(
+      author=author,
+      content=genai_types.Content(
+          parts=[
+              genai_types.Part(
+                  function_call=genai_types.FunctionCall(name="a_tool", args={})
+              )
+          ]
+      ),
+  )
+
+
+def test_get_final_response_author_after_transfer():
+  """The reply belongs to the sub-agent, not the agent that handed off."""
+  invocation = _make_invocation_with_reply(
+      InvocationEvents(
+          invocation_events=[
+              _make_tool_call_event("router"),
+              # `convert_events_to_eval_invocations` keeps the final
+              # response's event, with its content moved to `final_response`.
+              InvocationEvent(author="billing_agent"),
+          ]
+      )
+  )
+
+  assert get_final_response_author(invocation) == "billing_agent"
+
+
+@pytest.mark.parametrize(
+    "later_event",
+    [
+        InvocationEvent(
+            author="billing_agent",
+            usage_metadata=genai_types.GenerateContentResponseUsageMetadata(
+                total_token_count=12
+            ),
+        ),
+        _make_tool_call_event("audit_agent"),
+    ],
+    ids=["usage_report", "tool_call_of_another_agent"],
+)
+def test_get_final_response_author_with_later_event(later_event):
+  """An event after the reply's own event does not take the reply over."""
+  invocation = _make_invocation_with_reply(
+      InvocationEvents(
+          invocation_events=[
+              _make_tool_call_event("router"),
+              InvocationEvent(author="billing_agent"),
+              later_event,
+          ]
+      )
+  )
+
+  assert get_final_response_author(invocation) == "billing_agent"
+
+
+def test_get_final_response_author_without_event_for_the_reply():
+  """A hand-built invocation falls back to its last agent event."""
+  invocation = _make_invocation_with_reply(
+      InvocationEvents(
+          invocation_events=[
+              _make_tool_call_event("router"),
+              _make_tool_call_event("billing_agent"),
+              InvocationEvent(
+                  author="user",
+                  content=genai_types.Content(
+                      parts=[genai_types.Part(text="Thanks.")]
+                  ),
+              ),
+          ]
+      )
+  )
+
+  assert get_final_response_author(invocation) == "billing_agent"
+
+
+@pytest.mark.parametrize(
+    "intermediate_data",
+    [None, IntermediateData(), InvocationEvents(invocation_events=[])],
+    ids=["no_intermediate_data", "legacy_intermediate_data", "no_events"],
+)
+def test_get_final_response_author_without_agent_events(intermediate_data):
+  """There is no author to report when the invocation has no agent events."""
+  invocation = _make_invocation_with_reply(intermediate_data)
+
+  assert get_final_response_author(invocation) is None
+
+
 def test_get_eval_status_with_none_score():
   """Tests get_eval_status returns NOT_EVALUATED for a None score."""
   assert get_eval_status(score=None, threshold=0.5) == EvalStatus.NOT_EVALUATED

tests/unittests/evaluation/test_rubric_based_multi_turn_trajectory_evaluator.py

@@ -378,6 +378,52 @@ async def test_invocation_without_user_content(self, evaluator):
         "AGENT (agent) TURN 1: Agent response." in evaluator._formatted_dialogue
     )
 
+  def test_final_reply_is_attributed_to_the_agent_that_wrote_it(
+      self, evaluator
+  ):
+    """After a transfer, the reply is labelled with the sub-agent's name."""
+    transfer_call = genai_types.Part(
+        function_call=genai_types.FunctionCall(
+            name="transfer_to_agent", args={"agent_name": "billing_agent"}
+        )
+    )
+    transfer_response = genai_types.Part(
+        function_response=genai_types.FunctionResponse(
+            name="transfer_to_agent", response={"result": None}
+        )
+    )
+    invocation = _make_invocation(
+        user_text="How much do I owe?",
+        agent_text="You owe $42.",
+        intermediate_data=InvocationEvents(
+            invocation_events=[
+                InvocationEvent(
+                    author="router",
+                    content=genai_types.Content(parts=[transfer_call]),
+                ),
+                InvocationEvent(
+                    author="router",
+                    content=genai_types.Content(parts=[transfer_response]),
+                ),
+                # `convert_events_to_eval_invocations` keeps the final
+                # response's event, with its content moved to
+                # `final_response`.
+                InvocationEvent(author="billing_agent"),
+            ]
+        ),
+    )
+
+    evaluator._assemble_dialogue_history([invocation])
+
+    assert evaluator._formatted_dialogue == (
+        "USER TURN 1: How much do I owe?\n"
+        "AGENT (router) TURN 1 (tool call):"
+        ' transfer_to_agent({"agent_name": "billing_agent"})\n'
+        "AGENT (router) TURN 1 (tool output):"
+        ' transfer_to_agent -> {"result": null}\n'
+        "AGENT (billing_agent) TURN 1: You owe $42."
+    )
+
   def test_thought_parts_are_left_out_of_dialogue(self, evaluator):
     """Agent thought parts are left out of the judge's dialogue."""
     invocation = Invocation(