chore: Send user message to the agent that returned a corresponding function call if user message is a function response

PiperOrigin-RevId: 773895971

src/google/adk/runners.py

@@ -337,6 +337,8 @@ class Runner:
     """Finds the agent to run to continue the session.
 
     A qualified agent must be either of:
+    - The agent that returned a function call and the last user message is a
+      function response to this function call.
     - The root agent;
     - An LlmAgent who replied last and is capable to transfer to any other agent
       in the agent hierarchy.
@@ -348,6 +350,15 @@ class Runner:
     Returns:
       The agent of the last message in the session or the root agent.
     """
+    # If the last event is a function response, should send this response to
+    # the agent that returned the corressponding function call regardless the
+    # type of the agent. e.g. a remote a2a agent may surface a credential
+    # request as a special long running function tool call.
+    event = _find_function_call_event_if_last_event_is_function_response(
+        session
+    )
+    if event and event.author:
+      return root_agent.find_agent(event.author)
     for event in filter(lambda e: e.author != 'user', reversed(session.events)):
       if event.author == root_agent.name:
         # Found root agent.
@@ -527,3 +538,35 @@ class InMemoryRunner(Runner):
         session_service=self._in_memory_session_service,
         memory_service=InMemoryMemoryService(),
     )
+
+
+def _find_function_call_event_if_last_event_is_function_response(
+    session: Session,
+) -> Optional[Event]:
+  events = session.events
+  if not events:
+    return None
+
+  last_event = events[-1]
+  if (
+      last_event.content
+      and last_event.content.parts
+      and any(part.function_response for part in last_event.content.parts)
+  ):
+
+    function_call_id = next(
+        part.function_response.id
+        for part in last_event.content.parts
+        if part.function_response
+    )
+    for i in range(len(events) - 2, -1, -1):
+      event = events[i]
+      # looking for the system long running request euc function call
+      function_calls = event.get_function_calls()
+      if not function_calls:
+        continue
+
+      for function_call in function_calls:
+        if function_call.id == function_call_id:
+          return event
+  return None