feat: expose live_session_resumption_update in events for cross-connection resumption

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

@@ -738,17 +738,14 @@ def get_author_for_event(llm_response):
       else:
         return invocation_context.agent.name
 
+
     while True:
       async with Aclosing(llm_connection.receive()) as agen:
         async for llm_response in agen:
-          if llm_response.live_session_resumption_update:
-            logger.info(
-                'Update session resumption handle:'
-                f' {llm_response.live_session_resumption_update}.'
-            )
-            invocation_context.live_session_resumption_handle = (
-                llm_response.live_session_resumption_update.new_handle
-            )
+          model_response_event = Event(
+              id=Event.new_id(),
+              invocation_id=invocation_context.invocation_id,
+              author=get_author_for_event(llm_response),
           if llm_response.go_away:
             logger.info(f'Received go away signal: {llm_response.go_away}')
             # The server signals that it will close the connection soon.
@@ -1009,6 +1006,25 @@ async def _postprocess_live(
       async for event in agen:
         yield event
 
+    # Handle session resumption updates for cross-connection resumption.
+    # Must be before skip condition - resumption updates have no content.
+    if llm_response.live_session_resumption_update:
+      # Update internal handle for auto-resumption within run_live()
+      logger.info(
+          'Update session resumption handle: %s',
+          llm_response.live_session_resumption_update,
+      )
+      invocation_context.live_session_resumption_handle = (
+          llm_response.live_session_resumption_update.new_handle
+      )
+
+      # Expose update in event for application-level cross-connection resumption
+      model_response_event.live_session_resumption_update = (
+          llm_response.live_session_resumption_update
+      )
+      yield model_response_event
+      return
+
     # Skip the model response event if there is no content and no error code.
     # This is needed for the code executor to trigger another loop.
     # But don't skip control events like turn_complete or transcription events.

tests/unittests/flows/llm_flows/test_base_llm_flow_session_resumption.py

@@ -0,0 +1,114 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from google.adk.agents.llm_agent import Agent
+from google.adk.events.event import Event
+from google.adk.flows.llm_flows.base_llm_flow import BaseLlmFlow
+from google.adk.models.llm_request import LlmRequest
+from google.adk.models.llm_response import LlmResponse
+from google.genai import types
+import pytest
+
+from ... import testing_utils
+
+
+class BaseLlmFlowForTesting(BaseLlmFlow):
+  """Test implementation of BaseLlmFlow for testing purposes."""
+
+  pass
+
+
+@pytest.mark.asyncio
+async def test_postprocess_live_yields_session_resumption_event():
+  """Test _postprocess_live yields event for session resumption update."""
+  # Create a resumption update as received from Gemini Live API
+  resumption_update = types.LiveServerSessionResumptionUpdate(
+      new_handle='test-handle-abc123',
+      resumable=True,
+  )
+
+  # Create LlmResponse with only a resumption update (no content)
+  llm_response = LlmResponse(live_session_resumption_update=resumption_update)
+
+  # Set up invocation context
+  agent = Agent(name='test_agent', model='mock')
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent, user_content=''
+  )
+
+  # Create the mutable event that _postprocess_live populates
+  model_response_event = Event(
+      id=Event.new_id(),
+      invocation_id=invocation_context.invocation_id,
+      author=agent.name,
+  )
+
+  flow = BaseLlmFlowForTesting()
+  llm_request = LlmRequest()
+  events = []
+
+  # Collect events from _postprocess_live
+  async for event in flow._postprocess_live(
+      invocation_context, llm_request, llm_response, model_response_event
+  ):
+    events.append(event)
+
+  # Verify event is yielded with resumption update
+  assert len(events) == 1
+  assert events[0].live_session_resumption_update == resumption_update
+  assert (
+      events[0].live_session_resumption_update.new_handle
+      == 'test-handle-abc123'
+  )
+  assert events[0].live_session_resumption_update.resumable is True
+
+  # Verify invocation context handle is updated for auto-resumption
+  assert (
+      invocation_context.live_session_resumption_handle == 'test-handle-abc123'
+  )
+
+
+@pytest.mark.asyncio
+async def test_postprocess_live_skips_empty_response():
+  """Test _postprocess_live skips response with no content or resumption."""
+  # Create LlmResponse with no content and no resumption update
+  llm_response = LlmResponse()
+
+  # Set up invocation context
+  agent = Agent(name='test_agent', model='mock')
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent, user_content=''
+  )
+
+  model_response_event = Event(
+      id=Event.new_id(),
+      invocation_id=invocation_context.invocation_id,
+      author=agent.name,
+  )
+
+  flow = BaseLlmFlowForTesting()
+  llm_request = LlmRequest()
+  events = []
+
+  # Collect events from _postprocess_live
+  async for event in flow._postprocess_live(
+      invocation_context, llm_request, llm_response, model_response_event
+  ):
+    events.append(event)
+
+  # Verify no event is yielded for empty response
+  assert len(events) == 0
+
+  # Verify handle remains unset
+  assert invocation_context.live_session_resumption_handle is None