feat: expose live_session_resumption_update in events for cross-connection resumption

[AshleyMaloney]

Fixes #4357

Summary

Expose live_session_resumption_update in events so applications can implement cross-WebSocket-connection session resumption for Gemini Live API voice assistants.

Problem

When building voice assistants with run_live(), ADK receives session resumption handles from Gemini and stores them internally, but never exposes them to applications. This prevents implementing conversation continuity when users:

• Switch networks (WiFi → cellular)
• Refresh browser tabs
• Background mobile apps briefly
• Experience brief connectivity drops

Solution

Add a handler for live_session_resumption_update before the skip condition in _postprocess_live, following the same pattern used for transcription events.

# 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:
  model_response_event.live_session_resumption_update = (
      llm_response.live_session_resumption_update
  )
  yield model_response_event
  return

Usage

async for event in runner.run_live(user_id, session_id, queue, run_config):
    # Capture handle when received
    if event.live_session_resumption_update:
        handle = event.live_session_resumption_update.new_handle
        await persist_to_session_state(session_id, handle)

# On reconnection, pass the saved handle
run_config = RunConfig(
    session_resumption=types.SessionResumptionConfig(handle=saved_handle)
)

Testing

• Tested locally with production voice assistant
• Verified resumption handles are yielded in events
• Verified cross-connection resumption works with persisted handles

Happy to add unit tests or documentation updates if requested.

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[gemini-code-assist]

Summary of Changes

Hello @AshleyMaloney, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the robustness of Gemini Live API voice assistants by exposing live_session_resumption_update events. This allows client applications to capture and utilize session resumption handles, thereby enabling seamless conversation continuity even when underlying WebSocket connections are interrupted due to network changes, application state shifts, or brief disconnections. The change addresses a critical limitation where these handles were previously internal, leading to a more resilient and user-friendly voice assistant experience.

Highlights

• Session Resumption Event Exposure: The live_session_resumption_update event is now exposed in the Gemini Live API, allowing applications to access session resumption handles.
• Enhanced Conversation Continuity: This change enables the implementation of cross-WebSocket-connection session resumption, improving conversation continuity for voice assistants during network changes, browser refreshes, or app backgrounding.
• New Handler in _postprocess_live: A new conditional block has been added to the _postprocess_live asynchronous generator to detect and yield live_session_resumption_update events before the general skip condition.

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Changelog

• src/google/adk/flows/llm_flows/base_llm_flow.py
  • Added a new conditional block to the _postprocess_live function to check for llm_response.live_session_resumption_update.
  • Ensured that live_session_resumption_update events are yielded as model_response_event before the existing skip condition, as these updates have no content but are crucial for resumption.

Activity

• The author has addressed and fixed issue [Gemini Live API] Expose live_session_resumption_update in Events for cross-connection session resumption #4357.
• Local testing has been conducted with a production voice assistant to verify the changes.
• Verification confirms that resumption handles are correctly yielded in events.
• Cross-connection resumption has been verified to work successfully with persisted handles.
• The author has offered to add unit tests or documentation updates if deemed necessary by reviewers.

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[gemini-code-assist]

Code Review

This pull request adds a useful feature to expose live_session_resumption_update in events, enabling applications to implement cross-connection session resumption. The implementation correctly places the new logic in _postprocess_live to handle these updates. I've suggested a small refactoring to centralize all logic related to session resumption updates within _postprocess_live for better code clarity and consistency. Overall, this is a solid contribution.