feat: a2a async updates

[greysonlalonde]

Note

Introduces configurable async update mechanisms for A2A delegation and refactors execution to a handler-based architecture.

• Adds StreamingConfig, PollingConfig, PushNotificationConfig and handlers; wire via A2AConfig.updates (default StreamingConfig) and utils.get_handler
• Extracts shared task processing into a2a/task_helpers.py and defines A2APollingTimeoutError
• Emits new A2A events (A2APollingStartedEvent, A2APollingStatusEvent, A2APushNotification*) and renders polling status in console formatter; registers listeners in event_listener.py
• Enhances A2A wrapper prompts with REMOTE_AGENT_COMPLETED_NOTICE and adjusts flow to respect trust_remote_completion_status and terminal TaskState
• Updates client creation to support polling and push notification configs; exports new APIs in a2a/__init__.py
• Improves executor handling when response_model is set (validate JSON before parsing)
• Documents update mechanisms in docs/en/learn/a2a-agent-delegation.mdx; adds integration tests and VCR cassettes; filters new x-a2a-* headers in tests

^{Written by Cursor Bugbot for commit 2deddb8. This will update automatically on new commits. Configure here.}

[cursor]

This is the final PR Bugbot will review for you during this billing cycle

Your free Bugbot reviews will reset on January 28

Details

Your team is on the Bugbot Free tier. On this plan, Bugbot will review limited PRs each billing cycle for each member of your team.

To receive Bugbot reviews on all of your PRs, visit the Cursor dashboard to activate Pro and start your 14-day free trial.

[lorenzejay]

lgtm