Python: fix A2A status message ids

[he-yufeng]

Summary

• preserve the A2A status message ID when a streaming TaskStatusUpdateEvent is converted to AgentResponseUpdate
• preserve the same ID for in-progress task status messages surfaced from Task payloads
• add regression coverage for both status-event and in-progress-task streaming paths

Fixes #5949.

Validation

• uv run pytest tests\test_a2a_agent.py -q -k "streaming_working_update_user_role_mapping or streaming_status_update_event_yields_content"
• uv run ruff check agent_framework_a2a\_agent.py tests\test_a2a_agent.py
• uv run ruff format --check agent_framework_a2a\_agent.py tests\test_a2a_agent.py
• python -m py_compile python\packages\a2a\agent_framework_a2a\_agent.py python\packages\a2a\tests\test_a2a_agent.py
• git diff --check upstream/main..HEAD

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Fixes A2A status message IDs not being preserved when streaming events are converted to AgentResponseUpdate, so downstream consumers can correlate updates to their originating A2A message.

Changes:

• Propagate message_id from TaskStatus.message in _updates_from_task.
• Propagate message_id from TaskStatusUpdateEvent.status.message in _updates_from_task_update_event.
• Add regression tests asserting message_id is preserved on streaming updates.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
python/packages/a2a/agent_framework_a2a/_agent.py	Forwards the A2A message ID to AgentResponseUpdate in both task and status-update conversion paths.
python/packages/a2a/tests/test_a2a_agent.py	Updates existing test to use an explicit message ID and adds assertions verifying message_id propagation.

[he-yufeng]

Updated to address the inline comment and rebased on current main. Local validation: targeted A2A tests for the affected streaming paths passed, plus ruff check/format, py_compile, and git diff --check.