fix: persist early producer failure as FAILED with originating message

[AXEG0]

Fixes #1067

Summary

• seed the originating message into V2 ActiveTask TaskManager creation so newly created fallback tasks retain request history
• synchronously persist TASK_STATE_FAILED from _run_producer when producer setup/execution raises, so persistence does not depend on the closing event queue
• avoid appending the seeded originating message a second time when the first task update also carries it

Tests

• ./scripts/lint.sh
• uv run pytest tests/server/request_handlers/test_default_request_handler_v2.py::test_on_message_send_early_producer_exception_marks_task_failed tests/server/request_handlers/test_default_request_handler_v2.py::test_on_message_send_early_producer_exception_preserves_originating_message
• uv run pytest tests/server/request_handlers/test_default_request_handler_v2.py

[gemini-code-assist]

Code Review

This pull request ensures that early producer failures are persisted directly as failed tasks and that originating messages are preserved in the task history. It also adds corresponding unit tests. Feedback includes improving Protobuf message comparison by using message_id instead of direct equality, and directly assigning the task status state instead of using CopyFrom to avoid clearing other status fields.

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[github-actions]

🧪 Code Coverage (vs main)

⬇️ Download Full Report

	Base	PR	Delta
src/a2a/server/agent_execution/active_task.py	95.92%	95.99%	🟢 +0.07%
Total	92.99%	92.99%	⚪️ 0.00%

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