[Yatsuiii]

Description

When an executor enqueues its Task and raises before that Task is saved, _run_producer and the consumer both insert the same row through the shared TaskManager. With DatabaseTaskStore one insert fails, and the request either returns the SUBMITTED task as a success or raises IntegrityError instead of the executor's error.

This moves the failure write to EventConsumer, as suggested on the issue:

• _run_producer no longer saves the failure. It only enqueues the exception, as before.
• The consumer records the failure when it dequeues the exception, so FAILED is written after every event the executor enqueued before raising.
• _write_failed_status creates the fallback task through ensure_task_id, with the context id from _task_manager.context_id, only when no task exists, which keeps the case fix: persist early producer failure as FAILED with originating message #1106 fixed. FAILED is stamped with the failure time, so last_updated is set. The write goes through _handle_task_modification_event rather than _handle_task_event, so it still lands when the agent answered with a Message.

Visible differences from the old producer write:

• FAILED carries the time of the failure. The old write kept the previous status time, or none, which left last_updated NULL.
• The agent's last status message moves from status.message into history, as on any status update.
• When a resumed task fails, the follow-up user message is now recorded in history. The old write dropped it.

Three tests are added. One holds the store's insert of the agent's Task until the executor has raised, which is the window a database round trip leaves open. It fails on main with UNIQUE constraint failed: tasks.id and passes with this change. The other two check that a task which fails after reporting progress is stamped with the failure time, and that a follow-up answered with a Message still leaves the task FAILED.

Checks on current main (79a6f45), Python 3.10: the full suite passes with Postgres 18 behind the database tests (2396 passed, 92 skipped; the 4 cross-version tests timed out starting their servers in that run and pass on their own). I did not run the MySQL tests. ruff check, ruff format --check and ty check show nothing new.

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• Ensure the tests and linter pass
• Appropriate docs were updated (if necessary)

Fixes #1351

[github-actions]

🧪 Code Coverage (vs main)

⬇️ Download Full Report

	Base	PR	Delta
src/a2a/server/agent_execution/active_task.py	95.40%	95.46%	🟢 +0.07%
src/a2a/server/tasks/database_task_store.py	92.47%	95.16%	🟢 +2.69%
Total	92.90%	92.96%	🟢 +0.06%

Generated by coverage-comment.yml

[Iwaniukooo11]

LGTM