[cchinchilla-dev]

Description

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Fixes #1421 🦕

Problem

Each EventQueueSource starts its dispatcher task when it is created, and ActiveTask creates two of them in __init__. When the setup in start() fails, because the stored task is in a terminal state or is missing, the except block re-raises without closing them:

except Exception:
    logger.debug('ActiveTask[%s]: Setup failed, cleaning up', self._task_id)
    self._is_finished.set()
    if self._reference_count == 0 and self._on_cleanup:
        self._on_cleanup(self)
    raise  # _event_queue_agent and _event_queue_subscribers stay open

A SendMessage to a completed task goes through this path, so every rejected request leaves two _dispatch_loop tasks pending until they are garbage collected and logged as Task was destroyed but it is pending!.

Fix

The except block in start() (src/a2a/server/agent_execution/active_task.py) now closes _event_queue_agent and _event_queue_subscribers with close(immediate=True) before calling _on_cleanup, the same way aclose() closes them. aclose() itself can't be used here because it takes _lock, which start() already holds.

The change only touches the failure path, so a successful start() is not affected.

Test

A test was added to the existing suite at tests/server/agent_execution/test_active_task.py:

• test_active_task_start_setup_failure_closes_event_queues: after start() fails on a completed task (UnsupportedOperationError) or a missing one (TaskNotFoundError), both dispatcher tasks are done.

Both cases fail on main with the dispatcher tasks still pending and pass with the fix. No existing test was modified or removed. Happy to adapt the test approach based on maintainer feedback.

[github-actions]

🧪 Code Coverage (vs main)

⬇️ Download Full Report

	Base	PR	Delta
src/a2a/server/agent_execution/active_task.py	96.10%	96.67%	🟢 +0.57%
Total	93.42%	93.45%	🟢 +0.03%

Generated by coverage-comment.yml