feat(server): release parked interrupted tasks after a configurable timeout

[christophstach]

Description

Second half of #1296, following the direction agreed in #1296 (comment) and the maintainer's reply.

A task in input-required or auth-required keeps its ActiveTask (producer, consumer, two dispatchers, registry entry) until a follow-up arrives, which may never happen.

Change

• New DefaultRequestHandlerV2(..., interrupted_task_timeout: float | None = None). The default None keeps today's behavior.
• When the timeout is set, ActiveTask starts a timer once a request finishes or the last subscriber leaves. A new request or subscriber cancels it. When it fires, the ActiveTask is released only if all of these still hold:
  • the task is in an interrupted state,
  • no request is running or queued,
  • no subscriber is attached.
• The stored task is not modified. A follow-up recreates the ActiveTask from the store.
• 0 releases as soon as the task is idle.

Registry fix

Removing a finished ActiveTask from the registry runs asynchronously. A follow-up that arrived in between was rejected with Task … is already completed. get_or_create now replaces a finished entry, and the scheduled removal only deletes the instance it was scheduled for. Side effect without a timeout: a follow-up to a task that just ended now gets is in terminal state: …, the same error as outside that window.

Tests

Seven new tests in test_default_request_handler_v2.py:

• no timeout by default,
• release for input-required and auth-required, with no leftover asyncio tasks and the stored state unchanged,
• resume from the store after a release,
• reset by a follow-up,
• reset by a subscriber,
• no release while the executor is still running,
• a follow-up to a finished but still registered ActiveTask (this one fails on main).

Checks

• ./scripts/lint.sh: passed (the 3 ty warnings already exist on main).
• uv run pytest: 2285 passed. The new tests passed 10/10 repeated runs and also pass on Python 3.14.
• Not tested: cluster mode (event_stream).

Part of #1296

[github-actions]

🧪 Code Coverage (vs main)

⬇️ Download Full Report

	Base	PR	Delta
src/a2a/server/agent_execution/active_task.py	95.14%	95.46%	🟢 +0.33%
src/a2a/server/agent_execution/active_task_registry.py	97.37%	97.65%	🟢 +0.28%
src/a2a/server/cluster/database_event_stream.py	96.94%	92.86%	🔴 -4.08%
Total	93.16%	93.15%	🔴 -0.01%

Generated by coverage-comment.yml