Cancel Temporal timer when workflow.sleep() task is cancelled

[carlosa54]

What was changed

When workflow.sleep() is wrapped in an asyncio.Task and that task is cancelled, two things now happen correctly:

1. The timer callback guards against calling set_result() on an already-cancelled future, preventing asyncio.InvalidStateError
2. A done_callback on the future propagates cancellation to the underlying Temporal timer via timer_handle.cancel(), which sends a cancel_timer command to the server

Previously, workflow.sleep() discarded the _TimerHandle returned by _timer_impl(), so there was no way to cancel the Temporal timer when the awaiting task was cancelled. This is in contrast to asyncio.sleep(), which goes through the event loop's call_later() path where Python's asyncio internals call handle.cancel() automatically

A new test (test_workflow_sleep_task_cancellation) mirrors the existing CancelSignalAndTimerFiredInSameTaskWorkflow test but uses workflow.sleep() instead of asyncio.sleep().

Why?

workflow.sleep() and asyncio.sleep() should behave the same way when cancelled.

Without this fix:

• An asyncio.InvalidStateError is logged when the timer fires after the task is already cancelled.
• The Temporal timer is never cancelled on the server (no TimerCanceled event in history), leaking server-side resources.

See Issues #782 and #1351 for the bug reports

Checklist

1. Closes [Bug] cancelled timer callback causes asyncio.exceptions.InvalidStateError #782

2. Closes [Bug] workflow.sleep() timer not canceled when wrapping asyncio.Task is canceled #1351

3. How was this tested:

• Added test_workflow_sleep_task_cancellation which starts a workflow.sleep(60 * 60) in a task, cancels it via signal, and asserts the workflow completes with "timer_cancelled" (no InvalidStateError)
• Verified existing timer cancellation tests still pass: test_workflow_cancel_multi, test_workflow_cancel_signal_and_timer_fired_in_same_task, test_workflow_sleep, test_concurrent_sleeps_use_proper_options

Also tested locally:

Before

After

4. Any docs updates needed? No

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