[VegetarianOrc]

Summary

Add workflow.TaskGroup for Python 3.11+ to make cancellation of mixed Temporal operations deterministic.

• Reuse the standard-library task-group state machine, replacing its private task registry with a dictionary-backed ordered collection.
• Request cancellation in task-addition order, without promising cleanup completion order.
• Export the API with a clear Python 3.10 construction error, recommend it in the sandbox warning and README, and combine the release notes.
• Cover registry ordering, cancellation/cleanup, nesting, and mixed timer/activity/child-workflow history ordering and replay with caching enabled and disabled.

Fixes #2069. Stacked on #2085.

Compatibility notes

The implementation depends on the private asyncio _tasks registry, audited across CPython 3.11–3.14. It inherits the running interpreter cancellation semantics, including older Python limitations, subject to existing workflow event-loop restrictions; eager task start is not supported. Previously recorded nondeterministic histories are not repaired.

Validation

Final revision on Python 3.13.7:

• poe test -s tests/test_workflow_task_group.py tests/test_workflow_exports.py tests/worker/workflow_sandbox/test_runner.py — 27 passed.
• poe lint — passed, including pyright, mypy, and basedpyright.
• git diff --check — passed.

An earlier, broader test revision also passed on Python 3.10.18, 3.11.8, 3.12.13, 3.13.7, and 3.14.2 using the local ABI3 bridge. The final simplified suite was not rerun across that full matrix.

[tconley1428]

oOoo