[adenzhou1350]

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Changes

No linked issue.

A thread can cancel the Future after _call_func() checks cancelled() but before set_result() or set_exception(). The resulting InvalidStateError escapes the portal task and cancels its task group. Use set_running_or_notify_cancel() only when the callable has completed, so cancellation remains available while it runs and completion commits atomically.

The regression now follows the review suggestion: a real stdlib Future subclass calls cancel() immediately before set_result()/set_exception(), without an additional cancellation thread or sync/async parametrization. All 8 result/exception cases across the configured backends fail with InvalidStateError when the original from_thread.py is restored. With the fix, tests/test_from_thread.py passes on native Windows CPython 3.12: 222 passed, 4 skipped, 1 existing xfail. Ruff 0.16.10 check/format and git diff --check pass. Full pre-commit was attempted but blocked by Windows application control while starting a hook environment; the full suite, Linux and other Python versions were not rerun for this test-only follow-up. Earlier threaded-test results are historical. Implementation and tests are AI-assisted.

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Fixed big bad boo-boo in task groups

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[adenzhou1350]

@agronholm Could you take a look at this portal Future completion/cancellation fix when convenient? All 20 hosted checks pass. The regression forces the completion race with real stdlib Futures and a second thread; the recorded before/after results cover synchronous/asynchronous callables and results/exceptions. The current blocker is maintainer review; GitHub reports that the branch can be cleanly merged.

[agronholm]

LGTM.