Honor kill_after_timeout with output streams

[pick7]

Summary

• Start the existing timeout watchdog when output_stream is used.
• Keep the watchdog active until the subprocess has actually exited.
• Add a regression test where stdout closes before the child process sleeps.

Fixes #1762.

Validation

• .venv/bin/python -m pytest -o addopts= test/test_git.py
• .venv/bin/python -m ruff check git/cmd.py test/test_git.py
• .venv/bin/python -m ruff format --check git/cmd.py test/test_git.py
• .venv/bin/python -m mypy git/cmd.py

AI agent disclosure

This pull request was prepared and submitted by OpenAI Codex acting as an AI agent through the contributor account.

[Copilot]

Pull request overview

This PR fixes Git.execute(..., kill_after_timeout=...) so timeouts are enforced even when output_stream is provided, aligning behavior with the documented intent and closing the gap described in #1762.

Changes:

• Start and manage the existing timeout watchdog during the output_stream execution path, keeping it active until the subprocess exits.
• Refactor timeout error construction into a helper used by both communicate() and output_stream paths.
• Add a regression test where the child closes stdout early and then sleeps, ensuring kill_after_timeout still triggers.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
git/cmd.py	Starts/cancels the timeout watchdog for output_stream runs and centralizes timeout error creation.
test/test_git.py	Adds a non-Windows regression test to confirm kill_after_timeout is honored with output_stream.

Comments suppressed due to low confidence (1)

git/cmd.py:1490

• communicate() starts the watchdog timer but only cancels it on the success path. If proc.communicate() raises (e.g., due to an I/O error), the timer remains scheduled and can later kill the process (or a reused PID) after execute() has already failed. Cancel the watchdog in a finally to ensure it is always cleaned up.

            def communicate() -> Tuple[AnyStr, AnyStr]:
                assert watchdog is not None
                assert kill_check is not None
                watchdog.start()
                out, err = proc.communicate()
                watchdog.cancel()
                if kill_check.is_set():
                    err = make_timeout_error()
                return out, err

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[Byron]

Thanks a lot, this circumstantially looks good to me.