[xOscarCodes]

Linked issue

Closes #1163

What & why

On Windows, isatty() is True for every character device, including the NUL device. A parent gives a child NUL as stdin through subprocess.DEVNULL or Node's stdio: "ignore". In that case the Windows non-TTY fallback in _select_executor_kind() (#46, #136) did not apply, and parsing used a ProcessPoolExecutor. When the parent then ended the run, for example a pre-commit hook with a timeout, Windows did not end the pool workers. Each run could leave up to 8 orphaned spawn_main processes. On one development machine about 1,400 of them collected and held about 7.6 GB.

This PR adds _stdin_is_interactive(). On Windows it returns True only when the stdin handle accepts GetConsoleMode. A console accepts that call, and NUL, files and pipes refuse it. On other platforms the result is the same as isatty(), so the Linux and macOS executor choice does not change. CRG_PARSE_EXECUTOR still overrides everything.

How it was tested

On Windows 11, CPython 3.12 (uv):

uv run pytest tests/test_incremental.py -k ParseExecutorSelection -q
# 6 passed. Without the change in incremental.py, the 3 new tests fail.
uv run --with pytest-xdist pytest tests/test_incremental.py tests/test_main.py -n 4 -q
# 211 passed
uvx ruff check code_review_graph/ tests/test_incremental.py
# All checks passed
uvx mypy code_review_graph/incremental.py --ignore-missing-imports --no-strict-optional --follow-imports=silent
uvx mypy code_review_graph/incremental.py --ignore-missing-imports --no-strict-optional --follow-imports=silent --platform linux
# no issues in both
uvx mypy code_review_graph/ --ignore-missing-imports --no-strict-optional
# 9 errors in 3 other files on Windows, the same 9 without this change (for example SIGKILL in multi_worktree.py)

New tests:

• test_windows_nul_stdin_uses_threads: Windows, isatty() True, no console handle, so the result is thread.
• test_windows_console_stdin_keeps_process_default: Windows, a console handle, so the result is process.
• test_real_nul_stdin_is_not_interactive_on_windows (Windows only): a real child with stdin=DEVNULL reports isatty() True, _stdin_is_interactive() False and executor thread.

Measured effect on a repository with about 650 files: a full build with the old selection reached 8 pool workers in 58 s. With the thread executor it reached 0 workers in 60 s.

Limits:

• The full suite did not finish locally. Two Windows runs stopped at about 74%, one at a time limit and one when the session restarted, so I rely on CI for the rest of the suite. Those partial Windows runs showed some failures in tests that this change does not touch. I did not compare them against staging.
• A real interactive console was not tested end to end. That case is covered by the unit test with a stand-in for the console check.

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