From windowless processes (the pythonw gateway and the kanban workers it
spawns), three spawn paths flash visible console windows on Windows:
1. tools/env_probe.py::_run() ran its interpreter/pip probes
(python3 / python / pip / 'python3 -m pip' / PEP-668 check, ~5 per
worker start) without creationflags — one console flash per probe.
2. tools/lazy_deps.py had four spawn sites with the same defect:
'uv pip install', the 'pip --version' probe, ensurepip, and the
pip install fallback.
Both now pass creationflags=windows_hide_flags() (CREATE_NO_WINDOW on
Windows, 0 on POSIX) — stdio capture still works because the child is
hidden, not detached.
3. CPython 3.11's platform.win32_ver() unconditionally calls
_syscmd_ver(), which runs 'cmd /c ver' via
subprocess.check_output(shell=True) with no window suppression. Any
dependency touching platform.uname()/version()/platform() at import
time flashes one 'cmd' window per windowless process. New helper
_subprocess_compat.suppress_platform_ver_console() (Windows-only,
never raises) stubs platform._syscmd_ver so win32_ver() falls back to
sys.getwindowsversion().platform_version — verified byte-identical
platform.platform() output on CPython 3.11
('Windows-10-10.0.26100-SP0' either way). Called at the top of
hermes_cli/main.py, right after the hermes_bootstrap guard, before
heavyweight imports.
Verified on Windows 11 by polling EnumWindows at ~15 ms and attributing
new visible HWNDs to the suspect process tree (conhost child presence is
NOT evidence of a visible window — it appears even with
CREATE_NO_WINDOW). Tests: tests/tools/test_windows_native_support.py,
test_env_probe.py, test_lazy_deps.py, test_lazy_deps_durable_target.py —
153 passed; the 3 failures are pre-existing on upstream/main in a
Windows environment (POSIX-only assertions and NTFS chmod semantics).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Cal Marley
5c5960d9f9