66ba36ec81
CI slice 8/8 red:
test_verify_core_dependencies.py::test_uses_virtual_env_from_environment
AssertionError: assert None == PosixPath('.../newvenv/Scripts/python.exe')
The Phase 2 reviewer flagged this exact risk (W4) and I under-weighted it as
"latent, not broken". It was neither — it was already failing.
The suite exercises Windows-only paths on Linux CI by patching predicates
(`hermes_cli.main._is_windows`, `is_windows`, `platform.system`). Routing
those call sites through a helper that reads `sys.platform` unconditionally
meant the patches no longer reached the path derivation: the test built
`Scripts/python.exe` while the code looked for `bin/python`.
venv_bin_dir/venv_python_path now take an optional `windows=` verdict,
defaulting to the host. Every converted site passes its own predicate, so
the patched-predicate coverage is restored — the dedup keeps the layout in
one place without hijacking the platform decision.
Verified by causation: dropping `windows=` reproduces the CI failure exactly;
restoring it goes green. Added two regression tests, including one asserting
a patched `_is_windows` still reaches the derivation.