scripts/ci/check_os_marker_fakes.py flags test files that make the
interpreter believe it is on macOS (is_macos -> True, sys.platform ->
"darwin", platform.system -> "Darwin") while carrying no `macos_only`
marker: the macOS lane imports only marked files, so such a file is green
on Linux over a faked branch and never runs on the host it exists for.
A `# os-marker: ok — <why>` comment opts a host-independent line out.
_BASELINE holds the files that already faked macOS when the check landed;
a stale entry fails the check so the list can only burn down. Wired into
lint.yml next to the compat-pointer check; two invariant tests cover a
flagged fake vs marked/opted-out files and host-honest platform reads.
bf1c28b480