The 8e gate compared uname -s to the bare literal MINGW64_NT, which
never matches the real value (MINGW64_NT-10.0-...), so the POSIX
branch silently ran on Windows and looked for the extensionless shim
that #929 no longer installs. Branch by platform prefix: Windows
expects the .cmd shim and the absence of the legacy extensionless
twin; POSIX unchanged. Content checks (never blocks, delegates to
hook-augment) now run on both.
Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>