Windows CI (run 415) ran the discovery tests: 48 passed and one failed,
because port listing reads Linux sysfs and the test assumed it exists.
That is a real limitation, not just a bad test - and in the example it
meant `all` would listen and sweep and then abort on the serial step,
throwing the results away.
The serial step in `all` is now a printed note on failure; the standalone
`serial` command still errors. The Linux-only test is gated to Linux and
a counterpart asserts that off Linux the listing is an error, not a clean
empty result.
octoturge
9061d39684