The only thing ~/.cache/parvagues/gig-up.log has ever contained is gig-up's own
usage text. --help prints the options and exits 0, the window script saw a zero
and closed itself, and the result was indistinguishable from a successful boot:
a terminal that flashes and vanishes. Nothing had been started, which is how it
was noticed at all -- the LCXL stayed dark, because no launch ever reached the
paint step.

The exit code cannot carry this; --help exiting 0 is correct. So the fence is
whether the launcher reached its own last line: every real path prints
'gig-up done', while usage, an unknown option and any early exit do not. On a
zero with no marker the window now holds, names the symptom (no SuperDirt, no
Ardour, no colours on the LCXL) and exits 2.

--quiet is exempt by construction: ok() is a no-op there, because that mode
exists so the Bridge captures only WARN/FAIL. The test suite holds both ends of
the coupling, so rewording gig-up's last line fails loudly instead of turning
every real launch into a held window.