'incus list' failed because this shell had no permission to reach the daemon,
incusOk returned null, and the caller wrote ?? "[]". So 'mesh-lab list'
printed 'no scenario instances standing' -- confidently, about a question it
had never managed to ask.
The comment on incusOk warns about exactly this, in those words: absence and
success made indistinguishable. Three of its own callers then did it. Two
listings and the live diagram, which would have drawn an empty scenario rather
than fail -- a picture that is confidently wrong, which is worse than none.
Anything enumerating what exists now goes through enumerate() and throws.
incusOk stays right where failure genuinely means no, like instanceExists,
and there is a test holding that line so this does not get over-corrected
until nothing can be asked at all.
Worth noting 'mesh-lab check' already diagnoses this precise cause, down to
'a session that predates it cannot see it'. The diagnosis existed; the
listing just never asked for it.
