Round 2 changed the incus-admin path from a skipped group step to a real
`usermod -aG incus`, but `bin/box` help still described the superseded
design — telling operators the group step is a no-op that will not happen
(it does) and that a bare revoke has no membership to drop (it drops one).
The help is the pre-run contract: it is what an operator reads to decide
whether to run the command at all, so prose that denies a mutation the
command performs is the same class of defect the rest of this PR exists to
remove. Both sections now describe the current behavior, and `help revoke`
carries the consequence the operator would otherwise discover: once `incus`
is gone, a later `gpasswd -d <user> incus-admin` lands them in NEITHER
group, so grant's "no re-grant needed" holds only while they hold `incus`.
Pinned in both directions — the current sentence must be present and the
superseded one absent — so the prose cannot drift from the scripts again.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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