`users apply` converged group `incus` with a bare `gpasswd -d`, the same
move it makes for `rig-admin` and `rig`. Those two are rig's. `incus` is
box's, and `box revoke` does strictly more with it: it says out loud that
supplementary groups are read AT LOGIN, so a session the dropped operator
already holds keeps the Incus socket until that session dies, and it hands
over `loginctl terminate-user <user>` as the remedy.
rig logged "removed <user> from incus" and moved on. An operator who
dropped someone from the users file and watched apply succeed believed the
VM access was gone — and was wrong for as long as that user held a session.
Both removal paths — the per-user convergence loop and the dropped-user
sweep — now route the incus group through one `drop_incus` helper that
calls `box revoke`, keeping a single owner for the group. Never `--purge`:
that deletes the user's boxes, images and project, and destroying someone's
running machines is not a convergence step; it stays an explicit admin act.
The exit code is not trusted (the #12 lesson bootstrap already applies to
box's installer): a revoke that returns 0 with the membership still
standing has not closed the socket, so the effective state is checked and
rig falls back to removing the group itself — as it also does on a host
where box is not installed. Every fallback path carries the session warning
in rig's own voice, because the silence was the bug. The absent-group case
needs no new guard: `id -nG` cannot report a group that does not exist, so
the existing `in_group` test at both call sites is already false on a
host=no box or one where `box setup-host` never ran.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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