The error CHANGED on the VM: 'no polkit agent' -> 'access denied by
policy' — the agent unit works; polkit now denies because the user is
not in the libvirt group (fresh run without picking QEMU from the menu,
or no re-login after the pick).
install_session_prereqs now adds the user to the libvirt group whenever
libvirt is installed (idempotent via id -nG check), decoupled from the
advanced-menu choice. Applies after re-login.
Pathfinder
e99c60a073