`deploy.allSwarmServices` derives nine service enables and appeared
nowhere in the check, so the tier a service sits on was prose only. The
tenth, the swarm controller, already had this exact pair of cases — it
rides `singleHostSwarm` instead, and swarm-ui follows the controller.
Four cases: the switch turns its nine on, a hive that does not host them
runs none, an operator placing one elsewhere still wins over the
`mkDefault`, and hosting the shared services does not make a hive the
swarm's control plane.
The roster is counted before it is read: `lib.all` over an empty set
holds vacuously, so a roster that lost a member would otherwise turn the
case green by measuring nothing.
Closes#4186
dd9e0bf0b0