ServiceKind

What a vehicle is doing for itself when it is not carrying anything.

Sealed rather than an enum so that adding a kind is a compile error at every exhaustive when that must handle it. This is where the exhaustiveness argument actually bites: Task itself cannot be sealed, because it must be a QObject and QObject is an inner class, and Kotlin refuses sealed inner. Task's hierarchy is closed by construction -- a transport, an errand and a line cycle, all created by the dispatcher -- whereas the service kinds are the thing later work extends.

Inheritors