isHeldByStationaryVehicle

True when a vehicle is standing in this zone that nothing in the model will move again.

The one case where "this space will never come free" is a judgement the guide path can actually make. The vehicle carries nobody, has no route under way and waits for nothing (GuidedTransporter.isPermanentlyStationary), so no event on the calendar and no process in flight is going to shift it. A closure asked for over such a zone is granted only if some other part of the model dispatches that vehicle.

Deliberately narrow, and the narrowness was bought. An earlier version of this also called an untimed hold indefinite, on the reasoning that a timed hold puts its release on the calendar and an untimed one does not. That is wrong, and one example proved it: a spill entity holding space through trySeizeZones releases it when its process resumes, which is every bit as certain as a clock and simply invisible from here. The overreach produced 139 warnings in a model with no faults in it at all. A holder's untimed hold and a holder that has forgotten to release look identical from inside the guide path, so this does not guess between them.

A reading about one instant rather than a proof, for the same reason the deadlock detector's idle obstruction is: an entity may seize the vehicle a moment later. That is why nothing is raised or warned on the strength of it -- a model asks this and decides for itself.

False for a free zone whatever is reserved or present in it. A reservation is a different question with a different answer -- see firstPromisedZone.