begin
open override fun beginTravelTo(destination: LocationIfc, purpose: MovePurpose, waiter: ProcessModel.Entity): HoldQueue?(source)
Sends the resource to destination and hands back the queue to wait in.
A second call while a journey is under way is a redirection: the target changes and the running journey re-plans at its next step. Over a spatial model that cannot interpolate there is no next step until arrival, so a redirection there takes effect when the leg ends — which is the honest consequence of a geometry with nothing between two places.
Return
the queue to suspend waiter in, or null when the resource was already there