For a visit dependency A→B, add a hard constraint guaranteeing that A is never assigned while B is unassigned — so the pair is either planned together or not at all.

Current gap

The existing prerequisite-assigned constraint ensures B is never scheduled without A, but nothing enforces the other direction. The solver can schedule A and leave B unassigned — including onto a vehicle that, under coordination: SAME_VEHICLE, can never serve B (outside its coverage area or missing a required skill), making B permanently unassignable with no hard score impact.

Use case

Our preceding visits are parts collections from depots feeding a repair job on the same vehicle. A parts pickup without its repair job is pure wasted work: an engineer drives to collect parts for a visit that isn't happening — and if the pickup lands on a van that can't reach or do the job, the pair can never be completed together. This gap has forced us to move the affected jobs back to manual planning.