Client: Entity Back Reference on NetworkedEntityId

[MeFisto94]

Basically, the created entity should have a component (and the related PS), so for instance when entering a car that has already been spawned by another player, we can tell the server that we wanted to enter exactly that car (by looking up if the entity we mount has a network id), otherwise we need to ad-hoc spawn a car and enter that.

yeah imo component is the cleanest solution
technically you can register persistent state without having an actual component
look at what I do in DynamicEntitySystem, you'll just need composite PersistentID with entity id and unique component name