Raid handles
Raid handles returned by LevelRef::raid, raid_at and raids resolve their
own loaded server level even while another dimension is in place. Raid reads,
omen-level writes and stop do not swap levels. Raider lists and living health
come from that level's mobs; raid ids are local to a level. A closed level, an
earlier world epoch or a client refuses the handle. Entity handles in a parked
raid's member list keep their identity; their ordinary entity operations still
require the entity's level to be in place.