Say who answers for a location when its primary head does not. An empty list clears every
Locations
Say who answers for a location when its primary head does not. An empty list clears every
alternate — it does not touch the primary head, which is a plain column written through api.update_record like any other.
Replaces the whole list in one call, the same shape as api.set_category_sites: the caller sends what should be true now, not a delta.

