Groupings this class prepared in advance, fitted to who is here now.

Host only. A grouping is saved against the SECTION (organization_groups), so this resolves the room to its section and reconciles each one against the current participants — the teacher sees "3 rooms, 2 people missing, 1 to place" before applying anything, rather than finding out afterwards.

A room with no section has nothing to offer and says so with an empty list, not an error: a personal call is not a broken class.