RoomRegistry.prototype.peek(name: string): Room | undefined
Returns the named room if one already exists, without creating it.
The non-allocating counterpart to RoomRegistry.get. It is a
bare map read by design: it must not touch RoomRegistry.#neverJoined
in either direction, because adding to that set would mark a room already
in use as abandoned, and reclaiming from it on a read path would make a
lookup that promises to change nothing dispose rooms.
Room | undefined
The room, or undefined when no room of that name exists