fakeRoomPair

suspend fun fakeRoomPair(hostId: PeerId = PeerId("host"), joinerId: PeerId = PeerId("joiner")): Pair<FakeRoom, FakeRoom>

Build a wired pair of FakeRooms whose FakeRoom.broadcast calls cross-deliver into the other room's Room.incoming, matching the behaviour of a real two-peer room.

val (host, joiner) = fakeRoomPair(PeerId("host"), PeerId("joiner"))
host.broadcast(byteArrayOf(1, 2, 3))
val frame = joiner.incoming.first() // RoomFrame(sender=PeerId("host"), payload=[1,2,3])