on
Called once per frame sent by a remote participant with Room.send.
This device does not hear its own sends echoed back, unlike Room.PubSub. Delivery is best-effort: a frame the sender marked unreliable may never arrive, and nothing reports the loss. Frames carry no topic and are not replayed to later joiners, so anything that must survive a late join belongs on a PubSub topic instead.
A frame is either text or bytes — read DataMessage.isBinary before taking DataMessage.text or DataMessage.data.