OptionalparticipantsMember callsigns from the comma-separated <chatroom-participants> list.
OptionalroomTAKTALK room ID from <chatroom-id>.
OptionalroomHuman-readable room name from <chatroom-name>.
OptionalsenderDEPRECATED in v0.3.2 — always equals envelope TAKPacketV2.callsign in valid packets, so the duplicate wire byte was redundant. Builders stop writing this field; parsers still read it for one release so v0.3.1- encoded packets decode cleanly. To be removed entirely in v0.4.x.
TAKTALK room/membership broadcast (CoT type y-).