Peers join a room and the relay just broadcasts membership (id + dialable
address); peers then connect to each other directly, PAKE-handshake per
link using the room codephrase, and exchange 1MB chunks. Resume reuses
croc's zero-block scan to detect already-received chunks, whole-file hash
verifies completion, and every peer keeps reseeding what it has to others
until stopped (--one-time restores exit-on-complete for a quick fetch).
