resumeToken

The joiner's reconnect credential, available after the admit handshake completes.

Non-null on a SessionRole.Joiner room once the host has sent its RoomId via the Welcome frame. Null on a SessionRole.Host room (the host does not reconnect to itself) and null on a joiner room whose handshake has not yet completed.

Callers that need to reconnect after a transport drop should save this token. Present it to resume to attempt re-entry within the reconnect window.