Sender's signaling session id from the wire envelope, when the provider
surfaces it. Used to scope per-(cid, sid) ordering of content_state
revisions so a rejoin restarting at revision:1 is accepted by identity.
Absent when the provider does not carry a session id.
Sender's signaling session id from the wire envelope, when the provider surfaces it. Used to scope per-
(cid, sid)ordering ofcontent_staterevisions so a rejoin restarting atrevision:1is accepted by identity. Absent when the provider does not carry a session id.