Conversation (or flow) name.
Conversation key (chat id, or chatId:senderId per group participant).
'unforwardable': it kept no checkpoint; 'changed': a forwarded flow changed on this replica.
OptionalstartedWhen it started on the previous replica (epoch ms), when known.
OptionalstartIts initial c.state, when that was plain JSON.
OptionaltraceTracing (BotConfig.telemetry): W3C trace context of its last turn on the previous
replica, to link a migrated conversation's spans to it ('restart' does it itself).
A conversation the replica that took the chat could not continue (see HandoverFallback).