replyChannel property
ReplyChannel / ReplyThread are WHERE THE RUN NARRATES ITSELF, when the surface that started it has somewhere for it to talk. Empty means nobody is listening and the run simply does not narrate — which is the app surface's case, because /v1/agents/coding hands back a session id and the session stream is a better progress feed than any message could be. It is an ADDRESS and not a token: the engine says "put this text there", and the process that owns the workspace's bot credential is the one that actually posts. So a run reports into a Slack thread without the engine ever holding the token that could post anywhere else in that workspace.
Please note: This property should have been non-nullable! Since the specification file does not include a default value (using the "default:" property), however, the generated source code must fall back to having a nullable type. Consider adding a "default:" property in the specification file to hide this note.
Implementation
String? replyChannel;