replyThread property
ReplyThread narrows that address to one THREAD inside the channel: on Slack it is the parent message's ts, the same value a reply carries as thread_ts. Empty puts the run's status line at the top level of the channel instead. The channel is what decides whether a run narrates at all, so this on its own addresses nothing — a thread with no ReplyChannel is a run nobody hears.
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? replyThread;