importThreadDiscussion
Import an existing external conversation as a discussion on a Plain thread, backfilling all messages. Currently supports Slack threads via permalink — the entire thread (root message and all replies) is imported. If the Slack channel is not yet connected to Plain, the bot will automatically join and register it as a DISCUSSION channel (requires the connectedSlackChannel:edit permission). Private channels must have the Plain bot invited via /invite @Plain first. The call is idempotent: re-importing the same Slack thread onto the same Plain thread resumes from where the previous import left off; importing onto a different thread returns an error. Threads with more than 800 messages cannot be imported.
importThreadDiscussion(input: ImportThreadDiscussionInput!): ImportThreadDiscussionOutput!
