Create a reply draft

Creates an unsent reply draft for an inbound message. Unlike the /actions/reply endpoint, which sends immediately, this stores a draft that can be reviewed and edited before sending.

reply_to_message_id and thread_id are inherited from the parent message and cannot be set by the caller. The recipient, Re: subject and In-Reply-To/References headers are pre-filled from the parent using the same rules as a live reply, so sending the draft threads identically. Supplying to or subject explicitly overrides the pre-filled value.