Function author_writer 

pub fn author_writer(record_writer: &ActorId, author: &str) -> ActorId

The actor author’s mount edits a record as, when the record’s writer is record_writer and the host asked for per-author writers; mounts of one profile and device share a document, so this keeps each author’s edits apart. Unique per writer, and the same after a reopen, so history names the same author.