Custom lexicon for issues, issue state (open, closed) and issue comments. The case with issue_at is a bit weird since we have a circular dependency: the issue record requires the issue_id, and the issue entry in the db requires the issue_at. To resolve this we write to the db without the issue_at, fetch the issue_id, create the issue record on the PDS, and then update the issue_at (with SetIssueAt). It's not great, but whatever.