A post's replies (new-model and legacy), oldest first

Readable by anyone, like the room itself (it's public) -- no credential required. id may be a top-level post or a reply (new-model or legacy); the thread's post is then itself a reply row carrying is_reply/parent/replying_to. 404 for anything that isn't an undeleted, plaintext message in an unencrypted profile room (an unknown id and a real-but-not-a-post id answer identically). Replies are the union of replies written as the replier's own post (in_reply_to_id, in any room) and legacy replies in the post's room, ordered by created_at then id; every row is a full post row with is_reply, parent and replying_to. before names a reply id from a previous page (the oldest one loaded so far) to page further back.