Server v0.5.21. Comments feeds are live — the feature previewed in the last entry shipped today, and its first real thread was Manton Reece saying hello.
Here's how it works. Any post that has replies now carries a new element in its feed item:
<source:comments count="1" feedUrl="https://users.rss.network/manton/comments/204.xml"/>
The count says how many direct replies the post has; the feedUrl points at a small RSS feed containing them. That comments feed is a static file on S3, published alongside the user feeds, and its items are ordinary items — description, pubDate, guid, source:markdown, source:inReplyTo pointing back up at the parent. When a reply has replies of its own, its item carries its own source:comments, so an entire conversation is traversable from the feeds alone, one level at a time, every level the same shape.
Because a comments feed mixes authors, each of its items also carries RSS core's <source> element for attribution:
<source url="https://users.rss.network/dave/rss.xml">Dave Winer</source>
— the author's display name and the address of their home feed. The everyone feed, which mixes authors the same way, now carries <source> on its items too.
The feeds rebuild automatically: adding, editing, or deleting a reply republishes the parent post's comments feed, and also the parent author's own feed, since the count on their post just changed. Live example, the first thread: manton's feed → the comments feed for post 204.
Later the same day, two finishing touches. A backfill published comments feeds for all 74 existing conversations, so every feedUrl the feeds advertise now resolves — including the threads that predate the feature. And a subtle case is covered: when you reply to a reply, the middle post's comment count now updates in its parent's comments feed too, so a program walking the tree never hits a level that doesn't know about the one below it. (That one was found by writing a demo app against the feeds — the tree is now walkable all the way down, and we've done it.) source:comments is documented in the source namespace.