There was a sequence that could bring down a feed rebuild: someone replies to a post, the author deletes the post, then the reply gets edited. Rebuilding the comments feed found the parent gone — deleted posts are filtered out of every query — and crashed trying to read it. Now the build answers the way this server always answers: "Can't build the comments feed for post N because the post has been deleted."
Also: this file moved from server/docs to server/code. Worknotes live with the code, because you need the worknotes to read the code.