I think I have it working now.
I spent way too long reading about the comment API (which i am now convinced is a figment of my imagination) and wfw:comment and wfw:commentRss and all that jazz. Theoretically is is working now. Or, as Paul put it, it is “as non-working as everyone else’s”
I think Feedburner hates me. But in theory there is now an “add a comment” link in my feed (which I think technically was *supposed* to be a comment count) and in theory it points to the right page. Last time I tried it went to the permalink instead of the comment page. I might or might not have actually fixed that.
My brain hurts.