In this case, it makes sense to me to thread replies as you’ve done, though obviously the icons weren’t apparent to me.
One thing I’m confused about is why my reply is categorized as a bookmark, since it is marked up with ‘u-in-reply-to’ and not ‘u-bookmark-of’. Either way, I’ll continue to post to /en/bookclub and will let you know if I have any other comments.
Appreciate the help!