I've built #Enigmatick to manage threading using conversation IDs like Mastodon uses. But that's not aligned with #ActivityPub - or at least it wasn't the least time I looked. ActivityPub uses inReplyTo to indicate direct parent relationships and doesn't have a concept for linking multiple objects under a single ID.

Other systems don't use the conversation convention and that's caused some discord in my timeline. So now I'm learning about closure tables and concepts I probably would already know if I had studied computer science in college. But it's never too late to learn!