How would you design an optimistic update system for a social feed — handling rollback, conflict resolution, and partial failures without jarring UX?

Imagine you're building with LEGOs and you put a block on top before checking if it fits. If it doesn't, you quickly take it off without knocking everything down. That's what optimistic UI does—it shows the change right away, then fixes it if something goes wrong, so the game keeps feeling smooth.