It doesn’t need to be that complex, but it can be that complex without being slow. Claude Code’s interface is extremely simple. It has tons and tons of headroom to tack on performance overhead without it being noticeable at all. You just have to not do dumb things like redraw the entire UI every time a spinner spins.

"We made our app chew up so many unnecessary resources that we can use even more resources in the future, and no one will notice" is not the strongest engineering idea I've ever heard.

It may not be slow, but this crazy complexity is probably a hint at why it can't even scroll up without jumping to the beginning of time.