Early 2000s tech could absolutely handle LLM agents as a client. They output like 1-2kbps and even dial up modems would have plenty of capacity for other traffic.

The UI itself requires laughably simple tech. The idea that a markdown renderer that can produce HTML at 50MB/s would use much CPU to process incoming hundreds of bytes per second is insane. CPU should be idle even if doing that constantly. Nevermind that between turns it has nothing to do whatsoever and should use zero CPU at all.