They use nodejs and React. Yes, for real.
https://xcancel.com/trq212/status/2014051501786931427
> We’ve rewritten Claude Code’s terminal rendering system to reduce flickering by roughly 85%.
tells you all you need to know
and I keep running it remotely through tmux, that explains so many things
edit: if they are writing it in react anyway (sic!) maybe we could at least get a web interface, skipping mapping it to terminal output part ..