LLM agent harnesses make it possible to do: CLI, TUI, REST API, web front end + Electron, native (I do macOS first, which then makes iOS/iPadOS almost trivial, followed by Android), and if I’m feeling ambitious, Windows (native) and Linux (usually Qt).

It’s much easier for the clanker to loop on testing / improving the TUI than a real GUI. It also means it can work on the app without an API/REST/HTTP/Java/Script ball of mud in the middle.