After seeing a recent video from Theo, I wanted to see how far I can take a harness contained in just 30 lines of JavaScript. Turns out - far enough to be useful, it handles simple tasks just fine, works with both cloud and local models, uses just three tools (but can do with a single one, frankly speaking), cleanly handles detached commands or cancellation mid-run, has non-interactive mode and can be run with NPX.