You guide the AI with some prompts and give it some guidance on how to scenario-test it. It makes some classes, test methods. Maybe ~2000 lines and you do a quick verification, check if the overall idea looks okay. Ask it to fix a few design things and then merge it.
Its much easier than doing it yourself with all the boilerplate and understanding each esoteric language specific thing. Which library do I use for UDP communication in golang? The agent might have made a good assumption. These kind of things is where it speeds it up.