More of whatever you had in mind.

Clearly there are few limits to what you can implement with AI agents today.

Depending on the complexity, you will spend a lot of time QA testing, giving feedback, and iterating.

One can take shortcuts such as porting existing software, as you mentioned. Many are just content publishing crappy novel software that they barely tested.

You don't need to do that. No one is forcing you not to QA test and iterate until you have a good product.