This. Very few people are doing this right now (probably because it sucks having 5 copies of your app running in parallel on your laptop), but in the past few months models have gotten really good at testing your running app live. If you have an environment where you can run your full app and models can get it at via playwright and chromium, they can click around, take actions, and actually verify that their code works.

With boxes.dev I've starting pushing agents harder to run the full app and test their work end to end, and send me screenshots as proof. This takes time, sometimes up to 30-40 minutes, but is much more likely to be bug free at the end of the day.