How do you ship a software product with 0 lines of manually-written code?

A friend asked me this today, and I realized I didn't have a simple answer. So I dug deeper.

It turns out the answer is in how you engineer your harness.

Wait now, what? What is harness engineering?

There is a reason this is the most important trend right now around coding agents. The biggest question these days is how to validate AI-generated code without reading every single line. How do you make sure an agent doesn't break production or delete your data?