Before any of the systems on this site, there was a small one: BlueLightMeter.com, a single-purpose site built with Tailwind, and the first thing I built with a model doing most of the typing. It is no longer online. I took it down when the next project started, and it earned its place here for one reason.
The model I was using at the time kept breaking one thing to fix another. Ask for a change to the layout and the form would stop submitting. Fix the form and a class would vanish from the header. Every fix was locally correct and globally careless, and the frustration was real enough that I nearly concluded the whole approach was a novelty.
What I concluded instead was that the model was not the problem. The absence of structure around it was. There was no test that said what "working" meant, so nothing told the model, or me, when a fix had cost something elsewhere. There was no review step between a change and the live site. And there was no separation between the thing being built and the thing doing the building, so a mistake in one was immediately a mistake in the other.
Every system I have built since carries the answer to that first site. A run that did not leave its receipt did not happen. A person decides what ships. The agents that run the operation are not the agent that builds it. Those rules did not come from a book; they came from watching a header class disappear for the third time.
My own answers, from my own work. They change when the work does.