Architecture that lives only in people's heads doesn't survive agents.
For most of my career, the real rules of a codebase weren't written down.
People knew them.
Senior engineers knew which layers could talk to which. They knew which dependencies were forbidden, which schemas were effectively frozen, and which shortcuts would create problems six months later. New engineers learned those rules the traditional way: break one, get caught in review, get the explanation, and eventually remember not to do it again.
It wasn't perfect, but it mostly worked.
