If You dont write code - who you are? Everyone is talking about prompts. About token budgets. About cognitive surface. But I think we're still looking at the wrong unit. The unit is the interface boundary . Always was. Back before any of this existed Back when I was writing SQL scripts and mappers by hand, I already had this principle baked into how I worked: every module should know only its contract. Not where the data came from. Not where it goes. Just: here's input, here's output, here's the guarantee. Think of it like a bakery. The baker doesn't care if the flour came from the warehouse or yesterday's leftover stock. Doesn't care where the bread ends up - the store shelf, a restaurant, a catering order. He just bakes. His job is defined by its boundaries, not by the full supply chain. That's how I tried to design every system. Each module gets a clear spec. It does its one job. It exposes a clean interface. It knows nothing about its neighbors' internals.…