Three Gates Before an Interface Changes
Who approves a change to a module interface?
Three gates, in order. A product manager identifies market demand that affects revenue, retention, or compliance. A system architect decides whether that demand belongs in the provider's domain, the consumer's domain, or neither, and whether an operation can satisfy it without changing the structure. The CTO approves the change only when it is worth the coordination cost it imposes on both teams. A request that starts in an engineering team is rejected by default.
When is an interface change legitimate?
Twice in a company's life. At the decoupling point, after product-market fit, fluid interfaces have to freeze. And when one module has grown until its purpose must split into two domains, two teams, and two interfaces. Adding a field because one team wants it, renaming a field so the API looks cleaner, or splitting a response for convenience is internal politics. Both legitimate moments still pass through the three gates.
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