The Prompt Engineer Who Quietly Became Your Only Eval Set Reader
The eval set is a file. It is also, secretly, a theory of what the AI feature is for. The two are not the same thing, and the team that confuses them has built a quality gate whose calibration depends on a single human's working memory. When that human leaves, the file stays and the theory walks out the door.
This is the failure mode you don't see in the org chart. You scoped a prompt engineering role. You hired someone good. They shipped the v1 prompts, looked at the thin benchmark, and rewrote it into something rich — a taxonomy of failure modes, weights per category, a labeling rubric that disambiguates edge cases. The eval set became the contract for "is this model good enough to ship." Six quarters later you discover that the contract is unreadable by anyone except the person who wrote it.
