Braintrust solutions engineer: "The best LLMs don't always guarantee consistent performance" That sentence is why a prompt edit needs tests before the edited prompt answers real user requests A playground run can look better while the same prompt lowers quality on messy inputs The workshop shows the minimum eval loop: task, dataset, score, offline testing, online logs, human review The article below maps the same point to retrieval, hallucination checks, versioning, and prompt-change regression tests Watch the workshop, then read the article before the next prompt edit ships without a regression test