Four ways a baseline quietly destroys the anomaly detector built on it

Every anomaly detector answers one question: compared to what? That comparison, the baseline, is where I lost the most time on this project, and every failure had the same signature. Nothing errored. No test went red. The numbers stayed plausible. The detector just quietly stopped detecting. Four of them, in the order I found them. 1. The peer group contained the client it was judging Cold-start clients have no history, so they're compared against a pool of other clients' recent benign windows.…