A teammate makes the support bot "friendlier." Code review passes. Unit tests stay green — they mock the model. In production the bot stops calling get_return_policy and cheerfully promises a 60-day refund when the real window is 30. Fluent. Polite. Wrong. And every "does this read well?" score still looks fine. I keep seeing the same five traps in agent "eval" dashboards. The full working project (Microsoft.Extensions.AI.Evaluation 10.10, golden set, custom evaluators, fail-closed gate,...