ID Column

When Your Data Pipeline Leaks, Cross-Validation Won't Catch It

Your machine learning pipeline can cheat, and your cross-validation metrics will never know. An ID column, a date string, and a missing value taught that uncomfortable lesson. What seems like a robust pipeline often leaks information forward in time, letting your model peek at data it should not see. We saw a related pattern in *When Tools Break, Your AI Agent Keeps Writing Confident Answers*, systems hiding failures behind green dashboards. Trust your validation metrics less. Question everything your pipeline quietly assumes.