HDFC Bank Asked This RAG Question — 99% of Engineers Get It Wrong

HDFC Bank asked this exact RAG system design question in a real interview: "Your RAG system answers correctly today. Tomorrow the source document changes. Thousands of cached answers become wrong. How do you invalidate and refresh AI-generated knowledge — safely?" In this video I break down the complete 4-pillar framework top RAG engineers use to answer this — Detect, Invalidate, Refresh, Verify — with the exact interview-ready lines you can say out loud.