UPI Architecture: The Story of How NPCI Became India's L7 Super Switch

It's 12:08 AM in Pune. A student walks up to a momo cart, scans a QR code, taps Pay, and walks away with his food. He doesn't know it. The shopkeeper doesn't know it. Honestly, most developers don't know it either. But in those two seconds between tap and paid, NPCI's UPI switch just performed twent