The best engineering in Apple's $1,999 foldable is a half second of software. Foldables have always had a tell. Open one and the OS treats it as a display switch. It kills the layout on the small screen and redraws it on the big one. Your brain catches the flicker, and the device reads as two phones sharing a hinge. Apple attacked that with a hardware constraint. Both displays on the iPhone Duo share the exact same aspect ratio. That's why the closed phone is shaped like a passport, wider…