In China , life is now governed by an official coronavirus health app on pretty much everyone's smartphones. More important than a passport, more personal than a photo, the app decides who can go where. It can force people to cancel trips, retreat into isolation, or even seek hospital treatment. Not having it really isn't a viable option for most people in China. Without it, you can't even get to work. Once downloaded, the software operates like a traffic light: Green means "safe from COVID," and allows the holder access to all buildings, including grocery stores and offices. There's no...