By the time Charlotte Wood walked home—if you could call it home—it was light out and already hot. Six a.m.: Much of Shanghai’s foreign population was fast asleep. But the Chinese are early risers, and on the streets around her, the city had begun to wake. Vendors hawked breakfast snacks from wheeled carts: strips of golden-brown fried dough, sticky rice balls filled with pork floss, steaming soy milk sealed in flimsy plastic cups. Merchants unveiled their wares in small shops crammed with towering piles of fruit, on humble blankets laden with onions and . . .