[The content of this article has been produced by our advertising partner.] In cities around the world, the mechanics of local government often grind slowly: a pothole reported but not repaired, a noise complaint logged but unanswered, a maze of departments passing responsibility from one counter to another. Yet across China, a simple five-digit number—12345—is reshaping how governments respond to citizens and, increasingly, how they anticipate problems before they arise. What began decades ago...