Yuki Jiang works as a consultant at a multinational in Shanghai. But during the city’s harsh lockdown, she took on a second, more crucial job: running a chat group to bulk-order frozen dumplings, chicken wings, and fried rice for her neighbors. Since April 1, when the government locked down the entire city to control a rising Omicron wave, it has struggled to provide essentials to its 26 million confined residents. Supplies have been unevenly distributed, and delivery apps overwhelmed. Desperate calls for food and medicine have filled social media. And where traditional supply lines have failed, a citywide group-buying network…