It began as a feel-good story for China's modern age that played out in the bright glare of social media. Liu Xuezhou, a teenage teacher in training who had been adopted as an infant, found his birth parents after posting a video about his search. In a remarkably short time, police found them and organized a meeting. On Douyin, the Chinese version of TikTok, Liu shared photos of the reunion dinner, his birth father beaming beside a police officer, as well as a screenshot of his birth mother asking for an address to send winter clothes. But within weeks, the…