If China invades Taiwan and cuts off its chip exports to American companies, the tech industry and the U.S. economy would be crippled.Federal officials have for years tried to wean Silicon Valley from its dependence on Taiwan, an island democracy roughly the size of Maryland that makes 90 percent of the world’s high-end computer chips. In secret briefings held in Washington and Silicon Valley, national security officials warned executives from companies like Apple, Advanced Micro Devices and Qualcomm that China was making plans to retake Taiwan, which Beijing has long considered a breakaway territory. A Chinese blockade of Taiwan, the...