Beijing  —  Weeks into the job, Japan ’s new leader has come face-to-face with what it means to cross China ’s red line on Taiwan. In the days since Sanae Takaichi suggested her country could respond militarily if China were to move to take control of Taiwan by force, Beijing has pulled out its economic pressure playbook: warning its citizens against travel and study there, suggesting there’ll be no market in China for Japan’s seafood exports, and unleashing a wave of wall-to-wall nationalist