He may have descended Air Force One late Wednesday to the cheers of schoolchildren brandishing the Stars and Stripes, and flanked by tech’s most influential tycoons, but it didn’t take long for U.S. President Donald Trump to be put in his place in Beijing. In the first closed-door discussions with his illustrious guest, Chinese President Xi Jinping issued a stinging rebuke regarding American arms sales to Taiwan, warning the superpowers could “collide or even enter into conflict” regarding the self-ruling island, over which China claims sovereignty . Taiwan, Xi said, “is the most important issue in China-U.S. relations.” Given that Trump explodes at even the most trifling perceived affront— pulling 5,000 American troops out of Germany after Chancellor Friedrich Merz said the U.S. had been “humiliated” in Iran—it was telling that Xi felt empowered to lay down the law from the get-go.…