Upon first glance, a 13% plunge in a top chip stock might look problematic for the overall market. Especially if the reason for the drop is weakness in the market's hottest area. That's why it was surprising on Thursday — after Broadcom reported underwhelming AI demand and saw its stock tumble double digits — that the S&P 500 and Dow still closed at records. The tech-heavy Nasdaq Composite was basically flat. The Dow? Up nearly 900 points. But surely the Philadelphia Semiconductor index, chock