By most measures, markets remain on strong footing. Economic data continues to surprise to the upside. The Federal Reserve has extended a fresh lifeline to Wall Street. Stocks are close to recent highs.But beneath that surface, there are signs of a shift.Risk-loving day traders are stepping back from the market’s frothiest corners — bets that soared through the summer on little more than momentum and hype. In recent days, money has flowed out of exchange-traded funds focused on frontier technologies and hig ...