A stock selloff that at one point rivaled any of the last two years was wiped out as dip buyers emerged by Monday’s close, the latest breathtaking reversal in markets rattled by geopolitical tensions and the Federal Reserve’s campaign against inflation. In a session marked by explosive trading volume and wild market swings, the S&P 500 rebounded after tumbling as much as 4% earlier in the day. Retail, energy and industrial companies led gains in the benchmark gauge.