Wall Street’s rally sputtered as concerns about credit quality hit a pair of regional banks, underscoring the fragility of a $28 trillion bull market showing signs of exhaustion. Bonds and gold rose.Following an earlier advance driven by another solid outlook for artificial-intelligence demand, the S&P 500 fell about 1 per cent as two regional lenders disclosed problems with loans involving allegations of fraud, adding to concern that more cracks are emerging in borrowers’ creditworthiness.Shares of Zions B ...