Even by the rough-and-tumble standards of China’s stock market, it was a chaotic 29 minutes. With share prices going into free fall almost as soon as local exchanges opened, market gurus at Huaxi Securities Co. were at a loss to explain why. One manager of $46 million in Shanghai liquidated all his holdings. Other investors, including a top-performing hedge fund, tried in vain to cash out as circuit breakers brought trading to an abrupt halt. By 9:59 a.m. local time it was all over — except that it wasn’t. Next came a torrent of calls from angry clients upset by the carnage in a week that’s seen two abbreviated trading sessions and a 12 percent tumble in the benchmark CSI 300 Index. And it’s only January 7th.