Stock forecasters in search of an early-warning system for the next Chinese bear market are zeroing in on the country’s record $358 billion pile of margin debt. When that three-year build-up of leveraged positions starts to unwind, regulators will struggle to limit the selloff, according to Bocom International Holdings Co. and Rabobank International. Almost all of this year’s biggest declines in the Shanghai Composite Index, including a 6.5 percent slump on May 28, were sparked by investor concerns over margin-trading restrictions. The securities regulator announced plans Friday to limit the amount brokerages can ... (full story)