When Hu Jintao, China’s top leader, picked up the telephone last August to talk to a senior anticorruption official visiting Chongqing, special devices detected that he was being wiretapped — by local officials in that southwestern metropolis. The discovery of that and other wiretapping led to an official investigation that helped topple Chongqing’s charismatic leader, Bo Xilai, in a political cataclysm that has yet to reach a conclusion.