The first time I heard the term “carry trade” was in June 2007. I was standing by an elevator bank as bond trader Dan Fuss explained to a cluster of anxious money managers the essence of Bear Stearns’ bailout of a pair of its hedge funds announced earlier that day. It had been a carry trade, Fuss told them, harder to understand than a classic currency carry because it involved mortgage market derivatives, but otherwise no different in its fundamental structure: borrow at low rates in one market in order to invest in high-yielding assets in another, and hope that…