For the first time since July, hedge funds and other large speculators are bullish on Treasuries across the yield curve, U.S. Commodity Futures Trading Commission data show. The shift in 10-year futures was particularly striking, with the group adding an unprecedented 255,942 net-long contracts as of the latest figures, covering the week through April 25. Their bias is so skewed toward gains that the group is the most vulnerable to a bond-market selloff since 2008. Their change of heart came at a risky time. While almost no one expects the Federal Reserve to raise interest rates Wednesday, traders are betting that...