A s the Taliban entered Kabul, Afghanistan , on Aug. 15, 2021, Qudrat Wasefi, a resolute 22-year-old trumpeter, flung open the windows of his music school’s empty wood-paneled studio and started to play as loudly as he could.  “I thought it was my last time,” he tells me, crammed into a booth at a taqueria in Cambridge, Massachusetts, while Harvard Square’s lunch rush is at full tilt. Beside him sit Bob Jordon and Derek Beckvold, two Americans who once taught him scales in Kabul and understood