v = 10
error: unhandled error reached main: error.Empty
error return trace (most recent call last):
  inner at 244-failable-main.sx:18:17
        if n == 0 { raise error.Empty; }       // pushes a frame
                    ^
  main at 244-failable-main.sx:26:10
        w := try inner(0);                       // raises Empty → propagates to main
             ^