test/xmod/label_test.ww replaces 706_fnlabel_mangle.c and
750_mklabel_modscoped.c with every assertion preserved (fnlabelmangle
fixture run-112 both stages; three mklabel rows with run exits and
module-qualified label needles). Strengthened: fnlabel adds the
cs==ww sepwork .s byte-id the carrier never asserted.