A slice/str ELEMENT of an indexed expression passed as a call-arg
pushed one word instead of the 24B/16B header — the predicates had no
N_INDEX arm, so element-typed args fell to the scalar path (review
findings #45/#46). Read the element-type stamp; dual-stage rows in
989_idxarg_run pin cs==ww (red 2/8 on pre-fix binaries).