Table-driven, modelled on 953: each row does (a) cstage build+run+exit
and (b) w6c vs w6c_ww .s cmp. Rows cover FACE X (0f64 compare false +
true case, 8f64 arith) and FACE Z (tuple-field f64 compare) plus the
let-bound control that was already correct. Fails on master e784968
(x_cmp_false 1!=0, x_arith 100!=80 + byte-id divergence, z_tuple_field
5!=9); passes on the fix.