Constant POLY_BUILTINS 

const POLY_BUILTINS: &[&str];

Builtins whose return type matches their arg type (HLSL “polymorphic” element-typed functions). Used by SymbolTable::infer_expr_type — the same set as BROADCAST_BUILTINS plus a few more pure-passthrough math functions we don’t need to broadcast-rewrite but whose return type is “same as arg”.