nx_js_run_demo.nx

nx_js_run_demo.nx -- END-TO-END COMPOSITION proof for the sovereign JS engine (WB-JS-001 rungs LEX..CALLBACK). The 60 gate KATs test features in isolation; this runs ONE real, non-trivial program that exercises closures + objects + arrays + map/filter/reduce + a for-loop + member access + .join + Math.max + console.log TOGETHER, through js_run_source, printing real output. No gcc/V8/node -- sovereign.