nx_js_es_census.nx

nx_js_es_census.nx -- MEASURE the modern-ES surface of the sovereign JS engine (present vs absent), so the SPA-giant arc builds the RIGHT features in priority order (data-driven, no-wave). Each probe runs a real snippet via js_run_source; PRESENT iff it yields the expected value (absence usually = parse error). GREEN iff the census is VALID (pos-control PRESENT + neg-control ABSENT) -- NOT iff all present. The gaps ARE the deliverable: they tell us exactly what real bundles (React/etc.) need that we lack.