The WALK string the facet gate injects into the page moves to a browser-free
module, internal/lib/facet-walk.mjs; the gate imports it, and
internal/check-facet-shape.mjs imports the same string and evaluates it on both
engines' source shapes without a browser. check:facet-shape ran from the browser
gate's own file, so the runner routed it to the browser slot; now it is headless
and joins gates:pre. Poisoned (the { geojson } unwrap disabled) it reports 4/5.