test(chrome): compare both selector matchers over one live page

Selector matching is written once per runtime: internal/hierarchy over the
dump, web-runtime.ts over the DOM. Nothing made the two agree, and a
selector that resolves on one and not the other is silent, since an empty
match yields no action and the run still passes.

pkg/spec/src/web-runtime.ts

@@ -589,6 +589,7 @@ installRuntime(
 // so these are stripped from production output; they only exist for unit tests.
 export const __testing__ = {
   host,
+  buildAx,
   seedBigInt,
   collectTargets,
   targetElements,