test(chrome): compare the facts both hosts derive from one DOM

The existing parity harness hand-authors the facts on both sides, so it proves
that given identical facts both hosts select identical candidates, and says
nothing about the two code paths that derive those facts from a real page. Four
divergences lived in that blind spot and it passed throughout.

This drives one real page and compares clickable, enabled, editable, scrollable
and positiveBounds element by element, plus the element sets themselves, which
is what catches a host that omits html or includes head. Reverting any of the
four fixes makes it fail naming the element and the fact.

Claude-Session: https://claude.ai/code/session_01A5KmftdEJ49A9z5mF5ESrX

pkg/spec/test/dom-facts-probe.ts

@@ -0,0 +1,41 @@
+/// <reference lib="dom" />
+
+// The V8 host's fact producer, read back element by element.
+//
+// internal/driver/chrome/fact_parity_test.go bundles this probe into a live page
+// and compares what it returns against the hierarchy dump the goja host reads
+// off the SAME page. Both sides derive their facts here, in production code:
+// collectTargets is the shipped walk, and targetElements is the shipped
+// enumeration domain, so the id at index i names the element facts[i] describes.
+// The dump carries that id as `resource-id`, which is what the Go side joins on.
+
+import { __testing__ } from "../src/web-runtime.ts";
+
+const { collectTargets, targetElements } = __testing__;
+
+function domFacts(): unknown[] {
+  const elements = targetElements();
+  const facts = collectTargets();
+  if (elements.length !== facts.length) {
+    throw new Error(
+      `collectTargets reported ${facts.length} targets over ${elements.length} elements`,
+    );
+  }
+  return elements.map((element, index) => {
+    const target = facts[index]!;
+    return {
+      id: element.id,
+      tag: element.tagName.toLowerCase(),
+      clickable: target.clickable,
+      enabled: target.enabled,
+      editable: target.editable,
+      scrollable: target.scrollable,
+      width: target.width ?? 0,
+      height: target.height ?? 0,
+    };
+  });
+}
+
+type FactsGlobal = { __sanderlingDomFacts__: () => unknown[] };
+
+(globalThis as unknown as FactsGlobal).__sanderlingDomFacts__ = domFacts;