Reuse preview sanitizer across client page bundles

packages/block-editor/src/preview-html.ts

@@ -1,14 +1,17 @@
 import createDOMPurify from "dompurify";
 
-const sanitizers = new WeakMap<object, ReturnType<typeof createDOMPurify>>();
+// Page modules are bundled separately. Keep the sanitizer on the realm so SPA
+// navigation reuses its Trusted Types policy instead of creating it twice.
+const sanitizerKey = Symbol.for("wrnexus.block-editor.preview-sanitizer");
+type PreviewRealm = Window & { [sanitizerKey]?: ReturnType<typeof createDOMPurify> };
 /** Sanitize generated previews in the sink's realm, including Trusted Types. */
 export function builderPreviewHTML(html: string, doc: Document = document): string {
   const realm = doc.defaultView;
   if (!realm) throw new Error("Preview document has no browser realm");
-  let sanitizer = sanitizers.get(realm);
+  let sanitizer = (realm as PreviewRealm)[sanitizerKey];
   if (!sanitizer) {
     sanitizer = createDOMPurify(realm);
-    sanitizers.set(realm, sanitizer);
+    Object.defineProperty(realm, sanitizerKey, { value: sanitizer });
   }
   return sanitizer.sanitize(html, {
     WHOLE_DOCUMENT: true,