Expose reusable builder kit surfaces and email preset pack

packages/block-editor/src/download.ts

@@ -0,0 +1,33 @@
+const downloads = new WeakMap<HTMLElement, () => void>();
+
+/** Keep a direct user-gesture fallback until replaced or the editor is removed. */
+export function offerBuilderDownload(host: HTMLElement, content: string, type: string, filename: string): void {
+  const outlet = host.querySelector<HTMLElement>("[data-builder-download]");
+  if (!outlet) throw new Error("Download outlet is unavailable");
+  const url = URL.createObjectURL(new Blob([content], { type }));
+  const link = host.ownerDocument.createElement("a");
+  link.href = url;
+  link.download = filename;
+  link.textContent = `Download prepared file: ${filename}`;
+  let disposed = false;
+  const observer = new MutationObserver(() => { if (!host.isConnected) dispose(); });
+  const dispose = () => {
+    if (disposed) return;
+    disposed = true;
+    observer.disconnect();
+    URL.revokeObjectURL(url);
+    link.remove();
+    if (downloads.get(host) === dispose) downloads.delete(host);
+  };
+  try {
+    downloads.get(host)?.();
+    outlet.replaceChildren(link);
+    observer.observe(host.ownerDocument.documentElement, { childList: true, subtree: true });
+    downloads.set(host, dispose);
+  } catch (error) {
+    dispose();
+    throw error;
+  }
+  // A blocked automatic click must not destroy the direct-click fallback.
+  try { link.click(); } catch { /* The visible link remains available. */ }
+}