/**
 * Loads the subscription forms widget (an ES module that registers the
 * <pushwoosh-subscribe-widget> custom element) exactly once per page.
 * Resolves when the custom element is defined.
 *
 * The wait is bounded by a timeout: a script that loads but throws during
 * evaluation never registers the element and never fires the script `error`
 * event, so `customElements.whenDefined()` alone would hang forever (and with
 * it the whole web popups pipeline). On failure the memoized promise is reset
 * so the next popup can retry.
 */
export declare function ensureSubscriptionFormsWidgetLoaded(): Promise<void>;