/**
 * Return the current UTC instant as an ISO Instant string.
 *
 * - Uses Temporal.Now.instant() to get current UTC time.
 * - Returns "" on failure.
 *
 * @returns ISO Instant string (e.g. "2024-02-29T00:00:00Z") or "" on failure
 *
 * @example getUtcNow() // "2024-02-29T00:00:00Z"
 * @example getUtcNow() // "" (on failure)
 */
export declare function getUtcNow(): string;