/**
 * Builds one normalized filename for a chat export download.
 *
 * @param title - Human-readable chat title.
 * @param fileExtension - Output file extension without a leading dot.
 * @param date - Export date used in the filename.
 * @returns Stable filename suitable for browser downloads and HTTP headers.
 *
 * @private Internal helper shared by chat export flows.
 */
export declare function createChatExportFilename(title: string, fileExtension: string, date?: Date): string;