/**
 * Converts UTF-8 text to GBK encoded Base64 string
 *
 * This is required for Chinese characters in print content according to Memobird API documentation.
 * The API expects Chinese text to be GBK encoded before Base64 conversion.
 *
 * @param text - UTF-8 text to convert
 * @returns GBK Base64 encoded string
 * @throws {ValidationError} If encoding fails
 *
 * @example
 * ```typescript
 * const encoded = textToGBKBase64('你好世界');
 * console.log(encoded); // Outputs GBK Base64 string
 * ```
 */
export declare function textToGBKBase64(text: string): string;
/**
 * Decodes GBK Base64 string back to UTF-8 text
 *
 * @param gbkBase64 - GBK Base64 encoded string
 * @returns UTF-8 decoded text
 * @throws {ValidationError} If decoding fails
 *
 * @example
 * ```typescript
 * const decoded = gbkBase64ToText(encodedString);
 * console.log(decoded); // Outputs: '你好世界'
 * ```
 */
export declare function gbkBase64ToText(gbkBase64: string): string;
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