/**
 * Decode a base64 (or data-URI) string and write it as a PNG file to
 * `uploads/<folder>/` inside the project root.
 *
 * @param base64   Raw base64 or data-URI string (e.g. "data:image/png;base64,iVBOR...")
 * @param folder   Sub-folder inside `uploads/`  (e.g. "box-return-signatures")
 * @param prefix   Filename prefix               (e.g. "sig")
 * @returns        The saved filename            (e.g. "sig-1725789123456-847231.png")
 */
export declare function saveBase64File(base64: string, folder?: string, prefix?: string): string;
/**
 * Delete a previously saved file from `uploads/<folder>/`.
 * Silently ignores missing files.
 */
export declare function deleteUploadedFile(filename: string, folder: string): void;
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