/**
 * Append only missing lines to an existing text file, preserving any existing
 * user-managed content.
 *
 * @param filePath Absolute file path to append.
 * @param lines Lines that should be present in the file.
 * @returns A promise that resolves after the file is created or updated.
 */
export declare function appendMissingLines(filePath: string, lines: readonly string[]): Promise<void>;
/**
 * Write a generated file only when it is absent, recording a preservation
 * warning when the target already exists.
 *
 * @param options File write options.
 * @param options.filePath Absolute target file path.
 * @param options.source Generated source to write when absent.
 * @param options.warnings Mutable warning collection for preserved files.
 * @returns A promise that resolves after the file is written or preserved.
 */
export declare function writeFileIfAbsent({ filePath, source, warnings }: {
    filePath: string;
    source: string;
    warnings: string[];
}): Promise<void>;
/**
 * Write a newly generated scaffold file and fail if the target already exists.
 *
 * @param filePath Absolute target file path.
 * @param source Generated source to write.
 * @returns A promise that resolves after the file is written.
 * @throws {Error} When the scaffold target already exists.
 */
export declare function writeNewScaffoldFile(filePath: string, source: string): Promise<void>;