/**
 * Truncate `filename` to fit within `maxChars` by inserting `...` near the
 * middle while preserving the file extension. If the filename already fits,
 * returns it unchanged. If the extension alone exceeds the budget, the
 * extension is dropped and the head is truncated.
 *
 * The utility operates on Unicode code points (after NFC normalization), so
 * Hangul syllables stay intact even when the input is decomposed jamo (as
 * macOS produces), and surrogate pairs (emoji, supplementary CJK) are never
 * split. The caller is responsible for picking a `maxChars` that fits the
 * rendered container.
 *
 * Examples:
 *   truncateMiddleKeepExtension('File-name-is-too-long.pdf', 14) -> 'File...ong.pdf'
 *   truncateMiddleKeepExtension('short.pdf', 14)                 -> 'short.pdf'
 *   truncateMiddleKeepExtension('noextension', 14)               -> 'noextension'
 *   truncateMiddleKeepExtension('verylong.tar.gz', 10)           -> 've...tar.gz'
 *   truncateMiddleKeepExtension('long', 3)                       -> '...'
 */
export declare function truncateMiddleKeepExtension(filename: string, maxChars: number): string;