/**
 * Resolve a user-supplied `--cache-dir` value into an absolute path.
 *
 * When `cacheDir` is absent or empty, returns `undefined` so callers fall
 * through to the `TTSC_CACHE_DIR` environment variable and the workspace-local
 * default handled inside `buildSourcePlugin`. When `cacheDir` is already
 * absolute it is returned unchanged; otherwise it is resolved relative to
 * `cwd`.
 */
export declare function resolveCacheDir(cwd: string, cacheDir?: string): string | undefined;