export declare class InvalidPortError extends Error {
}
/**
 * Parse the `--port` argument from a CLI argv slice (i.e. `process.argv.slice(2)`).
 *
 * Pure: does not read `process.argv`, never calls `process.exit` or `console.error`.
 * Supports both `--port <value>` (space form, checked first) and `--port=<value>`.
 *
 * @returns the parsed port, or `null` when `--port` is absent.
 * @throws {InvalidPortError} when the value is missing or out of range (integer 1–65535).
 */
export declare function parsePortArg(args: string[]): number | null;