/**
 * Reads the reason why a harness refused to work because it is not logged in, from its raw CLI output.
 *
 * Messages the harness reports in machine-readable output are preferred over its raw output lines, so the
 * reason is the sentence the harness wrote for a human and not the JSON event which transported it.
 *
 * @returns One short single-line reason, or `undefined` when the failure was not caused by authentication.
 */
export declare function extractHarnessAuthenticationFailureReason(harnessOutput: string): string | undefined;