/**
 * When the access token in a credential file expires, as epoch ms, or 0 when
 * the file is missing, unreadable, or carries no expiry.
 *
 * Zero rather than null so freshness comparisons stay plain arithmetic: an
 * unknown expiry loses to any known one, which is the safe direction (a copy
 * we cannot date is never treated as the newer one).
 */
export declare function readExpiresAt(credentialsFile: string): number;