/**
 * Update check — notify-only, never auto-installs.
 *
 * Once at startup (and daily after), asks the npm registry for the latest
 * published nebula-notebook version and compares it to the running one.
 * Result is surfaced in /api/health (`update`) for the UI pill and logged
 * once to the server console. Opt out with NEBULA_NO_UPDATE_CHECK=1.
 * Network failures are silent: an update check must never affect operation.
 */
export interface UpdateInfo {
    current: string;
    latest: string | null;
    update_available: boolean;
    checked_at: number | null;
}
/** Numeric semver compare on MAJOR.MINOR.PATCH; ignores prerelease tags. */
export declare function isNewerVersion(latest: string, current: string): boolean;
export declare function startUpdateChecker(): void;
export declare function stopUpdateChecker(): void;
export declare function getUpdateInfo(): UpdateInfo;