export interface FrameStats {
    fps: number;
    refreshHz: number;
    dropped: number;
    late: number;
    worstMs: number;
    /** False until the calibration window completes; the HUD shows "unknown"
     * refresh and skips dropped/late instead of reading them off an interval
     * it has not measured yet. */
    calibrated: boolean;
}
/** Exported for unit tests only: `mountHud()` is the public surface. */
export declare function trackFrames(onUpdate: (stats: FrameStats) => void): () => void;
export interface LafStats {
    supported: boolean;
    blockingMs: number;
    topScript: string;
}
export declare function mountHud(): () => void;