/** Lightweight metrics collector: counters, timings, and derived rates.
 *  Chat/embed classes feed it automatically; read `summary()` any time or
 *  subscribe to the owning class's 'metric' hook. */
export interface MetricEvent {
    name: string;
    value: number;
    unit: 'ms' | 'count' | 'tokens' | 'tokens/s';
}
export declare class Metrics {
    counters: Map<string, number>;
    timings: Map<string, number[]>;
    count(name: string, by?: number): void;
    time(name: string, ms: number): void;
    /** Time an async operation and record it under name. */
    measure<T>(name: string, fn: () => Promise<T>): Promise<T>;
    summary(): Record<string, number>;
    reset(): void;
}