import type { WebSocketServer } from "ws";
/**
 * The subset of a `ws` socket the heartbeat touches. Structural on purpose, so
 * the sweep is unit-testable with plain mock objects (no real WebSocket).
 */
interface Beating {
    isAlive?: boolean;
    ping(): void;
    terminate(): void;
}
/**
 * One heartbeat sweep, pure over the client set: a client that hasn't answered
 * the previous ping (`isAlive === false`) is considered dead and terminated;
 * every other client is pinged and marked pending until its pong flips it back.
 * Returns counts for logging/tests.
 */
export declare function heartbeatSweep(clients: Iterable<Beating>): {
    pinged: number;
    terminated: number;
};
/**
 * Keep idle WebSocket connections alive through reverse proxies. A resting
 * agent's `/ws` carries no application traffic, so nginx (`proxy_read_timeout`,
 * 60s default), Cloudflare (~100s) and friends idle-close it — and the client
 * then loops on "reconnecting" with nothing actually wrong. A periodic ping
 * resets the proxy's idle timer; a client that misses a pong (genuinely gone)
 * is terminated so it stops being pinged.
 *
 * Wires the pong→alive handshake on each connection and sweeps every
 * `intervalMs` (default well under the common 60s proxy window). Returns a stop
 * function; the timer is also cleared when the server closes.
 */
export declare function startHeartbeat(wss: WebSocketServer, intervalMs?: number): () => void;
export {};