import type { WebSocket } from "ws";
/** Interval between heartbeat sweeps. ~30s is the standard NAT/proxy keep-alive floor. */
export declare const WS_HEARTBEAT_INTERVAL_MS = 30000;
/** Minimal shape we need from a ws socket for liveness tracking. */
export interface HeartbeatSocket {
    isAlive?: boolean;
    readyState: number;
    ping(): void;
    terminate(): void;
}
/**
 * Mark a freshly-connected socket alive and refresh its liveness on every pong.
 * Call once per new connection.
 */
export declare function trackHeartbeat(ws: HeartbeatSocket & {
    on(event: "pong", cb: () => void): void;
}): void;
/**
 * Run one heartbeat sweep over a set of sockets:
 *   - terminate() any socket still marked dead from the previous sweep
 *   - otherwise mark it provisionally dead and ping() it; the pong handler
 *     (installed by trackHeartbeat) flips it back to alive before the next sweep.
 * Returns counts for logging/testing.
 */
export declare function sweepHeartbeat(sockets: Iterable<HeartbeatSocket>): {
    terminated: number;
    pinged: number;
};
/**
 * Start a periodic heartbeat across one or more WebSocketServer-like objects
 * (anything exposing a `clients` Set). Returns a stop function that clears the
 * timer. The timer is unref()'d so it never keeps the process alive.
 */
export declare function startWsHeartbeat(servers: Array<{
    clients: Set<WebSocket>;
}>, opts?: {
    intervalMs?: number;
    onSweep?: (result: {
        terminated: number;
        pinged: number;
    }) => void;
}): () => void;
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