/**
 * Install (or replace) the heartbeat config. Pass `null` to stop
 * the heartbeat loop. Safe to call multiple times — the previous
 * timer is cleared before the new one starts.
 */
export declare function setHeartbeatConfig(cfg: HeartbeatConfig | null): void;
/** Read the current config — useful for tests. */
export declare function getHeartbeatConfig(): Readonly<HeartbeatState> | null;
/**
 * Manually fire a single heartbeat tick. Exposed for tests; in
 * production it's invoked by the internal interval.
 */
export declare function runOneTick(): void;
/**
 * Called from the server's pong handler (or message handler when
 * fallback `__stacks_ping__` text frames are in use). Resets the
 * missed-pong counter for the given socket so it doesn't get
 * declared dead.
 */
export declare function markPong(socket: object): void;
export declare interface HeartbeatConfig {
  intervalMs?: number
  maxMissedPongs?: number
  onDead?: (socket: unknown) => void
}
declare interface HeartbeatState {
  intervalMs: number
  maxMissedPongs: number
  onDead: (socket: unknown) => void
  missed: WeakMap<object, number>
  timer: ReturnType<typeof setInterval> | null
}