/**
 * Idle heartbeat for the realtime WebSocket connection (subscription-v2.ts).
 *
 * A socket whose server has stopped delivering frames looks exactly like a
 * quiet one: the browser reports it open and nothing arrives. The client only
 * learns the difference by asking. Once nothing has been received for
 * HEARTBEAT_IDLE_MS the heartbeat asks the connection to send a ping; if
 * nothing at all arrives within HEARTBEAT_TIMEOUT_MS after that, the socket is
 * declared dead and the connection is reconnected. Any inbound frame counts as
 * proof of life, so a busy socket is never pinged and a pong is just another
 * frame. The connection may decline to ping (it already has a request in
 * flight with its own timeout); the idle wait then simply starts over.
 *
 * The timeout sits above both budgets a pong can wait behind: the connection's
 * own 30 s request budget (the server handles one frame per socket at a time)
 * and the object's 30 s CPU slice, which another socket's handler can hold
 * while every pong waits. A healthy socket must never be declared dead
 * within either.
 *
 * Pure: timers come from the clock passed in, so tests can drive it.
 */
export declare const HEARTBEAT_IDLE_MS = 25000;
export declare const HEARTBEAT_TIMEOUT_MS = 45000;
export interface HeartbeatClock {
    setTimeout(callback: () => void, ms: number): unknown;
    clearTimeout(handle: unknown): void;
}
export declare class SocketHeartbeat {
    /** Send a ping now; return false to skip this round (the idle wait restarts). */
    private readonly sendPing;
    private readonly onDead;
    private readonly clock;
    private readonly idleMs;
    private readonly timeoutMs;
    private idleTimer;
    private timeoutTimer;
    private stopped;
    constructor(
    /** Send a ping now; return false to skip this round (the idle wait restarts). */
    sendPing: () => boolean, onDead: () => void, clock?: HeartbeatClock, idleMs?: number, timeoutMs?: number);
    start(): void;
    /** An inbound frame arrived: the socket is alive, so the idle wait starts over. */
    noteActivity(): void;
    stop(): void;
    private armIdle;
    private clearTimers;
}