import type { ServerResponse } from 'node:http';
export type SseKeepalive = {
    stop: () => void;
};
/**
 * Wraps res.writeHead so that, the moment the transport starts an SSE response
 * (status 200 + Content-Type: text/event-stream), headers are flushed immediately
 * (so intermediary proxies like CloudFront receive them before their origin
 * response timeout) and SSE comment pings are written on an interval.
 *
 * Returns a handle whose stop() clears the timer; it also auto-stops on the
 * response's 'finish'/'close'/'error' events.
 */
export declare function attachSseKeepalive(res: ServerResponse, intervalMs?: number): SseKeepalive;
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