import type { WssResult } from '../types.js';
/**
 * Tests whether a WebSocket upgrade handshake can reach the target host.
 *
 * Interpretation of results:
 *
 * - 'open' event        → Full WSS connection established. Pass.
 * - 'unexpected-response' → Server replied with an HTTP status code (e.g. 502)
 *   instead of upgrading to WebSocket. This still proves the network path is
 *   open: DNS resolved, TCP connected, TLS negotiated, and an HTTP response
 *   came back. Postman's bifrost servers reject anonymous upgrade requests
 *   this way — it does NOT indicate a firewall block. Treated as pass.
 *   Caveat: a TLS-intercepting proxy could also return an HTTP error here.
 *   The response proves *something* on the network path responded, but not
 *   necessarily the origin server.
 * - Timeout             → No response to the upgrade request. Ambiguous: could
 *   be a firewall dropping packets, a proxy silently blocking upgrades, or
 *   (less likely if HTTPS passed for the same host) a server ignoring the
 *   request. Treated as fail.
 * - ECONNRESET          → Connection was forcibly closed, often by a firewall
 *   or proxy sending a TCP RST. Treated as fail.
 * - Other errors        → TLS failure, DNS (shouldn't reach here due to
 *   pipeline ordering), etc. Treated as fail.
 */
export declare function checkWss(hostname: string, timeoutMs: number): Promise<WssResult>;