/**
 * Start a tunnel via srv.us using SSH.
 *
 * srv.us requires:
 *  - SSH client installed (built-in on Windows 10+, macOS, Linux)
 *  - An SSH key (ed25519 recommended)
 *
 * No account needed. URLs are derived from your SSH key.
 * If your SSH key is on GitHub, you also get: https://<github-user>.gh.srv.us
 *
 * The `subdomain` parameter is used as the SSH username (GitHub login)
 * to get a vanity URL like https://<subdomain>.gh.srv.us
 *
 * The `sshkey` parameter specifies which SSH private key to use.
 * Can be a full path or just the key name (e.g. "id_personal" -> ~/.ssh/id_personal).
 */
export declare function startSrvusTunnel(port: number, subdomain?: string, sshkey?: string): Promise<string>;