export interface PortableWebSocketUpgradeOptions {
    readonly protocol?: string;
    readonly headers?: Headers | Record<string, string>;
    readonly idleTimeout?: number;
}
export interface PortableWebSocketUpgradeConfig {
    readonly platform: string;
    readonly runtimeName: string;
    readonly supportsNonzeroIdleTimeout?: boolean;
    readonly unsupportedIdleTimeoutDetail?: string;
    readonly supportsResponseHeaders?: boolean;
    readonly unsupportedResponseHeadersDetail?: string;
}
/**
 * Validate the portable portion of a server-side WebSocket upgrade contract.
 *
 * Native transports remain responsible for the RFC 6455 handshake itself.
 * This helper owns the behavior shared by runtimes: fail-closed request
 * detection, application header isolation, explicit subprotocol selection,
 * and deterministic idle-timeout validation.
 */
export declare function resolvePortableWebSocketUpgradeHeaders(request: Request, options: PortableWebSocketUpgradeOptions | undefined, config: PortableWebSocketUpgradeConfig): Headers;
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