/**
 * Why an upstream call failed (DES-MCP-TOOLS-001 §6 steps 6-7). Its own module so the MCP invoker
 * (`invoke.ts`) and the REST invoker (`rest.ts`) share it without importing each other at load.
 */
/** Why an upstream call failed. `boundary` = a `rest` request would have left its pinned host (I6). */
export type UpstreamErrorClass = 'transport' | 'timeout' | 'http' | 'protocol' | 'boundary';
export declare class UpstreamCallError extends Error {
    readonly errorClass: UpstreamErrorClass;
    readonly retryable: boolean;
    constructor(errorClass: UpstreamErrorClass, retryable: boolean, message: string);
}
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