/**
 * Shared "first stream event" deadline for model-request engines.
 *
 * A request that connects successfully but then streams zero events means the
 * transport or gateway is wedged, not slow — real models (including deep
 * thinking ones) emit their first event within seconds. Bounding this window
 * separately from any total-request deadline turns a silent multi-minute hang
 * into a fast abort-and-retry.
 */
export declare const FIRST_STREAM_EVENT_TIMEOUT_MS = 120000;
export interface FirstEventAbortController {
    readonly signal: AbortSignal;
    /** Idempotent. Call once the first real (non-keepalive) stream event arrives. */
    markFirstEvent: () => void;
    didTimeout: () => boolean;
    cleanup: () => void;
}
/**
 * Layer a first-event deadline on top of a caller's AbortSignal. Aborts if
 * `markFirstEvent()` is not called within `FIRST_STREAM_EVENT_TIMEOUT_MS`.
 * Has no opinion on a total-request deadline — callers that need one (e.g.
 * builder-engine's flat gateway timeout) compose their own on top.
 */
export declare function createFirstEventAbortController(parentSignal: AbortSignal): FirstEventAbortController;
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