/**
 * withFallback — provider decorator that falls back to a secondary
 * on error.
 *
 * Pattern: Decorator (GoF) — composes two `LLMProvider`s into one.
 * Role:    Outer ring (Hexagonal). Stacks with `withRetry`:
 *          `withRetry(withFallback(primary, fallback))` first retries
 *          the primary, then on exhaustion falls back to the secondary.
 *
 * Common pairings:
 *   • Anthropic primary, OpenAI fallback (vendor outage tolerance)
 *   • Real provider primary, Mock fallback (degrade gracefully in dev)
 *   • Premium model primary, cheaper model fallback (cost ceiling)
 *
 * `stream()` falls back too — if the primary's stream errors before
 * yielding any chunks, we restart on the fallback. Once the primary
 * has yielded chunks the stream is committed — fallback would
 * duplicate the partial output.
 */
import type { LLMProvider } from '../adapters/types.js';
export interface WithFallbackOptions {
    /**
     * Predicate to decide whether an error from the primary should
     * trigger fallback. Default: every error except AbortError.
     * Override to gate on specific status codes or error types.
     */
    readonly shouldFallback?: (error: unknown) => boolean;
    /**
     * Hook invoked when the primary fails and we're about to call the
     * fallback. Useful for logging in standalone (non-agentfootprint) use.
     *
     * You do NOT need this to get fallback telemetry inside a run: since
     * v7.8 the in-run LLM call sites hand this decorator an `LLMCallHooks`
     * and translate its reports into `agentfootprint.fallback.triggered`
     * events, stamped with the real `runId`/`runtimeStageId`. This hook is
     * the consumer-owned escape hatch and its contract is unchanged.
     */
    readonly onFallback?: (error: unknown) => void;
}
/**
 * Wrap a primary provider with a fallback. Tries primary first; on
 * error matching the policy, calls the fallback.
 *
 * @example
 *   const provider = withFallback(
 *     anthropic({ apiKey: A }),
 *     openai({ apiKey: O }),
 *     { onFallback: (err) => console.warn('primary failed, falling back:', err) },
 *   );
 */
export declare function withFallback(primary: LLMProvider, fallback: LLMProvider, options?: WithFallbackOptions): LLMProvider;
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