/**
 * Check if an error is retryable (429/500/503 or overloaded).
 */
export declare function isRetryable(error: unknown): boolean;
/**
 * Check if an error is a config error that should NOT trigger fallback.
 * Returns true for 400/401/403 errors.
 */
export declare function isConfigError(error: unknown): boolean;
/**
 * Sleep utility for retry delays.
 */
export declare function sleep(ms: number): Promise<void>;
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