import type { OneSubErrorCode } from '@onesub/shared';
/** Type guard for a string being a canonical `OneSubErrorCode`. */
export declare function isOneSubErrorCode(x: unknown): x is OneSubErrorCode;
/**
 * Structured error thrown by the SDK. Consumers branch on `.code`
 * (a value from `ONESUB_ERROR_CODE`) for programmatic handling.
 */
export declare class OneSubError extends Error {
    readonly code: OneSubErrorCode;
    constructor(code: OneSubErrorCode, message?: string, cause?: unknown);
}
export declare function isOneSubError(err: unknown): err is OneSubError;
/**
 * Wrap any thrown value into a `OneSubError`. Values that already carry a
 * canonical `.code` are preserved; everything else falls back to
 * `INTERNAL_ERROR` (or the provided default).
 */
export declare function toOneSubError(err: unknown, fallbackCode?: OneSubErrorCode): OneSubError;
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