/**
 * The symbol that is used to add a breadcrumb to the headers. Is an optional
 * function that is used to add a breadcrumb to the headers.
 */
export declare const ADD_BREADCRUMB: unique symbol;
/**
 * Add a crumb to the breadcrumb.
 *
 * @param {X} client Clients are somethings like viem, that we are adding breadcrumbs to, and could be owning the transport. Usually a alchemy client.
 * @param {string} crumb The crumb to add to the breadcrumb
 * @returns {Function} The updated client
 */
export declare function clientHeaderTrack<X extends {}>(client: X, crumb: string): X;