/**
 * @pwngh/economy-lab
 *
 * Copyright (c) Preston Neal
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE.md file in the root directory of this source tree.
 *
 * @license MIT
 */
import type { Ctx, Operation, Outcome } from '../contract.js';
import type { Unit } from '../ports.js';
/**
 * Buys credits: the user pays real money and gets spendable credits in return. It posts twice,
 * because one posting can't mix currencies. The first posting raises the buyer's spendable CREDIT.
 * The second records the USD paid, split into backing (held in TRUST_CASH) and the buy-vs-par spread
 * (recognized as REVENUE_USD).
 *
 * @see {@link https://economy-lab-docs.pages.dev/economy/reference/operations/top-up/ Top-up} for
 *   the issuance and cash postings.
 */
export declare function topUp(operation: Operation, unit: Unit, ctx: Ctx): Promise<Outcome>;