> ## Documentation Index
> Fetch the complete documentation index at: https://docs.utexo.com/llms.txt
> Use this file to discover all available pages before exploring further.

# EVM and Tron Settlement

> Deploy resolver executors and settle Utexo swaps on EVM chains and Tron, including single-chain, cross-chain, DEX, and fast refund paths.

Utexo supports four settlement paths on EVM:

* Cross-chain swap
* Cross-chain swap with DEX
* Single-chain atomic swap
* Fast refund

Users sign Permit2 approvals. The resolver submits every on-chain transaction and pays gas.

## Onboarding

A protocol administrator registers each resolver in the `ResolversWhitelist` contract with:

* Executor contract address
* `depositAddresses` allow list
* `withdrawAddresses` allow list

The same resolver must own the authorized deposit and withdraw roles. The on-chain `checkSameResolver` check enforces this.

## Executor contract

Each resolver deploys an Executor implementing the `IExecutor` interface:

```solidity theme={null}
function fulfill(
  address token,
  uint256 minAmount,
  uint256 maxAmount,
  bytes data
) external returns (uint256 amount);

function swap(
  address outputToken,
  uint256 minOutputAmount,
  uint256 maxOutputAmount,
  address inputToken,
  uint256 inputAmount,
  bytes data
) external returns (uint256 amount);

function dexSwap(
  address outputToken,
  uint256 minOutputAmount,
  uint256 maxOutputAmount,
  address inputToken,
  uint256 inputAmount,
  bytes data
) external returns (uint256 amount);
```

The protocol verifies that its own ERC-20 balance increased by exactly the amount returned by `IExecutor`.

### Method responsibilities

* `fulfill` transfers between `minAmount` and `maxAmount` to the caller and returns the actual transferred amount.
* `swap` receives input tokens already transferred to the Executor and returns a bounded output to `EscrowRouter`.
* `dexSwap` uses only deposited user tokens with non-empty routing `data`.

<Warning>
  `dexSwap` must trade the deposited user tokens through the DEX. Do not fund the output from your own treasury liquidity.
</Warning>

## Fulfillment contract

The protocol deploys a Fulfillment contract once per resolver per destination chain. The resolver supplies:

* Executor address
* Authorized caller/operator addresses

## Cross-chain swap

<Steps>
  <Step title="Deposit">
    `EscrowRouter.deposit` deploys a deterministic CREATE2 proxy and transfers the user's input tokens into it using Permit2.
  </Step>

  <Step title="Fulfill">
    On the destination chain, the resolver's Executor `fulfill` pays the user the destination amount within `[minAmount, maxAmount]`.
  </Step>

  <Step title="Withdraw">
    After Utexo verifies fulfillment and reveals the secret, the resolver withdraws from the source-chain escrow.
  </Step>
</Steps>

<Note>
  The source does not fully document the withdraw signature and parameters. See [Validation Gaps](/product-suite/swap/resolver-integration/validation-gaps).
</Note>

## Cross-chain swap with DEX

Source-chain deposit transfers the user's input token to the Executor, calls `dexSwap`, validates the output against the declared bounds, and locks the resulting `tokenOut` in the proxy. The follow-on Order then uses `tokenOut` and `minAmountOut` on the destination.

## Single-chain atomic swap

`EscrowRouter.swap` atomically transfers the user's input to the Executor and sends a bounded output amount directly to the user. When the destination token is native ETH, the Executor supplies WETH and the protocol unwraps it before paying the user.

## Fast refund

Backend and resolver co-sign the following EIP-712 message in the `EscrowImplementation` domain:

```text theme={null}
FastRefund(bytes32 orderHash)
```

The resolver signer must match `order.resolverDeposit`.

## Tron

Tron is architecturally aligned with EVM but uses TIP-712 with these differences:

* No `version` field in the domain.
* Domain type string: `EIP712Domain(string name,uint256 chainId,address verifyingContract)`.
* `chainId` is masked with `chainId & 0xffffffff`.

These rules apply to the deposit witness, fulfillment, and refund signing.