Interfaces for execution (#2063)

* First draft for Executor interface

* Interface for execution fees custody contract

packages/contracts-communication/contracts/interfaces/IExecutionFees.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+interface IExecutionFees {
+    /// @notice Add the execution fee for a transaction. The attached value will be added to the
+    /// rewards for the executor completing the transaction.
+    /// Note: this could be used to store the execution fee for a new transaction, or to add more
+    /// funds to the execution fee of an existing transaction. Therefore this function is payable,
+    /// and does not implement any caller restrictions.
+    /// @dev Will revert if the executor is already recorded for the transaction.
+    /// @param dstChainId           The chain id of the destination chain.
+    /// @param transactionId        The id of the transaction to add the execution fee to.
+    function addExecutionFee(uint256 dstChainId, bytes32 transactionId) external payable;
+
+    /// @notice Record the executor (who completed the transaction) for a transaction,
+    /// and update the accumulated rewards for the executor.
+    /// @dev Could only be called by the Recorder.
+    /// @param dstChainId           The chain id of the destination chain.
+    /// @param transactionId        The id of the transaction to record the executor for.
+    /// @param executor             The address of the executor who completed the transaction.
+    function recordExecutor(uint256 dstChainId, bytes32 transactionId, address executor) external;
+
+    /// @notice Allows the executor to claim their unclaimed rewards.
+    /// @dev Will revert if the executor has no unclaimed rewards.
+    function claimExecutionFees() external;
+
+    // ═══════════════════════════════════════════════════ VIEWS ═══════════════════════════════════════════════════════
+
+    /// @notice Get the accumulated rewards for an executor.
+    /// @param executor             The address of the executor to get the rewards for.
+    function getAccumulatedRewards(address executor) external view returns (uint256 accumulated);
+
+    /// @notice Get the unclaimed rewards for an executor.
+    /// @param executor             The address of the executor to get the rewards for.
+    function getUnclaimedRewards(address executor) external view returns (uint256 unclaimed);
+}

packages/contracts-communication/contracts/interfaces/IExecutor.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+interface IExecutor {
+    /// @notice Request the execution of an Interchain Transaction on a remote chain.
+    /// Note: the off-chain actor needs to fetch the transaction payload from the InterchainClient
+    /// event with the same transactionId, then execute the transaction on the remote chain:
+    /// `dstInterchainClient.executeTransaction(transactionPayload)`
+    /// Once the execution is confirmed on the source chain, the off-chain actor will be able
+    /// to claim `executionFee` in the ExecutionFees contract.
+    /// @dev Could only be called by `InterchainClient` contracts.
+    /// Will revert if the execution fee is not big enough.
+    /// @param dstChainId           The chain id of the destination chain.
+    /// @param txPayloadSize        The size of the transaction payload to use for the execution.
+    /// @param transactionId        The id of the transaction to execute.
+    /// @param executionFee         The fee paid for the execution.
+    /// @param options              The options to use for the execution.
+    function requestExecution(
+        uint256 dstChainId,
+        uint256 txPayloadSize,
+        bytes32 transactionId,
+        uint256 executionFee,
+        bytes memory options
+    )
+        external;
+
+    /// @notice Get the execution fee for executing an Interchain Transaction on a remote chain.
+    /// @param dstChainId           The chain id of the destination chain.
+    /// @param txPayloadSize        The size of the transaction payload to use for the execution.
+    /// @param options              The options to use for the execution.
+    function getExecutionFee(
+        uint256 dstChainId,
+        uint256 txPayloadSize,
+        bytes memory options
+    )
+        external
+        view
+        returns (uint256);
+}