chore(contracts/core): cleanup

contracts/core/.gas-snapshot

@@ -140,11 +140,11 @@ OmniPortal_xsubmit_gas_Test:test_xsubmit_guzzle5_10validators_succeeds() (gas: 2
 OmniPortal_xsubmit_gas_Test:test_xsubmit_guzzle5_25validators_succeeds() (gas: 3510011)
 OmniPortal_xsubmit_gas_Test:test_xsubmit_guzzle5_succeeds() (gas: 948663)
 Omni_Test:test_constructor() (gas: 1008119)
-Outbox_fulfill_Test:test_fulfillFee() (gas: 43845)
-Outbox_fulfill_Test:test_fulfill_succeeds() (gas: 276427)
-Outbox_fulfill_Test:test_markFulfilled_nativeMultiToken() (gas: 1125071)
-Outbox_fulfill_Test:test_markFulfilled_singleNative() (gas: 911348)
-Outbox_fulfill_Test:test_markFulfilled_singleToken() (gas: 1033779)
+Outbox_fulfill_Test:test_fulfillFee() (gas: 43429)
+Outbox_fulfill_Test:test_fulfill_succeeds() (gas: 276116)
+Outbox_fulfill_Test:test_markFulfilled_nativeMultiToken() (gas: 1123851)
+Outbox_fulfill_Test:test_markFulfilled_singleNative() (gas: 910128)
+Outbox_fulfill_Test:test_markFulfilled_singleToken() (gas: 1032559)
 PortalRegistry_Test:test_register() (gas: 1092038)
 PortalRegistry_Test:test_stub() (gas: 143)
 Preinstalls_Test:test_createX_deployCreate2_succeeds() (gas: 132705)

contracts/core/src/libraries/TypeMax.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: GPL-3.0-only
+pragma solidity ^0.8.12;
+
+/**
+ * @title TypeMax
+ * @dev Util lib with type maximum values
+ */
+library TypeMax {
+    uint256 internal constant Uint256 = type(uint256).max;
+    bytes32 internal constant Bytes32 = bytes32(Uint256);
+    address internal constant Address = address(uint160(Uint256));
+}

contracts/core/src/solve/Outbox.sol

@@ -8,6 +8,7 @@ import { XAppBase } from "../pkg/XAppBase.sol";
 
 import { SafeTransferLib } from "solady/src/utils/SafeTransferLib.sol";
 import { ConfLevel } from "../libraries/ConfLevel.sol";
+import { TypeMax } from "../libraries/TypeMax.sol";
 import { Solve } from "./Solve.sol";
 
 import { IInbox } from "./interfaces/IInbox.sol";
@@ -43,35 +44,16 @@ contract Outbox is OwnableRoles, ReentrancyGuard, Initializable, XAppBase {
     uint256 internal constant SOLVER = _ROLE_0;
 
     /**
-     * @notice Gas limit for the callback.
+     * @notice Gas limit for Inbox.markFulfilled callback.
      */
-    uint64 internal constant CALLBACK_GAS_LIMIT = 200_000;
+    uint64 internal constant MARK_FULFILLED_GAS_LIMIT = 100_000;
 
     /**
-     * @notice Placeholder for request ID.
+     * @notice Stubbed calldata for Inbox.markFulfilled. Used to estimate the gas cost.
+     * @dev Type maxes used to ensure no non-zero bytes in fee estimation.
      */
-    bytes32 internal constant ID_PLACEHOLDER = bytes32(type(uint256).max);
-
-    /**
-     * @notice Placeholder for call hash.
-     */
-    bytes32 internal constant CALLHASH_PLACEHOLDER = bytes32(type(uint256).max);
-
-    /**
-     * @notice Placeholder for solver address.
-     */
-    address internal constant SOLVER_PLACEHOLDER = address(type(uint160).max);
-
-    /**
-     * @notice Signature of the markFulfilled function.
-     */
-    string internal constant MARK_FULFILLED_SIGNATURE = "markFulfilled(bytes32,bytes32,address)";
-
-    /**
-     * @notice Encoded call data for the markFulfilled function.
-     */
-    bytes internal constant MARK_FULFILLED_CALLDATA =
-        abi.encodeWithSignature(MARK_FULFILLED_SIGNATURE, ID_PLACEHOLDER, CALLHASH_PLACEHOLDER, SOLVER_PLACEHOLDER);
+    bytes internal constant MARK_FULFILLED_STUB_CDATA =
+        abi.encodeCall(IInbox.markFulfilled, (TypeMax.Bytes32, TypeMax.Bytes32, TypeMax.Address));
 
     /**
      * @notice Address of the inbox contract.
@@ -107,7 +89,7 @@ contract Outbox is OwnableRoles, ReentrancyGuard, Initializable, XAppBase {
      * @param sourceChainId ID of the source chain.
      */
     function fulfillFee(uint64 sourceChainId) public view returns (uint256) {
-        return feeFor(sourceChainId, MARK_FULFILLED_CALLDATA, CALLBACK_GAS_LIMIT);
+        return feeFor(sourceChainId, MARK_FULFILLED_STUB_CDATA, MARK_FULFILLED_GAS_LIMIT);
     }
 
     /**
@@ -172,7 +154,7 @@ contract Outbox is OwnableRoles, ReentrancyGuard, Initializable, XAppBase {
 
         // Send the fulfillment call to the inbox
         bytes memory data = abi.encodeCall(IInbox.markFulfilled, (reqId, callHash, creditTo));
-        uint256 fee = xcall(sourceChainId, ConfLevel.Finalized, _inbox, data, CALLBACK_GAS_LIMIT);
+        uint256 fee = xcall(sourceChainId, ConfLevel.Finalized, _inbox, data, MARK_FULFILLED_GAS_LIMIT);
         if (msg.value - call.value < fee) revert InsufficientFee();
 
         emit Fulfilled(reqId, callHash, creditTo);