feat: Refactor callback to use transient storage

With this, we don't need the univ3 specific method in the router contract. This should be flexible enough for most protocols that integrate

TODO: is this safe enough??

--- don't change below this line ---
ENG-4411 Took 1 hour 52 minutes

Took 4 minutes

Took 5 minutes

foundry/src/Dispatcher.sol

@@ -52,7 +52,7 @@ contract Dispatcher {
      * @dev Calls an executor, assumes swap.protocolData contains
      *  protocol-specific data required by the executor.
      */
-    // slither-disable-next-line delegatecall-loop
+    // slither-disable-next-line delegatecall-loop,assembly
     function _callExecutor(
         address executor,
         uint256 amount,
@@ -62,6 +62,10 @@ contract Dispatcher {
             revert Dispatcher__UnapprovedExecutor();
         }
 
+        assembly {
+            tstore(0, executor)
+        }
+
         // slither-disable-next-line controlled-delegatecall,low-level-calls
         (bool success, bytes memory result) = executor.delegatecall(
             abi.encodeWithSelector(IExecutor.swap.selector, amount, data)
@@ -80,8 +84,12 @@ contract Dispatcher {
         calculatedAmount = abi.decode(result, (uint256));
     }
 
+    // slither-disable-next-line assembly
     function _handleCallback(bytes calldata data) internal {
-        address executor = address(uint160(bytes20(data[data.length - 20:])));
+        address executor;
+        assembly {
+            executor := tload(0)
+        }
 
         if (!executors[executor]) {
             revert Dispatcher__UnapprovedExecutor();

foundry/src/TychoRouter.sol

@@ -502,26 +502,6 @@ contract TychoRouter is AccessControl, Dispatcher, Pausable, ReentrancyGuard {
         require(msg.sender.code.length != 0);
     }
 
-    /**
-     * @dev Called by UniswapV3 pool when swapping on it.
-     * See in IUniswapV3SwapCallback for documentation.
-     */
-    function uniswapV3SwapCallback(
-        int256, /* amount0Delta */
-        int256, /* amount1Delta */
-        bytes calldata data
-    ) external {
-        if (data.length < 24) revert TychoRouter__InvalidDataLength();
-        // We are taking advantage of the fact that the data we need is already encoded in the correct format inside msg.data
-        // This way we preserve the bytes calldata (and don't need to convert it to bytes memory)
-        uint256 dataOffset = 4 + 32 + 32 + 32; // Skip selector + 2 ints + data_offset
-        uint256 dataLength =
-            uint256(bytes32(msg.data[dataOffset:dataOffset + 32]));
-
-        bytes calldata fullData = msg.data[4:dataOffset + 32 + dataLength];
-        _handleCallback(fullData);
-    }
-
     /**
      * @dev Called by PancakeV3 pool when swapping on it.
      */

foundry/src/executors/UniswapV3Executor.sol

@@ -80,6 +80,7 @@ contract UniswapV3Executor is IExecutor, ICallback {
         returns (bytes memory result)
     {
         // The data has the following layout:
+        // - selector (4 bytes)
         // - amount0Delta (32 bytes)
         // - amount1Delta (32 bytes)
         // - dataOffset (32 bytes)
@@ -87,11 +88,11 @@ contract UniswapV3Executor is IExecutor, ICallback {
         // - protocolData (variable length)
 
         (int256 amount0Delta, int256 amount1Delta) =
-            abi.decode(msgData[:64], (int256, int256));
+            abi.decode(msgData[4:68], (int256, int256));
 
-        address tokenIn = address(bytes20(msgData[128:148]));
+        address tokenIn = address(bytes20(msgData[132:152]));
 
-        verifyCallback(msgData[128:]);
+        verifyCallback(msgData[132:]);
 
         uint256 amountOwed =
             amount0Delta > 0 ? uint256(amount0Delta) : uint256(amount1Delta);
@@ -147,10 +148,10 @@ contract UniswapV3Executor is IExecutor, ICallback {
 
     function _makeV3CallbackData(address tokenIn, address tokenOut, uint24 fee)
         internal
-        view
+        pure
         returns (bytes memory)
     {
-        return abi.encodePacked(tokenIn, tokenOut, fee, self);
+        return abi.encodePacked(tokenIn, tokenOut, fee);
     }
 
     function _verifyPairAddress(

foundry/src/executors/UniswapV4Executor.sol

@@ -41,7 +41,6 @@ contract UniswapV4Executor is IExecutor, V4Router, ICallback {
             address tokenIn,
             address tokenOut,
             bool zeroForOne,
-            address callbackExecutor,
             UniswapV4Executor.UniswapV4Pool[] memory pools
         ) = _decodeData(data);
 
@@ -107,14 +106,13 @@ contract UniswapV4Executor is IExecutor, V4Router, ICallback {
             params[2] = abi.encode(Currency.wrap(tokenOut), uint256(0));
             swapData = abi.encode(actions, params);
         }
-        bytes memory fullData = abi.encodePacked(swapData, callbackExecutor);
         uint256 tokenOutBalanceBefore;
 
         tokenOutBalanceBefore = tokenOut == address(0)
             ? address(this).balance
             : IERC20(tokenOut).balanceOf(address(this));
 
-        executeActions(fullData);
+        executeActions(swapData);
 
         uint256 tokenOutBalanceAfter;
 
@@ -140,22 +138,20 @@ contract UniswapV4Executor is IExecutor, V4Router, ICallback {
             address tokenIn,
             address tokenOut,
             bool zeroForOne,
-            address callbackExecutor,
             UniswapV4Pool[] memory pools
         )
     {
-        if (data.length < 87) {
+        if (data.length < 67) {
             revert UniswapV4Executor__InvalidDataLength();
         }
 
         tokenIn = address(bytes20(data[0:20]));
         tokenOut = address(bytes20(data[20:40]));
         zeroForOne = (data[40] != 0);
-        callbackExecutor = address(bytes20(data[41:61]));
 
-        uint256 poolsLength = (data.length - 61) / 26; // 26 bytes per pool object
+        uint256 poolsLength = (data.length - 41) / 26; // 26 bytes per pool object
         pools = new UniswapV4Pool[](poolsLength);
-        bytes memory poolsData = data[61:];
+        bytes memory poolsData = data[41:];
         uint256 offset = 0;
         for (uint256 i = 0; i < poolsLength; i++) {
             address intermediaryToken;