fix(contracts): check for sufficient msgValue for AggregationHook

solidity/contracts/hooks/aggregation/StaticAggregationHook.sol

@@ -13,11 +13,19 @@ pragma solidity >=0.8.0;
  @@@@@@@@@       @@@@@@@@@
 @@@@@@@@@       @@@@@@@@*/
 
+// ============ Internal Imports ============
+import {StandardHookMetadata} from "../libs/StandardHookMetadata.sol";
 import {AbstractPostDispatchHook} from "../libs/AbstractPostDispatchHook.sol";
 import {IPostDispatchHook} from "../../interfaces/hooks/IPostDispatchHook.sol";
 import {MetaProxy} from "../../libs/MetaProxy.sol";
 
+// ============ External Imports ============
+import {Address} from "@openzeppelin/contracts/utils/Address.sol";
+
 contract StaticAggregationHook is AbstractPostDispatchHook {
+    using StandardHookMetadata for bytes;
+    using Address for address payable;
+
     // ============ External functions ============
 
     /// @inheritdoc IPostDispatchHook
@@ -32,17 +40,26 @@ contract StaticAggregationHook is AbstractPostDispatchHook {
     ) internal override {
         address[] memory _hooks = hooks(message);
         uint256 count = _hooks.length;
+        uint256 gasRemaining = msg.value;
         for (uint256 i = 0; i < count; i++) {
             uint256 quote = IPostDispatchHook(_hooks[i]).quoteDispatch(
                 metadata,
                 message
             );
 
+            gasRemaining -= quote;
             IPostDispatchHook(_hooks[i]).postDispatch{value: quote}(
                 metadata,
                 message
             );
         }
+
+        if (gasRemaining > 0) {
+            address payable refundAddress = payable(
+                metadata.refundAddress(msg.sender)
+            );
+            refundAddress.sendValue(gasRemaining);
+        }
     }
 
     /// @inheritdoc AbstractPostDispatchHook

solidity/test/hooks/AggregationHook.t.sol

@@ -72,6 +72,35 @@ contract AggregationHookTest is Test {
         hook.postDispatch{value: _msgValue}("", message);
     }
 
+    function test_postDispatch_refundsExcess(uint8 _hooks) public {
+        uint256 fee = PER_HOOK_GAS_AMOUNT;
+        address[] memory hooksDeployed = deployHooks(_hooks, fee);
+        uint256 requiredValue = hooksDeployed.length * fee;
+        uint256 overpaidValue = requiredValue + 1000;
+
+        vm.prank(address(this));
+
+        uint256 initialBalance = address(this).balance;
+
+        bytes memory message = abi.encodePacked("hello world");
+        hook.postDispatch{value: overpaidValue}("", message);
+
+        assertEq(address(hook).balance, 0);
+        assertEq(address(this).balance, initialBalance - requiredValue);
+    }
+
+    function testPostDispatch_preventsUsingContractFunds(uint8 _hooks) public {
+        vm.assume(_hooks > 0);
+
+        // aggregation hook has left over funds
+        uint256 additionalFunds = 1 ether;
+        vm.deal(address(hook), additionalFunds);
+
+        bytes memory message = abi.encodePacked("hello world");
+        vm.expectRevert(); // underflow
+        hook.postDispatch{value: 0}("", message);
+    }
+
     function testQuoteDispatch(uint8 _hooks) public {
         uint256 fee = PER_HOOK_GAS_AMOUNT;
         address[] memory hooksDeployed = deployHooks(_hooks, fee);
@@ -94,4 +123,6 @@ contract AggregationHookTest is Test {
         deployHooks(1, 0);
         assertEq(hook.hookType(), uint8(IPostDispatchHook.Types.AGGREGATION));
     }
+
+    receive() external payable {}
 }