Fix & Optimize contract

contracts/ytLp/core/YTVault.sol

@@ -17,6 +17,11 @@ import "../../interfaces/IYTPriceFeed.sol";
 contract YTVault is Initializable, UUPSUpgradeable, ReentrancyGuardUpgradeable {
     using SafeERC20 for IERC20;
     
+    /// @custom:oz-upgrades-unsafe-allow constructor
+    constructor() {
+        _disableInitializers();
+    }
+    
     error Forbidden();
     error OnlyPoolManager();
     error NotSwapper();
@@ -101,6 +106,8 @@ contract YTVault is Initializable, UUPSUpgradeable, ReentrancyGuardUpgradeable {
     );
     event EmergencyModeSet(bool enabled);
     event SwapEnabledSet(bool enabled);
+    event GovChanged(address indexed oldGov, address indexed newGov);
+    event PoolManagerChanged(address indexed oldManager, address indexed newManager);
     
     modifier onlyGov() {
         if (msg.sender != gov) revert Forbidden();
@@ -159,12 +166,16 @@ contract YTVault is Initializable, UUPSUpgradeable, ReentrancyGuardUpgradeable {
     
     function setGov(address _gov) external onlyGov {
         if (_gov == address(0)) revert InvalidAddress();
+        address oldGov = gov;
         gov = _gov;
+        emit GovChanged(oldGov, _gov);
     }
     
     function setPoolManager(address _manager) external onlyGov {
         if (_manager == address(0)) revert InvalidAddress();
+        address oldManager = ytPoolManager;
         ytPoolManager = _manager;
+        emit PoolManagerChanged(oldManager, _manager);
     }
     
     function setSwapper(address _swapper, bool _isActive) external onlyGov {
@@ -545,11 +556,12 @@ contract YTVault is Initializable, UUPSUpgradeable, ReentrancyGuardUpgradeable {
         }
         
         // 恶化平衡 → 提高手续费
-        uint256 averageDiff = (initialDiff + nextDiff) / 2;
-        if (averageDiff > targetAmount) {
-            averageDiff = targetAmount;
+        // taxBps = tax * (a + b) / (2 * target)
+        uint256 sumDiff = initialDiff + nextDiff;
+        if (sumDiff / 2 > targetAmount) {
+            sumDiff = targetAmount * 2;
         }
-        uint256 taxBps = _taxBasisPoints * averageDiff / targetAmount;
+        uint256 taxBps = _taxBasisPoints * sumDiff / (targetAmount * 2);
         return _feeBasisPoints + taxBps;
     }