feat: Rebate on distribution

script/DeployBase.s.sol

@@ -168,7 +168,8 @@ abstract contract DeployBase is Script {
             CSFeeDistributor feeDistributorImpl = new CSFeeDistributor({
                 stETH: locator.lido(),
                 accounting: address(accounting),
-                oracle: address(oracle)
+                oracle: address(oracle),
+                rebateRecipient: config.aragonAgent
             });
             feeDistributor = CSFeeDistributor(
                 _deployProxy(config.proxyAdmin, address(feeDistributorImpl))

script/DeployImplementationsBase.s.sol

@@ -62,7 +62,8 @@ abstract contract DeployImplementationsBase is DeployBase {
             CSFeeDistributor feeDistributorImpl = new CSFeeDistributor({
                 stETH: locator.lido(),
                 accounting: address(accounting),
-                oracle: address(oracle)
+                oracle: address(oracle),
+                rebateRecipient: config.aragonAgent
             });
 
             verifier = new CSVerifier({

src/CSFeeDistributor.sol

@@ -24,6 +24,7 @@ contract CSFeeDistributor is
     IStETH public immutable STETH;
     address public immutable ACCOUNTING;
     address public immutable ORACLE;
+    address public immutable REBATE_RECIPIENT;
 
     /// @notice The latest Merkle Tree root
     bytes32 public treeRoot;
@@ -46,14 +47,21 @@ contract CSFeeDistributor is
     /// @notice The number of _distributionDataHistory records
     uint256 public distributionDataHistoryCount;
 
-    constructor(address stETH, address accounting, address oracle) {
+    constructor(
+        address stETH,
+        address accounting,
+        address oracle,
+        address rebateRecipient
+    ) {
         if (accounting == address(0)) revert ZeroAccountingAddress();
         if (oracle == address(0)) revert ZeroOracleAddress();
         if (stETH == address(0)) revert ZeroStEthAddress();
+        if (rebateRecipient == address(0)) revert ZeroRebateRecipientAddress();
 
         ACCOUNTING = accounting;
         STETH = IStETH(stETH);
         ORACLE = oracle;
+        REBATE_RECIPIENT = rebateRecipient;
 
         _disableInitializers();
     }
@@ -97,11 +105,12 @@ contract CSFeeDistributor is
         string calldata _treeCid,
         string calldata _logCid,
         uint256 _distributedShares,
+        uint256 rebateShares,
         uint256 refSlot
     ) external {
         if (msg.sender != ORACLE) revert NotOracle();
         if (
-            totalClaimableShares + _distributedShares >
+            totalClaimableShares + _distributedShares + rebateShares >
             STETH.sharesOf(address(this))
         ) {
             revert InvalidShares();
@@ -131,6 +140,11 @@ contract CSFeeDistributor is
 
         emit ModuleFeeDistributed(_distributedShares);
 
+        if (rebateShares > 0) {
+            STETH.transferShares(REBATE_RECIPIENT, rebateShares);
+            emit RebateTransferred(rebateShares);
+        }
+
         // NOTE: Make sure off-chain tooling provides a distinct CID of a log even for empty reports, e.g. by mixing
         // in a frame identifier such as reference slot to a file.
         if (bytes(_logCid).length == 0) revert InvalidLogCID();
@@ -147,7 +161,8 @@ contract CSFeeDistributor is
             treeRoot: treeRoot,
             treeCid: treeCid,
             logCid: _logCid,
-            distributed: _distributedShares
+            distributed: _distributedShares,
+            rebate: rebateShares
         });
 
         unchecked {

src/CSFeeOracle.sol

@@ -143,6 +143,7 @@ contract CSFeeOracle is
             _treeCid: data.treeCid,
             _logCid: data.logCid,
             _distributedShares: data.distributed,
+            rebateShares: data.rebate,
             refSlot: data.refSlot
         });
     }

src/interfaces/ICSFeeDistributor.sol

@@ -21,6 +21,8 @@ interface ICSFeeDistributor is IAssetRecovererLib {
         string logCid;
         /// @notice Total amount of fees distributed in the report.
         uint256 distributed;
+        /// @notice Amount of the rebate shares in the report
+        uint256 rebate;
     }
 
     /// @dev Emitted when fees are distributed
@@ -42,10 +44,14 @@ interface ICSFeeDistributor is IAssetRecovererLib {
     /// @dev It logs how many shares were distributed in the latest report
     event ModuleFeeDistributed(uint256 shares);
 
+    /// @dev Emitted when rebate is transferred
+    event RebateTransferred(uint256 shares);
+
     error ZeroAccountingAddress();
     error ZeroStEthAddress();
     error ZeroAdminAddress();
     error ZeroOracleAddress();
+    error ZeroRebateRecipientAddress();
     error NotAccounting();
     error NotOracle();
 
@@ -65,6 +71,8 @@ interface ICSFeeDistributor is IAssetRecovererLib {
 
     function ORACLE() external view returns (address);
 
+    function REBATE_RECIPIENT() external view returns (address);
+
     function treeRoot() external view returns (bytes32);
 
     function treeCid() external view returns (string calldata);
@@ -102,12 +110,14 @@ interface ICSFeeDistributor is IAssetRecovererLib {
     /// @param _treeCid an IPFS CID of the tree
     /// @param _logCid an IPFS CID of the log
     /// @param _distributedShares an amount of the distributed shares
+    /// @param rebateShares an amount of the rebate shares
     /// @param refSlot refSlot of the report
     function processOracleReport(
         bytes32 _treeRoot,
         string calldata _treeCid,
         string calldata _logCid,
         uint256 _distributedShares,
+        uint256 rebateShares,
         uint256 refSlot
     ) external;
 

src/interfaces/ICSFeeOracle.sol

@@ -24,6 +24,8 @@ interface ICSFeeOracle is IAssetRecovererLib {
         string logCid;
         /// @notice Total amount of fees distributed in the report.
         uint256 distributed;
+        /// @notice Amount of the rebate shares in the report
+        uint256 rebate;
     }
 
     /// @dev Emitted when a new fee distributor contract is set