Implement EVM L2 cross-chain fee rebates

solidity/contracts/bridge/Bridge.sol

@@ -26,6 +26,7 @@ import "./IRelay.sol";
 import "./BridgeState.sol";
 import "./Deposit.sol";
 import "./DepositSweep.sol";
+import "./RebateStaking.sol";
 import "./Redemption.sol";
 import "./BitcoinTx.sol";
 import "./EcdsaLib.sol";
@@ -243,6 +244,12 @@ contract Bridge is
         address oldRebateStaking,
         address newRebateStaking
     );
+    event CrossChainIntegratorUpdated(
+        address indexed integrator,
+        bool authorized,
+        uint256 evmSourceChainId,
+        uint16 wormholeChainId
+    );
 
     /// @notice Emitted when a deposit's vault field is corrected via governance.
     /// @dev This event is used for transparency when fixing deposits that were
@@ -477,6 +484,24 @@ contract Bridge is
         self.revealDepositWithExtraData(fundingTx, reveal, extraData);
     }
 
+    /// @notice Reveals a P2(W)SH Bitcoin deposit with extra data and applies
+    ///         treasury fee rebate to a separate L1 beneficiary.
+    function revealDepositWithExtraDataAndRebate(
+        BitcoinTx.Info calldata fundingTx,
+        Deposit.DepositRevealInfo calldata reveal,
+        bytes32 extraData,
+        address rebateBeneficiary,
+        RebateStaking.BeneficiaryRebateContext calldata rebateContext
+    ) external {
+        self.revealDepositWithExtraDataAndRebate(
+            fundingTx,
+            reveal,
+            extraData,
+            rebateBeneficiary,
+            rebateContext
+        );
+    }
+
     /// @notice Used by the wallet to prove the BTC deposit sweep transaction
     ///         and to update Bank balances accordingly. Sweep is only accepted
     ///         if it satisfies SPV proof.
@@ -580,6 +605,31 @@ contract Bridge is
         );
     }
 
+    /// @notice Requests redemption with a separate refund recipient and rebate
+    ///         beneficiary. Only governance-authorized cross-chain integrators
+    ///         may use this entry point.
+    function requestRedemptionWithRebate(
+        bytes20 walletPubKeyHash,
+        BitcoinTx.UTXO calldata mainUtxo,
+        address balanceOwner,
+        address refundRecipient,
+        bytes calldata redeemerOutputScript,
+        uint64 amount,
+        address rebateBeneficiary,
+        RebateStaking.BeneficiaryRebateContext calldata rebateContext
+    ) external {
+        self.requestRedemptionWithRebate(
+            walletPubKeyHash,
+            mainUtxo,
+            balanceOwner,
+            refundRecipient,
+            redeemerOutputScript,
+            amount,
+            rebateBeneficiary,
+            rebateContext
+        );
+    }
+
     /// @notice Requests redemption of the given amount from the specified
     ///         wallet to the redeemer Bitcoin output script. Used by
     ///         `Bank.approveBalanceAndCall`. Can handle more complex cases
@@ -2037,6 +2087,40 @@ contract Bridge is
         return self.rebateStaking;
     }
 
+    /// @notice Updates authorization for an L1 cross-chain integrator.
+    function setCrossChainIntegrator(
+        address integrator,
+        bool authorized,
+        uint256 evmSourceChainId,
+        uint16 wormholeChainId
+    ) external onlyGovernance {
+        self.setCrossChainIntegrator(
+            integrator,
+            authorized,
+            evmSourceChainId,
+            wormholeChainId
+        );
+    }
+
+    /// @notice Returns cross-chain integrator configuration.
+    function crossChainIntegrator(address integrator)
+        external
+        view
+        returns (
+            bool authorized,
+            uint256 evmSourceChainId,
+            uint16 wormholeChainId
+        )
+    {
+        BridgeState.CrossChainIntegrator storage entry = self
+            .crossChainIntegrators[integrator];
+        return (
+            entry.authorized,
+            entry.evmSourceChainId,
+            entry.wormholeChainId
+        );
+    }
+
     /// @notice Sets the redemption watchtower address.
     /// @param redemptionWatchtower Address of the redemption watchtower.
     /// @dev Requirements:

solidity/contracts/bridge/BridgeGovernance.sol

@@ -1807,4 +1807,23 @@ contract BridgeGovernance is Ownable {
     function setRebateStaking(address rebateStaking) external onlyOwner {
         bridge.setRebateStaking(rebateStaking);
     }
+
+    /// @notice Updates authorization for an L1 cross-chain integrator.
+    /// @param integrator L1 depositor or redeemer contract.
+    /// @param authorized Whether beneficiary-aware Bridge entry points are allowed.
+    /// @param evmSourceChainId EVM chain ID of the L2 origin chain.
+    /// @param wormholeChainId Optional Wormhole chain ID of the L2 origin chain.
+    function setCrossChainIntegrator(
+        address integrator,
+        bool authorized,
+        uint256 evmSourceChainId,
+        uint16 wormholeChainId
+    ) external onlyOwner {
+        bridge.setCrossChainIntegrator(
+            integrator,
+            authorized,
+            evmSourceChainId,
+            wormholeChainId
+        );
+    }
 }

solidity/contracts/bridge/BridgeState.sol

@@ -28,6 +28,17 @@ import "./MovingFunds.sol";
 import "../bank/Bank.sol";
 
 library BridgeState {
+    struct CrossChainIntegrator {
+        bool authorized;
+        uint256 evmSourceChainId;
+        uint16 wormholeChainId;
+    }
+
+    struct CrossChainRedemptionRebate {
+        address rebateBeneficiary;
+        bytes32 actionId;
+    }
+
     struct Storage {
         // Address of the Bank the Bridge belongs to.
         Bank bank;
@@ -325,14 +336,20 @@ library BridgeState {
         // governance wiring; changing it afterwards requires a dedicated
         // upgrade path of the Bridge implementation.
         address rebateStaking;
+        // L1 contracts authorized to pass cross-chain rebate context into the
+        // Bridge. Each entry binds the integrator to an EVM source chain ID.
+        mapping(address => CrossChainIntegrator) crossChainIntegrators;
+        // Cross-chain redemption rebate metadata keyed by redemption key. Used
+        // to cancel rebate capacity by action ID if the redemption times out.
+        mapping(uint256 => CrossChainRedemptionRebate) crossChainRedemptionRebates;
         // Reserved storage space in case we need to add more variables.
         // The convention from OpenZeppelin suggests the storage space should
         // add up to 50 slots. Here we want to have more slots as there are
         // planned upgrades of the Bridge contract. If more entires are added to
         // the struct in the upcoming versions we need to reduce the array size.
         // See https://docs.openzeppelin.com/contracts/4.x/upgradeable#storage_gaps
         // slither-disable-next-line unused-state
-        uint256[48] __gap;
+        uint256[46] __gap;
     }
 
     event DepositParametersUpdated(
@@ -393,6 +410,13 @@ library BridgeState {
     // parameter events.
     event RebateStakingSet(address rebateStaking);
 
+    event CrossChainIntegratorUpdated(
+        address indexed integrator,
+        bool authorized,
+        uint256 evmSourceChainId,
+        uint16 wormholeChainId
+    );
+
     /// @notice Updates parameters of deposits.
     /// @param _depositDustThreshold New value of the deposit dust threshold in
     ///        satoshis. It is the minimal amount that can be requested to
@@ -892,4 +916,36 @@ library BridgeState {
         self.rebateStaking = _rebateStaking;
         emit RebateStakingSet(_rebateStaking);
     }
+
+    /// @notice Updates authorization for an L1 cross-chain integrator.
+    /// @param integrator L1 depositor or redeemer contract.
+    /// @param authorized Whether the integrator may use beneficiary-aware paths.
+    /// @param evmSourceChainId EVM chain ID of the L2 origin chain.
+    /// @param wormholeChainId Optional Wormhole chain ID for the origin chain.
+    function setCrossChainIntegrator(
+        Storage storage self,
+        address integrator,
+        bool authorized,
+        uint256 evmSourceChainId,
+        uint16 wormholeChainId
+    ) internal {
+        require(integrator != address(0), "Integrator must not be 0x0");
+        require(
+            !authorized || evmSourceChainId != 0,
+            "Source chain ID must not be 0"
+        );
+
+        self.crossChainIntegrators[integrator] = CrossChainIntegrator(
+            authorized,
+            evmSourceChainId,
+            wormholeChainId
+        );
+
+        emit CrossChainIntegratorUpdated(
+            integrator,
+            authorized,
+            evmSourceChainId,
+            wormholeChainId
+        );
+    }
 }

solidity/contracts/bridge/Deposit.sol

@@ -174,7 +174,24 @@ library Deposit {
         BitcoinTx.Info calldata fundingTx,
         DepositRevealInfo calldata reveal
     ) external {
-        _revealDeposit(self, fundingTx, reveal, bytes32(0));
+        RebateStaking.BeneficiaryRebateContext
+            memory emptyContext = RebateStaking.BeneficiaryRebateContext({
+                sourceChainId: 0,
+                l2User: address(0),
+                flowType: RebateStaking.RebateFlowType.Deposit,
+                actionId: bytes32(0),
+                maxRebateSat: 0,
+                authorization: new bytes(0)
+            });
+        _revealDeposit(
+            self,
+            fundingTx,
+            reveal,
+            bytes32(0),
+            address(0),
+            emptyContext,
+            false
+        );
     }
 
     /// @notice Internal function encapsulating the core logic of the deposit
@@ -194,7 +211,10 @@ library Deposit {
         BridgeState.Storage storage self,
         BitcoinTx.Info calldata fundingTx,
         DepositRevealInfo calldata reveal,
-        bytes32 extraData
+        bytes32 extraData,
+        address rebateBeneficiary,
+        RebateStaking.BeneficiaryRebateContext memory rebateContext,
+        bool useCrossChainRebate
     ) internal {
         require(
             self.registeredWallets[reveal.walletPubKeyHash].state ==
@@ -317,15 +337,21 @@ library Deposit {
             )
             .hash256View();
 
-        DepositRequest storage deposit = self.deposits[
-            uint256(
-                keccak256(
-                    abi.encodePacked(fundingTxHash, reveal.fundingOutputIndex)
-                )
+        uint256 depositKey = uint256(
+            keccak256(
+                abi.encodePacked(fundingTxHash, reveal.fundingOutputIndex)
             )
-        ];
+        );
+        DepositRequest storage deposit = self.deposits[depositKey];
         require(deposit.revealedAt == 0, "Deposit already revealed");
 
+        if (useCrossChainRebate) {
+            require(
+                rebateContext.actionId == bytes32(depositKey),
+                "Wrong deposit rebate action ID"
+            );
+        }
+
         uint64 fundingOutputAmount = fundingOutput.extractValue();
 
         require(
@@ -344,12 +370,22 @@ library Deposit {
         deposit.extraData = extraData;
 
         if (deposit.treasuryFee > 0 && self.rebateStaking != address(0)) {
-            deposit.treasuryFee = RebateStaking(self.rebateStaking)
-                .applyForRebate(
-                    deposit.depositor,
-                    deposit.treasuryFee,
-                    RebateStaking.TreasuryFeeType.Deposit
-                );
+            if (useCrossChainRebate) {
+                deposit.treasuryFee = RebateStaking(self.rebateStaking)
+                    .applyForRebateFor(
+                        rebateBeneficiary,
+                        deposit.treasuryFee,
+                        RebateStaking.TreasuryFeeType.Deposit,
+                        rebateContext
+                    );
+            } else {
+                deposit.treasuryFee = RebateStaking(self.rebateStaking)
+                    .applyForRebate(
+                        deposit.depositor,
+                        deposit.treasuryFee,
+                        RebateStaking.TreasuryFeeType.Deposit
+                    );
+            }
         }
 
         _emitDepositRevealedEvent(fundingTxHash, fundingOutputAmount, reveal);
@@ -410,7 +446,55 @@ library Deposit {
         // reveal flow and reduce potential attack surface.
         require(extraData != bytes32(0), "Extra data must not be empty");
 
-        _revealDeposit(self, fundingTx, reveal, extraData);
+        RebateStaking.BeneficiaryRebateContext
+            memory emptyContext = RebateStaking.BeneficiaryRebateContext({
+                sourceChainId: 0,
+                l2User: address(0),
+                flowType: RebateStaking.RebateFlowType.Deposit,
+                actionId: bytes32(0),
+                maxRebateSat: 0,
+                authorization: new bytes(0)
+            });
+        _revealDeposit(
+            self,
+            fundingTx,
+            reveal,
+            extraData,
+            address(0),
+            emptyContext,
+            false
+        );
+    }
+
+    /// @notice Reveals a P2(W)SH Bitcoin deposit with extra data and applies
+    ///         deposit treasury fee rebate to a separate L1 beneficiary.
+    function revealDepositWithExtraDataAndRebate(
+        BridgeState.Storage storage self,
+        BitcoinTx.Info calldata fundingTx,
+        DepositRevealInfo calldata reveal,
+        bytes32 extraData,
+        address rebateBeneficiary,
+        RebateStaking.BeneficiaryRebateContext calldata rebateContext
+    ) external {
+        require(extraData != bytes32(0), "Extra data must not be empty");
+
+        BridgeState.CrossChainIntegrator storage integrator = self
+            .crossChainIntegrators[msg.sender];
+        require(integrator.authorized, "Caller is not cross-chain integrator");
+        require(
+            rebateContext.sourceChainId == integrator.evmSourceChainId,
+            "Wrong rebate source chain"
+        );
+
+        _revealDeposit(
+            self,
+            fundingTx,
+            reveal,
+            extraData,
+            rebateBeneficiary,
+            rebateContext,
+            true
+        );
     }
 
     /// @notice Validates the deposit refund locktime. The validation passes