Add DODO-only EnhancedSwapRouterV2 routing helpers

contracts/liquidity/providers/FixedRateLiquidityProvider.sol

@@ -0,0 +1,122 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.20;
+
+import "@openzeppelin/contracts/access/AccessControl.sol";
+import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
+import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
+import "../interfaces/ILiquidityProvider.sol";
+
+/**
+ * @title FixedRateLiquidityProvider
+ * @notice Narrow Chain 138 prep provider for token pairs that need executable
+ *         router-backed conversion while a DODO pool direction is unhealthy.
+ */
+contract FixedRateLiquidityProvider is ILiquidityProvider, AccessControl {
+    using SafeERC20 for IERC20;
+
+    bytes32 public constant RATE_MANAGER_ROLE = keccak256("RATE_MANAGER_ROLE");
+
+    address public immutable tokenIn;
+    address public immutable tokenOut;
+
+    uint256 public amountOutPerTokenIn;
+    uint256 public slippageBps;
+    uint256 public gasEstimate;
+    bool public enabled = true;
+
+    event RateUpdated(uint256 amountOutPerTokenIn, uint256 slippageBps);
+    event EnabledSet(bool enabled);
+    event SwapExecuted(address indexed caller, uint256 amountIn, uint256 amountOut);
+    event Swept(address indexed token, address indexed recipient, uint256 amount);
+
+    constructor(
+        address admin,
+        address tokenIn_,
+        address tokenOut_,
+        uint256 amountOutPerTokenIn_,
+        uint256 slippageBps_,
+        uint256 gasEstimate_
+    ) {
+        require(admin != address(0), "FixedRateLiquidityProvider: zero admin");
+        require(tokenIn_ != address(0), "FixedRateLiquidityProvider: zero tokenIn");
+        require(tokenOut_ != address(0), "FixedRateLiquidityProvider: zero tokenOut");
+        require(tokenIn_ != tokenOut_, "FixedRateLiquidityProvider: same token");
+        require(amountOutPerTokenIn_ > 0, "FixedRateLiquidityProvider: zero rate");
+
+        tokenIn = tokenIn_;
+        tokenOut = tokenOut_;
+        amountOutPerTokenIn = amountOutPerTokenIn_;
+        slippageBps = slippageBps_;
+        gasEstimate = gasEstimate_;
+
+        _grantRole(DEFAULT_ADMIN_ROLE, admin);
+        _grantRole(RATE_MANAGER_ROLE, admin);
+    }
+
+    function setRate(uint256 amountOutPerTokenIn_, uint256 slippageBps_) external onlyRole(RATE_MANAGER_ROLE) {
+        require(amountOutPerTokenIn_ > 0, "FixedRateLiquidityProvider: zero rate");
+        amountOutPerTokenIn = amountOutPerTokenIn_;
+        slippageBps = slippageBps_;
+        emit RateUpdated(amountOutPerTokenIn_, slippageBps_);
+    }
+
+    function setEnabled(bool enabled_) external onlyRole(RATE_MANAGER_ROLE) {
+        enabled = enabled_;
+        emit EnabledSet(enabled_);
+    }
+
+    function setGasEstimate(uint256 gasEstimate_) external onlyRole(RATE_MANAGER_ROLE) {
+        gasEstimate = gasEstimate_;
+    }
+
+    function getQuote(
+        address tokenIn_,
+        address tokenOut_,
+        uint256 amountIn
+    ) external view override returns (uint256 amountOut, uint256 quoteSlippageBps) {
+        if (!enabled || tokenIn_ != tokenIn || tokenOut_ != tokenOut || amountIn == 0) {
+            return (0, 10_000);
+        }
+
+        amountOut = (amountIn * amountOutPerTokenIn) / 1e18;
+        quoteSlippageBps = slippageBps;
+    }
+
+    function executeSwap(
+        address tokenIn_,
+        address tokenOut_,
+        uint256 amountIn,
+        uint256 minAmountOut
+    ) external override returns (uint256 amountOut) {
+        require(enabled, "FixedRateLiquidityProvider: disabled");
+        require(tokenIn_ == tokenIn && tokenOut_ == tokenOut, "FixedRateLiquidityProvider: unsupported pair");
+        require(amountIn > 0, "FixedRateLiquidityProvider: zero amount");
+
+        amountOut = (amountIn * amountOutPerTokenIn) / 1e18;
+        require(amountOut >= minAmountOut, "FixedRateLiquidityProvider: insufficient output");
+        require(IERC20(tokenOut).balanceOf(address(this)) >= amountOut, "FixedRateLiquidityProvider: insufficient liquidity");
+
+        IERC20(tokenIn).safeTransferFrom(msg.sender, address(this), amountIn);
+        IERC20(tokenOut).safeTransfer(msg.sender, amountOut);
+
+        emit SwapExecuted(msg.sender, amountIn, amountOut);
+    }
+
+    function supportsTokenPair(address tokenIn_, address tokenOut_) external view override returns (bool) {
+        return enabled && tokenIn_ == tokenIn && tokenOut_ == tokenOut;
+    }
+
+    function providerName() external pure override returns (string memory) {
+        return "Fixed Rate Liquidity Provider";
+    }
+
+    function estimateGas(address, address, uint256) external view override returns (uint256) {
+        return gasEstimate;
+    }
+
+    function sweep(address token, address recipient, uint256 amount) external onlyRole(DEFAULT_ADMIN_ROLE) {
+        require(recipient != address(0), "FixedRateLiquidityProvider: zero recipient");
+        IERC20(token).safeTransfer(recipient, amount);
+        emit Swept(token, recipient, amount);
+    }
+}