feat: extend Mantle layer 1 gas fee flow to support Mantle Sepolia testnet

Add Mantle Sepolia (chain ID 0x138b) to MantleLayer1GasFeeFlow so the
tokenRatio conversion applies to testnet transactions as well.

Author: jeremy-consensys

packages/transaction-controller/CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 - Add Mantle layer 1 gas fee flow with tokenRatio conversion for accurate MNT-denominated gas estimates ([#8376](https://github.com/MetaMask/core/pull/8376))
+- Extend Mantle layer 1 gas fee flow to support Mantle Sepolia testnet (chain ID `0x138b`)
 
 ### Changed
 

packages/transaction-controller/src/constants.ts

@@ -34,6 +34,7 @@ export const CHAIN_IDS = {
   MEGAETH_TESTNET: '0x18c6',
   SEI: '0x531',
   MANTLE: '0x1388',
+  MANTLE_SEPOLIA: '0x138b',
 } as const;
 
 /** Extract of the Wrapped ERC-20 ABI required for simulation. */

packages/transaction-controller/src/gas-flows/MantleLayer1GasFeeFlow.test.ts

@@ -33,6 +33,15 @@ const TRANSACTION_META_MOCK: TransactionMeta = {
   txParams: TRANSACTION_PARAMS_MOCK,
 };
 
+const TRANSACTION_META_TESTNET_MOCK: TransactionMeta = {
+  id: '2',
+  chainId: CHAIN_IDS.MANTLE_SEPOLIA,
+  networkClientId: 'testNetworkClientId',
+  status: TransactionStatus.unapproved,
+  time: 0,
+  txParams: TRANSACTION_PARAMS_MOCK,
+};
+
 const SERIALIZED_TRANSACTION_MOCK = '0x1234';
 // L1 fee in ETH (returned by oracle)
 const L1_FEE_MOCK = '0x0de0b6b3a7640000'; // 1e18 (1 ETH in wei)
@@ -104,6 +113,17 @@ describe('MantleLayer1GasFeeFlow', () => {
       ).toBe(true);
     });
 
+    it('returns true if chain ID is Mantle Sepolia', async () => {
+      const flow = new MantleLayer1GasFeeFlow();
+
+      expect(
+        await flow.matchesTransaction({
+          transactionMeta: TRANSACTION_META_TESTNET_MOCK,
+          messenger,
+        }),
+      ).toBe(true);
+    });
+
     it('returns false if chain ID is not Mantle', async () => {
       const flow = new MantleLayer1GasFeeFlow();
 
@@ -243,7 +263,7 @@ describe('MantleLayer1GasFeeFlow', () => {
       );
     });
 
-    it('uses default OP Stack oracle address', () => {
+    it('uses default OP Stack oracle address for mainnet', () => {
       class TestableMantleLayer1GasFeeFlow extends MantleLayer1GasFeeFlow {
         exposeOracleAddress(chainId: Hex): Hex {
           return super.getOracleAddressForChain(chainId);
@@ -255,5 +275,55 @@ describe('MantleLayer1GasFeeFlow', () => {
         '0x420000000000000000000000000000000000000F',
       );
     });
+
+    it('uses default OP Stack oracle address for Mantle Sepolia', () => {
+      class TestableMantleLayer1GasFeeFlow extends MantleLayer1GasFeeFlow {
+        exposeOracleAddress(chainId: Hex): Hex {
+          return super.getOracleAddressForChain(chainId);
+        }
+      }
+
+      const flow = new TestableMantleLayer1GasFeeFlow();
+      expect(flow.exposeOracleAddress(CHAIN_IDS.MANTLE_SEPOLIA)).toBe(
+        '0x420000000000000000000000000000000000000F',
+      );
+    });
+
+    it('computes correct fee for Mantle Sepolia transactions', async () => {
+      const gasUsed = '0x5208';
+      request = {
+        ...request,
+        transactionMeta: {
+          ...TRANSACTION_META_TESTNET_MOCK,
+          gasUsed,
+        },
+      };
+
+      contractGetOperatorFeeMock.mockResolvedValueOnce(
+        bnFromHex(OPERATOR_FEE_MOCK),
+      );
+
+      jest
+        .spyOn(TransactionFactory, 'fromTxData')
+        .mockReturnValueOnce(
+          createMockTypedTransaction(
+            Buffer.from(SERIALIZED_TRANSACTION_MOCK, 'hex'),
+          ),
+        );
+
+      const flow = new MantleLayer1GasFeeFlow();
+      const response = await flow.getLayer1Fee(request);
+
+      const expectedL1FeeInMnt = bnFromHex(L1_FEE_MOCK).mul(TOKEN_RATIO_MOCK);
+      const expectedTotal = expectedL1FeeInMnt.add(
+        bnFromHex(OPERATOR_FEE_MOCK),
+      );
+
+      expect(contractTokenRatioMock).toHaveBeenCalledTimes(1);
+      expect(contractGetOperatorFeeMock).toHaveBeenCalledTimes(1);
+      expect(response).toStrictEqual({
+        layer1Fee: add0x(padHexToEvenLength(expectedTotal.toString(16))),
+      });
+    });
   });
 });

packages/transaction-controller/src/gas-flows/MantleLayer1GasFeeFlow.ts

@@ -19,7 +19,7 @@ import { padHexToEvenLength, toBN } from '../utils/utils';
 
 const log = createModuleLogger(projectLogger, 'mantle-layer1-gas-fee-flow');
 
-const MANTLE_CHAIN_IDS: Hex[] = [CHAIN_IDS.MANTLE];
+const MANTLE_CHAIN_IDS: Hex[] = [CHAIN_IDS.MANTLE, CHAIN_IDS.MANTLE_SEPOLIA];
 
 const ZERO = new BN(0);