fix(sdk-coin-eth): guard BN construction in signFinal for EIP-1559 txns

In Eth.signFinal (the second-signature path for WRW/offline-vault
transactions), the ethTxParams object was unconditionally calling
`new BN(txPrebuild.gasPrice)`. For EIP-1559 transactions, gasPrice
is absent from txPrebuild, so bn.js received undefined and threw
"Cannot read properties of undefined (reading 'toString')" internally.

The buildTransaction helper already handles EIP-1559 correctly by
consuming maxFeePerGas/maxPriorityFeePerGas from the eip1559 field and
ignoring gasPrice when eip1559 is present, so passing undefined is safe.

The fix skips BN construction when txPrebuild.eip1559 is set, preventing
the crash when users raise fees on EIP-1559 Ethereum transactions.

Added a WRWUnsignedSweepEIP1559ETHTx fixture and a corresponding test
that exercises the isLastSignature=true path with an EIP-1559 txPrebuild
(no gasPrice field).

Ticket: COINS-572
Session-Id: afc68d99-c916-424d-bffc-d814dea1d611
Task-Id: 60985a53-c0de-4df0-9fb9-187bad6e4464

Author: Support Bot

modules/sdk-coin-eth/src/eth.ts

@@ -429,7 +429,7 @@ export class Eth extends AbstractEthLikeNewCoins {
       nonce:
         params.signingKeyNonce !== undefined ? params.signingKeyNonce : params.txPrebuild.halfSigned?.backupKeyNonce,
       value: 0,
-      gasPrice: new optionalDeps.ethUtil.BN(txPrebuild.gasPrice),
+      gasPrice: txPrebuild.eip1559 ? undefined : new optionalDeps.ethUtil.BN(txPrebuild.gasPrice),
       gasLimit: new optionalDeps.ethUtil.BN(txPrebuild.gasLimit),
       data: sendData,
     };

modules/sdk-coin-eth/test/fixtures/eth.ts

@@ -151,6 +151,33 @@ module.exports.WRWUnsignedSweepETHTx = {
   nextContractSequenceId: 1,
 };
 
+module.exports.WRWUnsignedSweepEIP1559ETHTx = {
+  tx: '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',
+  userKey:
+    'xpub661MyMwAqRbcFcNDKt46HgPAJTfNyQUS6M7i8jUwZKHz9wZGaK1XdQuT8XU5PkFfbrfoGXc1C4QD9PDJ7zhpu52rLzzynovwgcXh7NtDbH9',
+  backupKey:
+    'xpub661MyMwAqRbcGUJYcAgycBqG5HrQoUJAvBv7PEbvjGGffdtMP8hx3DX9AwzaY4vA7ynqHfxzRTRLwS2E9DH1HRPG8u7kWXd4JMCNgonGGnk',
+  coin: 'teth',
+  eip1559: { maxFeePerGas: '40000000000', maxPriorityFeePerGas: '2000000000' },
+  gasLimit: '500000',
+  recipients: [
+    {
+      address: '0xa98fdfc2c711260cd665a3884b509b4a5ad6f4e8',
+      amount: '4000000000000000000',
+    },
+  ],
+  walletContractAddress: '0xfd12f1d563650fbdd9314dce06992159778f6343',
+  amount: '4000000000000000000',
+  backupKeyNonce: 0,
+  recipient: {
+    address: '0xa98fdfc2c711260cd665a3884b509b4a5ad6f4e8',
+    amount: '4000000000000000000',
+  },
+  expireTime: 1600800540,
+  contractSequenceId: 1,
+  nextContractSequenceId: 1,
+};
+
 module.exports.WRWUnsignedSweepERC20Tx = {
   tx: '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',
   userKey:

modules/sdk-coin-eth/test/unit/ethWallet.ts

@@ -485,4 +485,30 @@ describe('final-sign transaction from WRW', function () {
     outputs[0].address.should.equal(fixtures.WRWUnsignedSweepERC20Tx.recipient.address);
     outputs[0].amount.should.equal(fixtures.WRWUnsignedSweepERC20Tx.recipient.amount);
   });
+
+  it('should add a second EIP-1559 signature to unsigned sweep for teth without throwing when gasPrice is absent', async function () {
+    const bitgo = TestBitGo.decorate(BitGoAPI, { env: 'test' });
+    bitgo.safeRegister('teth', Teth.createInstance);
+    const basecoin: any = bitgo.coin('teth');
+    const gasLimit = 500000;
+    const prv =
+      'xprv9s21ZrQH143K3D8TXfvAJgHVfTEeQNW5Ys9wZtnUZkqPzFzSjbEJrWC1vZ4GnXCvR7rQL2UFX3RSuYeU9MrERm1XBvACow7c36vnz5iYyj2';
+    const tx = {
+      txPrebuild: fixtures.WRWUnsignedSweepEIP1559ETHTx,
+      prv,
+    };
+    const halfSigned = await basecoin.signTransaction(tx);
+
+    const wrapper = {} as SignTransactionOptions;
+    wrapper.txPrebuild = halfSigned;
+    wrapper.txPrebuild.recipients = halfSigned.halfSigned.recipients;
+    wrapper.txPrebuild.eip1559 = fixtures.WRWUnsignedSweepEIP1559ETHTx.eip1559;
+    wrapper.txPrebuild.gasLimit = gasLimit.toString();
+    wrapper.isLastSignature = true;
+    wrapper.walletContractAddress = fixtures.WRWUnsignedSweepEIP1559ETHTx.walletContractAddress;
+    wrapper.prv = prv;
+
+    const finalSignedTx = await basecoin.signTransaction(wrapper);
+    finalSignedTx.should.have.property('txHex');
+  });
 });