feat(utxo-staking): add babylon unstaking transaction functionality

Add ability to create and sign babylon unstaking transactions. Implement
test fixtures for both testnet and mock environments to validate behavior.

Issue: BTC-1966
Co-authored-by: llm-git <[email protected]>

Author: OttoAllmendinger

modules/utxo-staking/test/fixtures/babylon/unstakingTransaction.testnet.json

@@ -0,0 +1,37 @@
+{
+  "transaction": {
+    "version": 2,
+    "locktime": 0,
+    "ins": [
+      {
+        "hash": "64da14050ffd0e6186c68a59f371a0adc95cc84b0502fe0915be7eba3f771bb3",
+        "index": 0,
+        "script": "",
+        "sequence": 10000,
+        "witness": [
+          "34a9fb0ebbcd13f30cb8ca398bdedb23073c19cabb17b6de6ba4f45afea360bd9798b4fa5d2d886af2fd1e161f37787316fa3482e45ef4a6ca5692a619550ac0",
+          "207b6a08504c46336f985a5787a5423eb18c10b149fef29cd3316ad86f565cd2b9ad021027b2",
+          "c050929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac01e1d2e84c4fc6bdddf3b8018065cf5ca8405988579188585f382c51c088e882696962cb69242e00941e0a6197b7ecdb83ab8bb0490dbfd23fa4b8d26b75989eb"
+        ]
+      }
+    ],
+    "outs": [
+      {
+        "value": "54555",
+        "script": "0014896f1ba65deaeb045bb3121e20e5744e66ca0e48"
+      }
+    ],
+    "network": {
+      "messagePrefix": "\u0018Bitcoin Signed Message:\n",
+      "bech32": "bc",
+      "bip32": {
+        "public": 76067358,
+        "private": 76066276
+      },
+      "pubKeyHash": 0,
+      "scriptHash": 5,
+      "wif": 128,
+      "coin": "btc"
+    }
+  }
+}

modules/utxo-staking/test/fixtures/babylon/unstakingTransaction.testnetMock.json

@@ -0,0 +1,37 @@
+{
+  "transaction": {
+    "version": 2,
+    "locktime": 0,
+    "ins": [
+      {
+        "hash": "a999d7bc6af1a17cd4e70d0fd875a1734152dfb55f9166240f35965c79fa36c2",
+        "index": 0,
+        "script": "",
+        "sequence": 10000,
+        "witness": [
+          "3856a8f99911738be2687076e7aa977499f9db8187ed85d574e7cbaa10520252b8d954011b35d18afb875cfac5019f937a2dcbc2e4143cf12c2c120f8250a8ab",
+          "207b6a08504c46336f985a5787a5423eb18c10b149fef29cd3316ad86f565cd2b9ad021027b2",
+          "c150929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac068cc9790c0627bc8f28afd009b31974a2fce5ea4fe2ed4dd8b65c8feda196875c1d262cfe1f3b746337f6766e31854333d370f733bd845727aaed2baebc7a552"
+        ]
+      }
+    ],
+    "outs": [
+      {
+        "value": "54555",
+        "script": "0014896f1ba65deaeb045bb3121e20e5744e66ca0e48"
+      }
+    ],
+    "network": {
+      "messagePrefix": "\u0018Bitcoin Signed Message:\n",
+      "bech32": "bc",
+      "bip32": {
+        "public": 76067358,
+        "private": 76066276
+      },
+      "pubKeyHash": 0,
+      "scriptHash": 5,
+      "wif": 128,
+      "coin": "btc"
+    }
+  }
+}

modules/utxo-staking/test/unit/babylon/transactions.ts

@@ -5,7 +5,14 @@ import * as bitcoinjslib from 'bitcoinjs-lib';
 import * as utxolib from '@bitgo/utxo-lib';
 import { ECPairInterface } from '@bitgo/utxo-lib';
 import { ast, Descriptor, Miniscript } from '@bitgo/wasm-miniscript';
-import { createAddressFromDescriptor } from '@bitgo/utxo-core/descriptor';
+import {
+  createAddressFromDescriptor,
+  createPsbt,
+  getNewSignatureCount,
+  signWithKey,
+  toUtxoPsbt,
+  toWrappedPsbt,
+} from '@bitgo/utxo-core/descriptor';
 import { getFixture, toPlainObject } from '@bitgo/utxo-core/testutil';
 import { getBabylonParamByVersion } from '@bitgo/babylonlabs-io-btc-staking-ts';
 
@@ -89,6 +96,40 @@ function getStakingTransactionTreeVendor(
   };
 }
 
+function createUnstakingTransaction(
+  stakingTx: vendor.TransactionResult,
+  stakingDescriptor: Descriptor,
+  changeAddress: string,
+  { sequence }: { sequence: number }
+): utxolib.Psbt {
+  const network = utxolib.networks.bitcoin;
+  const witnessUtxoNumber = stakingTx.transaction.outs[0];
+  const witnessUtxo = {
+    script: witnessUtxoNumber.script,
+    value: BigInt(witnessUtxoNumber.value),
+  };
+  return createPsbt(
+    {
+      network,
+    },
+    [
+      {
+        hash: stakingTx.transaction.getId(),
+        index: 0,
+        witnessUtxo,
+        descriptor: stakingDescriptor,
+        sequence,
+      },
+    ],
+    [
+      {
+        script: utxolib.address.toOutputScript(changeAddress, network),
+        value: BigInt(witnessUtxoNumber.value) - 1000n,
+      },
+    ]
+  );
+}
+
 function getTestnetStakingParamsWithCovenant(
   params: vendor.StakingParams,
   covenantKeys: ECPairInterface[]
@@ -198,7 +239,7 @@ function describeWithKeys(
   stakingParams: vendor.StakingParams,
   { signIntermediateTxs = false } = {}
 ) {
-  const stakerKey = getECKey('staker');
+  const stakerKey = getECKey('staker') as ECPairInterface & { privateKey: Buffer };
   const covenantThreshold = stakingParams.covenantQuorum;
   const stakingTimelock = stakingParams.minStakingTimeBlocks;
   const unbondingTimelock = stakingParams.unbondingTime;
@@ -256,15 +297,20 @@ function describeWithKeys(
       const feeRateSatB = 2;
       const utxo = mockUtxo(mainWallet);
 
-      it('has expected transactions', async function () {
-        const stakingTx = vendor.stakingTransaction(
+      let stakingTx: vendor.TransactionResult;
+
+      before('setup stakingTx', function () {
+        stakingTx = vendor.stakingTransaction(
           vendorBuilder.buildScripts(),
           amount,
           changeAddress,
           [mockUtxo(mainWallet)],
           bitcoinjslib.networks.bitcoin,
           feeRateSatB
         );
+      });
+
+      it('has expected transactions', async function () {
         await assertTransactionEqualsFixture(`test/fixtures/babylon/stakingTransaction.${tag}.json`, stakingTx);
 
         // simply one staking output and one change output
@@ -337,6 +383,22 @@ function describeWithKeys(
           );
         }
       });
+
+      it('creates unstaking transaction', async function () {
+        const unstaking = createUnstakingTransaction(
+          stakingTx,
+          descriptorBuilder.getStakingDescriptor(),
+          changeAddress,
+          { sequence: stakingParams.minStakingTimeBlocks }
+        );
+        const wrappedPsbt = toWrappedPsbt(unstaking);
+        assert(getNewSignatureCount(signWithKey(wrappedPsbt, stakerKey)) > 0);
+        wrappedPsbt.finalize();
+        const tx = toUtxoPsbt(wrappedPsbt, utxolib.networks.bitcoin).extractTransaction();
+        await assertTransactionEqualsFixture(`test/fixtures/babylon/unstakingTransaction.${tag}.json`, {
+          transaction: tx,
+        });
+      });
     });
   });
 }