feat(wasm-utxo): add method to get unsigned txid from psbt

Added `unsignedTxid` method to BitGoPsbt class, which returns the
transaction ID of the unsigned transaction contained in the PSBT.
Added tests to verify the method works correctly.

Issue: BTC-2652

Co-authored-by: llm-git <llm-git@ttll.de>

Author: OttoAllmendinger

packages/wasm-utxo/js/fixedScriptWallet.ts

@@ -94,6 +94,14 @@ export class BitGoPsbt {
     return new BitGoPsbt(wasm);
   }
 
+  /**
+   * Get the unsigned transaction ID
+   * @returns The unsigned transaction ID
+   */
+  unsignedTxid(): string {
+    return this.wasm.unsigned_txid();
+  }
+
   /**
    * Parse transaction with wallet keys to identify wallet inputs/outputs
    * @param walletKeys - The wallet keys to use for identification

packages/wasm-utxo/src/fixed_script_wallet/bitgo_psbt/mod.rs

@@ -13,7 +13,7 @@ mod sighash;
 mod zcash_psbt;
 
 use crate::Network;
-use miniscript::bitcoin::{psbt::Psbt, secp256k1, CompressedPublicKey};
+use miniscript::bitcoin::{psbt::Psbt, secp256k1, CompressedPublicKey, Txid};
 pub use propkv::{BitGoKeyValue, ProprietaryKeySubtype, BITGO};
 pub use sighash::validate_sighash_type;
 use zcash_psbt::ZcashPsbt;
@@ -319,6 +319,11 @@ impl BitGoPsbt {
         }
     }
 
+    /// Get the unsigned transaction ID
+    pub fn unsigned_txid(&self) -> Txid {
+        self.psbt().unsigned_tx.compute_txid()
+    }
+
     /// Helper function to create a MuSig2 context for an input
     ///
     /// This validates that:

packages/wasm-utxo/src/wasm/fixed_script_wallet.rs

@@ -147,6 +147,11 @@ impl BitGoPsbt {
         Ok(BitGoPsbt { psbt })
     }
 
+    /// Get the unsigned transaction ID
+    pub fn unsigned_txid(&self) -> String {
+        self.psbt.unsigned_txid().to_string()
+    }
+
     /// Parse transaction with wallet keys to identify wallet inputs/outputs
     pub fn parse_transaction_with_wallet_keys(
         &self,

packages/wasm-utxo/test/fixedScript/parseTransactionWithWalletKeys.ts

@@ -88,6 +88,15 @@ describe("parseTransactionWithWalletKeys", function () {
         rootWalletKeys = loadWalletKeysFromFixture(networkName);
       });
 
+      it("should have matching unsigned transaction ID", function () {
+        const unsignedTxid = bitgoPsbt.unsignedTxid();
+        const expectedUnsignedTxid = utxolib.bitgo
+          .createPsbtFromBuffer(psbtBytes, network)
+          .getUnsignedTx()
+          .getId();
+        assert.strictEqual(unsignedTxid, expectedUnsignedTxid);
+      });
+
       it("should parse transaction and identify internal/external outputs", function () {
         const parsed = bitgoPsbt.parseTransactionWithWalletKeys(rootWalletKeys, {
           outputScripts: [replayProtectionScript],