fix: Resolve TypeScript build errors in backend

- Fix cancel.ts: handle string | string[] for streamId parameter
- Fix sorobanService.ts: add Transaction import
- Fix sorobanService.ts: call build() on assembled transaction before signing

Author: jotel-dev

backend/src/controllers/stream/cancel.ts

@@ -54,7 +54,11 @@ export const cancelStreamHandler = async (req: AuthenticatedRequest, res: Respon
       return res.status(400).json({ error: 'Missing streamId parameter' });
     }
 
-    const parsedStreamId = parseInt(streamId, 10);
+    const streamIdStr = Array.isArray(streamId) ? streamId[0] : streamId;
+    if (!streamIdStr) {
+      return res.status(400).json({ error: 'Invalid streamId parameter' });
+    }
+    const parsedStreamId = parseInt(streamIdStr, 10);
 
     // 1. Fetch stream from DB
     const stream = await prisma.stream.findUnique({

backend/src/services/sorobanService.ts

@@ -1,4 +1,4 @@
-import { rpc, xdr, StrKey, Contract, nativeToScVal, Keypair, TransactionBuilder, Account, Networks } from '@stellar/stellar-sdk';
+import { rpc, xdr, StrKey, Contract, nativeToScVal, Keypair, TransactionBuilder, Account, Networks, Transaction } from '@stellar/stellar-sdk';
 import logger from '../logger.js';
 
 const RPC_URL = process.env.SOROBAN_RPC_URL ?? 'https://soroban-testnet.stellar.org';
@@ -104,7 +104,7 @@ async function submitContractCall(method: string, args: xdr.ScVal[], senderSecre
   }
 
   // Assemble transaction with simulation results
-  const assembledTx = rpc.assembleTransaction(tx, simulation);
+  const assembledTx = rpc.assembleTransaction(tx, simulation).build();
   assembledTx.sign(keypair);
 
   const response = await server.sendTransaction(assembledTx);