fix: move req.json() inside try/catch to handle invalid JSON body

[memosr]

Problem

In app/api/gateway/transfer/route.ts, the req.json() destructuring happens before the try block starts at line 46:

const { sourceChain, destinationChain, amount, recipientAddress } =
  await req.json();

try {
  // ...
}

This means:

• Invalid JSON in the request body throws an uncaught SyntaxError, producing an unhandled 500 instead of a proper 400
• The variables are referenced in the catch block (lines 241-244 for the failed-transaction logger) where they may be undefined

Fix

- const { sourceChain, destinationChain, amount, recipientAddress } =
-   await req.json();
+ let sourceChain: string | undefined;
+ let destinationChain: string | undefined;
+ let amount: string | undefined;
+ let recipientAddress: string | undefined;
 
  try {
+   ({ sourceChain, destinationChain, amount, recipientAddress } =
+     await req.json());

And at the top of catch:

if (error instanceof SyntaxError) {
  return NextResponse.json({ error: "Invalid JSON body" }, { status: 400 });
}

The SyntaxError check is intentionally first — before console.error and the INSUFFICIENT_GAS check — so malformed-body errors never get logged as unexpected transfer failures.

Impact

• Correctness: Malformed JSON returns proper 400 instead of unhandled 500
• Risk: Low — variables remain accessible in catch block via outer scope
• Other routes checked: balance/route.ts and deposit/route.ts already call req.json() inside their try blocks, no changes needed