Nextjs tRPC POST Requests Hang with Cloudflare DNS Proxy Enabled

Question

ProjectID: 7d98cee2-4752-43e0-9546-7593b2de0068
### Environment Details
- **Project Type:** Next.js application with tRPC
- **tRPC Version:** v11
- **Cloudflare Configuration:** Full protection with DNS proxy enabled

### Problem Description
When using Cloudflare with DNS proxy enabled (orange cloud), tRPC mutation requests (POST) hang indefinitely, while query requests (GET) continue to work successfully. It is fine with local and my vps server but fail in railway.

### Technical Details
- **Working:** All tRPC query operations that use GET requests
- **Not Working:** All tRPC mutation operations that use POST requests (create, update, delete)
- **Behavior:** Requests hang without timing out or returning errors

### Code Configuration
Our tRPC client is configured with standard HTTP batch links:

```typescript
httpBatchLink({
  transformer: SuperJSON,
  url: getBaseUrl() + "/api/trpc",
  headers: () => {
    const headers = new Headers();
    headers.set("x-trpc-source", "nextjs-react");
    return headers;
  },
})
```

Our API route handler uses the standard fetch handler:

```typescript
const handler = (req: NextRequest) =>
  fetchRequestHandler({
    endpoint: "/api/trpc",
    req,
    router: appRouter,
    createContext: () => createContext(req),
    onError: // error handling
  });

export { handler as GET, handler as POST };
```