No stub return values in non-trivial handlers

A handler whose body is only return Response.json({}) or return new Response() returns HTTP 200 without doing anything. The client accepts it as success, moves on, and logs no error. Orders never save, refunds never queue, webhooks never acknowledge — and the failure is invisible until a customer complains or a reconciliation job runs weeks later. This pattern ships constantly when AI scaffolds a route file it never finishes wiring.

Either implement the handler against the real data source or return an explicit 501 Not Implemented so clients see the gap. Never leave a stub that returns 200. Example at app/api/orders/route.ts:

export async function POST(req: Request) {
  const order = await prisma.order.create({ data: await req.json() })
  return Response.json(order, { status: 201 })
}