Ensure API contract integrity

// API Route implementation
export const POST = withError(async (request: Request) => {
  // 1. Validate request against documented schema
  const body = checkoutSessionSchema.parse(await request.json());
  
  // 2. Return appropriate status codes
  if (!session?.user?.email) {
    return NextResponse.json(
      { error: "Not authenticated" }, 
      { status: 401 }
    );
  }

  // 3. Include all required parameters
  const checkout = await stripe.checkout.sessions.create({
    customer: stripeCustomerId,
    success_url: `${env.NEXT_PUBLIC_BASE_URL}/api/stripe/success`,
    mode: "subscription",
    line_items: [{
      price: env.STRIPE_PRICE_ID,
      quantity: 1
    }]
  });

  return NextResponse.json({ checkout });
});

// OpenAPI documentation
registry.registerPath({
  method: "post",
  path: "/checkout",
  description: "Create checkout session",
  request: {
    body: {
      content: {
        "application/json": {
          schema: checkoutSessionSchema
        }
      }
    }
  },
  responses: {
    200: { description: "Success" },
    401: { description: "Not authenticated" }
  }
});