fix architecture and write new tests

apps/marketplace/src/middleware.ts

@@ -4,6 +4,12 @@ import type { NextRequest } from 'next/server'
 const SHARED_LANGUAGE_COOKIE = 'rentaldrivego-language'
 const MARKETPLACE_LANGUAGE_COOKIE = 'marketplace-language'
 
+
+function rejectInternalSubrequest(request: NextRequest): NextResponse | null {
+  if (!request.headers.has('x-middleware-subrequest')) return null
+  return new NextResponse('Unsupported internal request header', { status: 400 })
+}
+
 function isValidLanguage(val: string | null | undefined): val is 'en' | 'fr' | 'ar' {
   return val === 'en' || val === 'fr' || val === 'ar'
 }
@@ -18,6 +24,9 @@ function detectFromAcceptLanguage(header: string | null): 'en' | 'fr' | 'ar' {
 }
 
 export function middleware(request: NextRequest) {
+  const rejected = rejectInternalSubrequest(request)
+  if (rejected) return rejected
+
   const sharedLang = request.cookies.get(SHARED_LANGUAGE_COOKIE)?.value
 
   // Already has the canonical language cookie — no action needed