fix(chat): guard the chat page prefetch behind the chat flag

Author: waleedlatif1

apps/sim/app/workspace/[workspaceId]/chat/[chatId]/page.tsx

@@ -1,7 +1,9 @@
 import { Suspense } from 'react'
 import { dehydrate, HydrationBoundary } from '@tanstack/react-query'
 import type { Metadata } from 'next'
+import { notFound } from 'next/navigation'
 import { getSession } from '@/lib/auth'
+import { isChatEnabled } from '@/lib/core/config/env-flags'
 import { getQueryClient } from '@/app/_shell/providers/get-query-client'
 import { Home } from '@/app/workspace/[workspaceId]/home/home'
 import { HomeFallback } from '@/app/workspace/[workspaceId]/home/home-fallback'
@@ -20,6 +22,12 @@ interface ChatPageProps {
 }
 
 export default async function ChatPage({ params }: ChatPageProps) {
+  // The layout 404s too, but pages and layouts resolve concurrently — without this
+  // the prefetch below still fires on its way out.
+  if (!isChatEnabled) {
+    notFound()
+  }
+
   const [{ workspaceId, chatId }, session] = await Promise.all([params, getSession()])
   const userId = session?.user?.id
   const queryClient = getQueryClient()