fixed

app/login/page.tsx

@@ -1,6 +1,14 @@
+import { redirect } from "next/navigation";
 import { loginAction } from "@/lib/actions";
+import { getSession } from "@/lib/auth";
+
+export default async function LoginPage() {
+  const session = await getSession();
+
+  if (session) {
+    redirect("/");
+  }
 
-export default function LoginPage() {
   return (
     <div className="grid">
       <section className="panel" style={{ maxWidth: 520 }}>