diff --git a/app/(dashboard)/_components/app-sidebar.tsx b/app/(dashboard)/_components/app-sidebar.tsx
index 0ad818a..cc2ad9a 100644
--- a/app/(dashboard)/_components/app-sidebar.tsx
+++ b/app/(dashboard)/_components/app-sidebar.tsx
@@ -1,5 +1,6 @@
 "use client";
 
+import { useState } from "react";
 import Link from "next/link";
 import { usePathname } from "next/navigation";
 import { ChevronRightIcon } from "lucide-react";
@@ -21,7 +22,9 @@ import {
   SidebarMenuSubButton,
   SidebarMenuSubItem,
 } from "@/components/ui/sidebar";
-import { navItems } from "./nav-items";
+import { navItems, type NavItem } from "./nav-items";
+
+type NavGroupItem = Extract<NavItem, { items: unknown }>;
 
 export function AppSidebar({ footer }: { footer: React.ReactNode }) {
   const pathname = usePathname();
@@ -36,33 +39,7 @@ export function AppSidebar({ footer }: { footer: React.ReactNode }) {
           <SidebarMenu className="gap-0.5">
             {navItems.map((item) =>
               "items" in item ? (
-                <Collapsible
-                  key={item.title}
-                  defaultOpen={item.items.some((sub) =>
-                    pathname.startsWith(sub.href),
-                  )}
-                  render={<SidebarMenuItem />}
-                >
-                  <CollapsibleTrigger render={<SidebarMenuButton />}>
-                    <item.icon />
-                    <span>{item.title}</span>
-                    <ChevronRightIcon className="ml-auto transition-transform group-data-panel-open/menu-button:rotate-90" />
-                  </CollapsibleTrigger>
-                  <CollapsibleContent>
-                    <SidebarMenuSub>
-                      {item.items.map((sub) => (
-                        <SidebarMenuSubItem key={sub.href}>
-                          <SidebarMenuSubButton
-                            render={<Link href={sub.href} />}
-                            isActive={pathname.startsWith(sub.href)}
-                          >
-                            <span>{sub.title}</span>
-                          </SidebarMenuSubButton>
-                        </SidebarMenuSubItem>
-                      ))}
-                    </SidebarMenuSub>
-                  </CollapsibleContent>
-                </Collapsible>
+                <NavGroup key={item.title} item={item} pathname={pathname} />
               ) : (
                 <SidebarMenuItem key={item.href}>
                   <SidebarMenuButton
@@ -82,3 +59,50 @@ export function AppSidebar({ footer }: { footer: React.ReactNode }) {
     </Sidebar>
   );
 }
+
+// Controlled karena sidebar tetap ter-mount antar navigasi; defaultOpen yang berubah memicu warning Base UI.
+function NavGroup({
+  item,
+  pathname,
+}: {
+  item: NavGroupItem;
+  pathname: string;
+}) {
+  const isActive = item.items.some((sub) => pathname.startsWith(sub.href));
+  const [open, setOpen] = useState(isActive);
+  const [prevActive, setPrevActive] = useState(isActive);
+
+  // Buka otomatis saat navigasi masuk ke grup ini, tanpa menutup grup yang dibuka manual.
+  if (isActive !== prevActive) {
+    setPrevActive(isActive);
+    if (isActive) setOpen(true);
+  }
+
+  return (
+    <Collapsible
+      open={open}
+      onOpenChange={setOpen}
+      render={<SidebarMenuItem />}
+    >
+      <CollapsibleTrigger render={<SidebarMenuButton />}>
+        <item.icon />
+        <span>{item.title}</span>
+        <ChevronRightIcon className="ml-auto transition-transform group-data-panel-open/menu-button:rotate-90" />
+      </CollapsibleTrigger>
+      <CollapsibleContent>
+        <SidebarMenuSub>
+          {item.items.map((sub) => (
+            <SidebarMenuSubItem key={sub.href}>
+              <SidebarMenuSubButton
+                render={<Link href={sub.href} />}
+                isActive={pathname.startsWith(sub.href)}
+              >
+                <span>{sub.title}</span>
+              </SidebarMenuSubButton>
+            </SidebarMenuSubItem>
+          ))}
+        </SidebarMenuSub>
+      </CollapsibleContent>
+    </Collapsible>
+  );
+}
diff --git a/app/not-found.tsx b/app/not-found.tsx
new file mode 100644
index 0000000..ce5167b
--- /dev/null
+++ b/app/not-found.tsx
@@ -0,0 +1,34 @@
+"use client";
+import { Button } from "@/components/ui/button";
+import Link from "next/link";
+import { useRouter } from "next/navigation";
+
+export default function NotFoundPage() {
+  const router = useRouter();
+  return (
+    <div className="grid min-h-svh place-items-center bg-background px-6 text-foreground">
+      <div className="w-full max-w-sm text-center">
+        <p className="font-mono text-xs tracking-[0.3em] text-muted-foreground uppercase">
+          Cleo Minimarket
+        </p>
+        <h1 className="mt-4 text-7xl font-semibold tracking-tighter tabular-nums">
+          404
+        </h1>
+        <p className="mt-3 text-lg font-medium">Halaman tidak ditemukan</p>
+        <p className="mt-2 text-sm text-muted-foreground">
+          Alamat yang dibuka tidak ada atau sudah dipindah.
+        </p>
+        <div className="mt-8 border-t border-dashed pt-6">
+          <Button
+            className="inline-flex h-10 items-center rounded-md bg-primary px-5 text-sm font-medium text-primary-foreground outline-none focus-visible:ring-2 focus-visible:ring-ring"
+            onClick={() => {
+              router.back();
+            }}
+          >
+            Kembali
+          </Button>
+        </div>
+      </div>
+    </div>
+  );
+}