fix: restore admin panel after Stalwart v0.16 REST API removal

app/admin/layout.tsx

@@ -65,6 +65,7 @@ export default function AdminLayout({ children }: { children: React.ReactNode })
   const router = useRouter();
   const pathname = usePathname();
   const [authenticated, setAuthenticated] = useState<boolean | null>(null);
+  const [authError, setAuthError] = useState<string | null>(null);
   const [isStalwartAdmin, setIsStalwartAdmin] = useState(false);
   const { appLogoLightUrl, appLogoDarkUrl, loginLogoLightUrl, loginLogoDarkUrl } = useConfig();
   const resolvedTheme = useThemeStore((s) => s.resolvedTheme);
@@ -73,21 +74,15 @@ export default function AdminLayout({ children }: { children: React.ReactNode })
     : (appLogoLightUrl || appLogoDarkUrl || loginLogoLightUrl);
 
   useEffect(() => {
-    if (pathname !== '/admin/login') {
-      checkAuth();
-    }
-  // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, [pathname]);
-
-  function getJmapHeaders(): Record<string, string> {
-    return getActiveAccountSlotHeaders();
-  }
+    if (pathname === '/admin/login') return;
+    let cancelled = false;
 
     async function checkAuth() {
       try {
-      const jmapHeaders = getJmapHeaders();
+        const jmapHeaders = getActiveAccountSlotHeaders();
         const res = await apiFetch('/api/admin/auth', { headers: jmapHeaders });
         const data = await res.json();
+        if (cancelled) return;
 
         const stalwartAdmin = data.stalwartAdmin === true;
         setIsStalwartAdmin(stalwartAdmin);
@@ -110,18 +105,29 @@ export default function AdminLayout({ children }: { children: React.ReactNode })
             headers: { 'Content-Type': 'application/json', ...jmapHeaders },
             body: JSON.stringify({ stalwartAuth: true }),
           });
+          if (cancelled) return;
           if (loginRes.ok) {
             setAuthenticated(true);
             return;
           }
+          const body = await loginRes.json().catch(() => ({}));
+          setAuthError(body?.error || `Admin auto-login failed (HTTP ${loginRes.status})`);
+          setAuthenticated(false);
+          return;
         }
 
         router.replace('/admin/login');
-    } catch {
-      router.replace('/admin/login');
+      } catch (err) {
+        if (cancelled) return;
+        setAuthError(err instanceof Error ? err.message : 'Network error during admin check');
+        setAuthenticated(false);
       }
     }
 
+    checkAuth();
+    return () => { cancelled = true; };
+  }, [pathname, router]);
+
   async function handleLogout() {
     await apiFetch('/api/admin/auth', { method: 'DELETE' });
     router.replace('/admin/login');
@@ -132,14 +138,6 @@ export default function AdminLayout({ children }: { children: React.ReactNode })
     return <>{children}</>;
   }
 
-  if (authenticated === null) {
-    return (
-      <div className="min-h-screen flex items-center justify-center bg-background">
-        <div className="animate-pulse text-muted-foreground text-sm">Loading...</div>
-      </div>
-    );
-  }
-
   return (
     <div className="min-h-screen flex bg-background">
       {/* Slim webmail nav rail */}
@@ -269,7 +267,18 @@ export default function AdminLayout({ children }: { children: React.ReactNode })
       {/* Main content */}
       <main className="flex-1 overflow-auto">
         <div className="max-w-4xl mx-auto p-6">
-          {children}
+          {authError ? (
+            <div className="rounded-lg border border-destructive/40 bg-destructive/10 p-4 text-sm text-destructive">
+              <p className="font-medium">Admin authentication failed</p>
+              <p className="mt-1 text-destructive/80">{authError}</p>
+            </div>
+          ) : authenticated === null ? (
+            <div className="py-12 text-center text-sm text-muted-foreground animate-pulse">
+              Loading admin panel…
+            </div>
+          ) : authenticated ? (
+            children
+          ) : null}
         </div>
       </main>
     </div>

components/layout/navigation-rail.tsx

@@ -8,7 +8,6 @@ import { icons as lucideIcons, type LucideIcon } from "lucide-react";
 import { useConfig } from "@/hooks/use-config";
 import { useThemeStore } from "@/stores/theme-store";
 import { usePathname, Link, useRouter } from "@/i18n/navigation";
-import NextLink from "next/link";
 import { useTranslations } from "next-intl";
 import { useCalendarStore } from "@/stores/calendar-store";
 import { useEmailStore } from "@/stores/email-store";
@@ -336,9 +335,9 @@ export function NavigationRail({
           );
         })}
 
-        {/* Admin (Stalwart admins) */}
+        {/* Admin (Stalwart admins) — hard nav because /admin lives outside the [locale] tree */}
         {isStalwartAdmin && (
-          <NextLink
+          <a
             href="/admin"
             className={cn(
               "flex flex-col items-center justify-center gap-1 py-2 px-1 min-h-[44px] grow shrink-0 basis-[64px]",
@@ -348,7 +347,7 @@ export function NavigationRail({
           >
             <Shield className="w-5 h-5" />
             <span className="text-[10px] font-medium leading-tight truncate max-w-full">{t("admin") || "Admin"}</span>
-          </NextLink>
+          </a>
         )}
 
         {/* Settings */}
@@ -514,13 +513,13 @@ export function NavigationRail({
       {/* Footer: Admin + Settings + Help + Storage Quota + Sign Out + Push Status */}
       <div className="mt-auto flex flex-col items-center gap-2 pb-3 px-1">
         {isStalwartAdmin && (
-          <NextLink
+          <a
             href="/admin"
             className="flex items-center justify-center w-10 h-10 rounded-md transition-colors text-muted-foreground hover:text-foreground hover:bg-muted"
             title={t("admin") || "Admin"}
           >
             <Shield className="w-[18px] h-[18px]" />
-          </NextLink>
+          </a>
         )}
 
         <Link