feat: improve AI Chat UX, add notebook summary, and fix shared/reminders routing

memento-note/lib/i18n/LanguageProvider.tsx

@@ -31,15 +31,23 @@ export function LanguageProvider({ children, initialLanguage = 'en', initialTran
   initialLanguage?: SupportedLanguage
   initialTranslations?: Translations
 }) {
-  // Use server-provided initialLanguage for the first render to prevent hydration mismatch.
+  // Use server-provided initialLanguage and translations for the first render 
+  // to ensure client hydration matches server HTML exactly.
   const [language, setLanguageState] = useState<SupportedLanguage>(initialLanguage)
 
-  // Start with server-provided translations or English fallback
-  const [translations, setTranslations] = useState<Translations>(
-    (initialTranslations || enTranslations) as unknown as Translations
-  )
+  // Start with server-provided translations or fallback to English ONLY if it's the requested language
+  const [translations, setTranslations] = useState<Translations>(() => {
+    if (initialTranslations) return initialTranslations
+    return enTranslations as unknown as Translations
+  })
 
   const cacheRef = useRef<Map<SupportedLanguage, Translations>>(new Map())
+  
+  // Initialize cache with initial translations to prevent redundant loading
+  if (initialTranslations && !cacheRef.current.has(initialLanguage)) {
+    cacheRef.current.set(initialLanguage, initialTranslations)
+  }
+
   const isFirstRender = useRef(true)
 
   // Load saved preference from localStorage AFTER hydration
@@ -74,6 +82,7 @@ export function LanguageProvider({ children, initialLanguage = 'en', initialTran
   const setLanguage = useCallback((lang: SupportedLanguage) => {
     setLanguageState(lang)
     localStorage.setItem('user-language', lang)
+    document.cookie = `user-language=${lang};path=/;max-age=${60 * 60 * 24 * 365};samesite=lax`
     updateDocumentDirection(lang)
   }, [])
 

memento-note/lib/i18n/detect-user-language.ts

@@ -1,6 +1,7 @@
 /**
  * Detect user's preferred language.
  * Priority:
+ * 0. user-language cookie (explicit user choice, synced with localStorage)
  * 1. Most common language among user's notes (DB GROUP BY)
  * 2. Browser language hint (passed from server component via Accept-Language)
  * 3. Default: 'en'
@@ -8,7 +9,7 @@
 
 import { auth } from '@/auth'
 import { prisma } from '@/lib/prisma'
-import { unstable_cache } from 'next/cache'
+import { unstable_cache, cookies } from 'next/cache'
 import { SupportedLanguage } from './load-translations'
 
 const SUPPORTED_LANGUAGES = new Set(['en', 'fr', 'es', 'de', 'fa', 'it', 'pt', 'ru', 'zh', 'ja', 'ko', 'ar', 'hi', 'nl', 'pl'])
@@ -79,6 +80,16 @@ const getCachedUserLanguage = unstable_cache(
  *                               Should be passed from server components that have access to headers().
  */
 export async function detectUserLanguage(browserLanguageHint?: SupportedLanguage | null): Promise<SupportedLanguage> {
+  // 0. Cookie has highest priority — set by the client when user picks a language.
+  //    This guarantees server and client agree on the language (no hydration mismatch).
+  try {
+    const cookieStore = await cookies()
+    const cookieLang = cookieStore.get('user-language')?.value
+    if (cookieLang && SUPPORTED_LANGUAGES.has(cookieLang)) {
+      return cookieLang as SupportedLanguage
+    }
+  } catch {}
+
   const session = await auth()
 
   if (!session?.user?.id) {