refactor: add AuthGuard component and fix API client empty response handling

- Add reusable AuthGuard component for protected routes
- Move auth logic from index.tsx to (tabs)/_layout.tsx via AuthGuard
- Fix ApiClient to handle empty responses (204 No Content)
- Use useFocusEffect in chat.tsx to load messages after auth is ready
- Extract getDateKey() helper function in calendar.tsx

CLAUDE.md

@@ -81,6 +81,7 @@ src/
 │   └── note/
 │       └── [id].tsx            # Note editor for event (dynamic route)
 ├── components/
+│   ├── AuthGuard.tsx           # Auth wrapper: loads user, shows loading, redirects if unauthenticated
 │   ├── BaseBackground.tsx      # Common screen wrapper (themed)
 │   ├── BaseButton.tsx          # Reusable button component (themed, supports children)
 │   ├── Header.tsx              # Header component (themed)
@@ -97,7 +98,7 @@ src/
 │   └── logger.ts               # react-native-logs config (apiLogger, storeLogger)
 ├── services/
 │   ├── index.ts                # Re-exports all services
-│   ├── ApiClient.ts            # HTTP client with X-User-Id header injection, request logging
+│   ├── ApiClient.ts            # HTTP client with X-User-Id header injection, request logging, handles empty responses (204)
 │   ├── AuthService.ts          # login(), register(), logout() - calls API and updates AuthStore
 │   ├── EventService.ts         # getAll(), getById(), getByDateRange(), create(), update(), delete()
 │   └── ChatService.ts          # sendMessage(), confirmEvent(), rejectEvent(), getConversations(), getConversation()
@@ -112,6 +113,13 @@ src/
 
 **Routing:** Tab-based navigation with Chat, Calendar, and Settings as main screens. Auth screens (login, register) outside tabs. Dynamic routes for event detail and note editing.
 
+**Authentication Flow:**
+- `AuthGuard` component wraps the tab layout in `(tabs)/_layout.tsx`
+- On app start, `AuthGuard` calls `loadStoredUser()` and shows loading indicator
+- If not authenticated, redirects to `/login`
+- `index.tsx` simply redirects to `/(tabs)/chat` - AuthGuard handles the rest
+- This pattern handles Expo Router's navigation state caching (avoids race conditions)
+
 ### Theme System
 
 The app supports multiple themes (light/dark) via a reactive Zustand store.
@@ -412,12 +420,14 @@ NODE_ENV=development        # development = pretty logs, production = JSON
 - **Authentication fully implemented:**
   - `AuthStore`: Manages user state with expo-secure-store (native) / localStorage (web)
   - `AuthService`: login(), register(), logout() - calls backend API
-  - `ApiClient`: Automatically injects X-User-Id header for authenticated requests
+  - `ApiClient`: Automatically injects X-User-Id header for authenticated requests, handles empty responses (204)
+  - `AuthGuard`: Reusable component that wraps protected routes - loads user, shows loading, redirects if unauthenticated
   - Login screen: Supports email OR userName login
   - Register screen: Email validation, checks for existing email/userName
   - `AuthButton`: Reusable button component with themed shadow
   - `Header`: Themed header component (logout moved to Settings)
-  - `index.tsx`: Auth redirect - checks stored user on app start
+  - `(tabs)/_layout.tsx`: Wraps tabs with AuthGuard for protected access
+  - `index.tsx`: Simple redirect to chat (AuthGuard handles auth)
 - **Theme system fully implemented:**
   - `ThemeStore`: Zustand store with theme state and setTheme()
   - `Themes.tsx`: THEMES object with defaultLight/defaultDark variants
@@ -438,7 +448,7 @@ NODE_ENV=development        # development = pretty logs, production = JSON
   - Arrow navigation between proposals with "Event X von Y" counter
   - Each proposal individually confirmable/rejectable
   - **Typing indicator**: Animated dots (. .. ...) shown after 500ms delay while waiting for AI response
-  - Messages persisted to database via ChatService and loaded on mount
+  - Messages persisted to database via ChatService, loaded via `useFocusEffect` when screen gains focus
   - Tracks conversationId for message continuity across sessions
   - ChatStore with addMessages() for bulk loading, chatMessageToMessageData() helper
   - KeyboardAvoidingView for proper keyboard handling (iOS padding, Android height)

apps/client/src/app/(tabs)/_layout.tsx

@@ -1,11 +1,13 @@
 import { Ionicons } from "@expo/vector-icons";
 import { Tabs } from "expo-router";
 import { useThemeStore } from "../../stores/ThemeStore";
+import { AuthGuard } from "../../components/AuthGuard";
 
 export default function TabLayout() {
   const { theme } = useThemeStore();
   return (
-    <Tabs
+    <AuthGuard>
+      <Tabs
       screenOptions={{
         headerShown: false,
         tabBarActiveTintColor: theme.chatBot,
@@ -40,6 +42,7 @@ export default function TabLayout() {
           ),
         }}
       />
-    </Tabs>
+      </Tabs>
+    </AuthGuard>
   );
 }

apps/client/src/app/(tabs)/calendar.tsx

@@ -33,6 +33,14 @@ type MonthItem = {
   label: string; // e.g. "January 2024"
 };
 
+/**
+ * Formats a Date object to a string key in YYYY-MM-DD format.
+ * Used for grouping and looking up events by date.
+ */
+const getDateKey = (date: Date): string => {
+  return `${date.getFullYear()}-${String(date.getMonth() + 1).padStart(2, "0")}-${String(date.getDate()).padStart(2, "0")}`;
+};
+
 const generateMonths = (
   centerYear: number,
   centerMonth: number,
@@ -108,7 +116,7 @@ const Calendar = () => {
     const map = new Map<string, ExpandedEvent[]>();
     events.forEach((e) => {
       const date = new Date(e.occurrenceStart);
-      const key = `${date.getFullYear()}-${String(date.getMonth() + 1).padStart(2, "0")}-${String(date.getDate()).padStart(2, "0")}`;
+      const key = getDateKey(date);
       if (!map.has(key)) map.set(key, []);
       map.get(key)!.push(e);
     });
@@ -157,7 +165,7 @@ const Calendar = () => {
             deleteEvent(event.id);
             // Close overlay if no more events for this date
             if (selectedDate) {
-              const dateKey = `${selectedDate.getFullYear()}-${String(selectedDate.getMonth() + 1).padStart(2, "0")}-${String(selectedDate.getDate()).padStart(2, "0")}`;
+              const dateKey = getDateKey(selectedDate);
               const remainingEvents = eventsByDate.get(dateKey) || [];
               if (remainingEvents.length <= 1) {
                 setSelectedDate(null);
@@ -175,7 +183,7 @@ const Calendar = () => {
   // Get events for selected date
   const selectedDateEvents = useMemo(() => {
     if (!selectedDate) return [];
-    const key = `${selectedDate.getFullYear()}-${String(selectedDate.getMonth() + 1).padStart(2, "0")}-${String(selectedDate.getDate()).padStart(2, "0")}`;
+    const key = getDateKey(selectedDate);
     return eventsByDate.get(key) || [];
   }, [selectedDate, eventsByDate]);
 
@@ -597,10 +605,6 @@ const CalendarGrid = (props: CalendarGridProps) => {
     return date;
   };
 
-  const getDateKey = (date: Date): string => {
-    return `${date.getFullYear()}-${String(date.getMonth() + 1).padStart(2, "0")}-${String(date.getDate()).padStart(2, "0")}`;
-  };
-
   return (
     <View
       className="h-full flex-1 flex-col flex-wrap gap-2 p-2"

apps/client/src/app/(tabs)/chat.tsx

@@ -8,13 +8,15 @@ import {
   Keyboard,
 } from "react-native";
 import { useThemeStore } from "../../stores/ThemeStore";
-import React, { useState, useRef, useEffect } from "react";
+import React, { useState, useRef, useEffect, useCallback } from "react";
+import { useFocusEffect } from "expo-router";
 import Header from "../../components/Header";
 import BaseBackground from "../../components/BaseBackground";
 import { FlashList } from "@shopify/flash-list";
 import { ChatService } from "../../services";
 import {
   useChatStore,
+  useAuthStore,
   chatMessageToMessageData,
   MessageData,
 } from "../../stores";
@@ -45,6 +47,7 @@ type ChatInputProps = {
 const TYPING_INDICATOR_DELAY_MS = 500;
 
 const Chat = () => {
+  const { isAuthenticated, isLoading: isAuthLoading } = useAuthStore();
   const {
     messages,
     addMessage,
@@ -68,27 +71,31 @@ const Chat = () => {
     return () => keyboardDidShow.remove();
   }, []);
 
-  // Load existing messages from database on mount
-  useEffect(() => {
-    const fetchMessages = async () => {
-      try {
-        const conversationSummaries = await ChatService.getConversations();
-        if (conversationSummaries.length > 0) {
-          const conversationId = conversationSummaries[0].id;
-          setCurrentConversationId(conversationId);
+  // Load existing messages from database once authenticated and screen is focused
+  useFocusEffect(
+    useCallback(() => {
+      if (isAuthLoading || !isAuthenticated) return;
 
-          const serverMessages =
-            await ChatService.getConversation(conversationId);
-          const clientMessages = serverMessages.map(chatMessageToMessageData);
-          addMessages(clientMessages);
-          scrollToEnd();
+      const fetchMessages = async () => {
+        try {
+          const conversationSummaries = await ChatService.getConversations();
+          if (conversationSummaries.length > 0) {
+            const conversationId = conversationSummaries[0].id;
+            setCurrentConversationId(conversationId);
+
+            const serverMessages =
+              await ChatService.getConversation(conversationId);
+            const clientMessages = serverMessages.map(chatMessageToMessageData);
+            addMessages(clientMessages);
+            scrollToEnd();
+          }
+        } catch (error) {
+          console.error("Failed to load messages:", error);
         }
-      } catch (error) {
-        console.error("Failed to load messages:", error);
-      }
-    };
-    fetchMessages();
-  }, []);
+      };
+      fetchMessages();
+    }, [isAuthLoading, isAuthenticated]),
+  );
 
   const scrollToEnd = () => {
     setTimeout(() => {
@@ -283,6 +290,7 @@ const ChatInput = ({ onSend }: ChatInputProps) => {
         className="flex-1 border border-solid rounded-2xl px-3 py-2 mr-2"
         style={{
           backgroundColor: theme.messageBorderBg,
+          color: theme.textPrimary,
           minHeight: MIN_INPUT_HEIGHT,
           maxHeight: MAX_INPUT_HEIGHT,
           textAlignVertical: "top",

apps/client/src/app/index.tsx

@@ -1,35 +1,6 @@
-import { useEffect } from "react";
-import { View, ActivityIndicator } from "react-native";
 import { Redirect } from "expo-router";
-import { useAuthStore } from "../stores";
-import { useThemeStore } from "../stores/ThemeStore";
 
 export default function Index() {
-  const { isAuthenticated, isLoading, loadStoredUser } = useAuthStore();
-  const { theme } = useThemeStore();
-
-  useEffect(() => {
-    loadStoredUser();
-  }, [loadStoredUser]);
-
-  if (isLoading) {
-    return (
-      <View
-        style={{
-          flex: 1,
-          justifyContent: "center",
-          alignItems: "center",
-          backgroundColor: theme.primeBg,
-        }}
-      >
-        <ActivityIndicator size="large" color={theme.chatBot} />
-      </View>
-    );
-  }
-
-  if (isAuthenticated) {
-    return <Redirect href="/(tabs)/chat" />;
-  }
-
-  return <Redirect href="/login" />;
+  // AuthGuard in (tabs)/_layout.tsx handles authentication
+  return <Redirect href="/(tabs)/chat" />;
 }

apps/client/src/components/AuthGuard.tsx

@@ -0,0 +1,46 @@
+import { useEffect, ReactNode } from "react";
+import { View, ActivityIndicator } from "react-native";
+import { Redirect } from "expo-router";
+import { useAuthStore } from "../stores";
+import { useThemeStore } from "../stores/ThemeStore";
+
+type AuthGuardProps = {
+  children: ReactNode;
+};
+
+/**
+ * Wraps content that requires authentication.
+ * - Loads stored user on mount
+ * - Shows loading indicator while checking auth state
+ * - Redirects to login if not authenticated
+ * - Renders children if authenticated
+ */
+export const AuthGuard = ({ children }: AuthGuardProps) => {
+  const { theme } = useThemeStore();
+  const { isAuthenticated, isLoading, loadStoredUser } = useAuthStore();
+
+  useEffect(() => {
+    loadStoredUser();
+  }, [loadStoredUser]);
+
+  if (isLoading) {
+    return (
+      <View
+        style={{
+          flex: 1,
+          justifyContent: "center",
+          alignItems: "center",
+          backgroundColor: theme.primeBg,
+        }}
+      >
+        <ActivityIndicator size="large" color={theme.chatBot} />
+      </View>
+    );
+  }
+
+  if (!isAuthenticated) {
+    return <Redirect href="/login" />;
+  }
+
+  return <>{children}</>;
+};

apps/client/src/services/ApiClient.ts

@@ -55,7 +55,12 @@ async function request<T>(
     }
 
     apiLogger.debug(`${method} ${endpoint} - ${response.status} (${duration}ms)`);
-    return response.json();
+
+    const text = await response.text();
+    if (!text) {
+      return undefined as T;
+    }
+    return JSON.parse(text);
   } catch (error) {
     const duration = Math.round(performance.now() - start);
     apiLogger.error(`${method} ${endpoint} failed (${duration}ms): ${error}`);