fix tab switching state issues

- Add useFocusEffect to calendar for automatic event reload on tab focus
- Create ChatStore (Zustand) for persistent chat messages across tab switches
- Replace local useState with store in chat screen

CLAUDE.md

@@ -90,6 +90,7 @@ src/
 └── stores/                     # Zustand state management
     ├── index.ts                # Re-exports all stores
     ├── AuthStore.ts            # user, token, isAuthenticated, login(), logout(), setToken()
+    ├── ChatStore.ts            # messages[], addMessage(), updateMessage(), clearMessages()
     └── EventsStore.ts          # events[], setEvents(), addEvent(), updateEvent(), deleteEvent()
 ```
 
@@ -298,7 +299,9 @@ MONGODB_URI=mongodb://root:mongoose@localhost:27017/calchat?authSource=admin
   - Orange dot indicator for days with events
   - Tap-to-open modal overlay showing EventCards for selected day
   - Supports events from adjacent months visible in grid
+  - Uses `useFocusEffect` for automatic reload on tab focus
 - Chat screen functional with FlashList, message sending, and event confirm/reject
+  - Messages persisted via ChatStore (survives tab switches)
 - `ApiClient`: get(), post(), put(), delete() implemented
 - `EventService`: getAll(), getById(), getByDateRange(), create(), update(), delete() - fully implemented
 - `ChatService`: sendMessage(), confirmEvent(convId, msgId, action, event?, eventId?, updates?), rejectEvent() - supports create/update/delete actions
@@ -306,6 +309,7 @@ MONGODB_URI=mongodb://root:mongoose@localhost:27017/calchat?authSource=admin
 - `ProposedEventCard`: Displays proposed events (title, date, description, recurring indicator) with confirm/reject buttons
 - `Themes.tsx`: Centralized color definitions including textPrimary, borderPrimary, eventIndicator
 - `EventsStore`: Zustand store with setEvents(), addEvent(), updateEvent(), deleteEvent() - stores ExpandedEvent[]
+- `ChatStore`: Zustand store with addMessage(), updateMessage(), clearMessages() - persists messages across tab switches
 - Auth screens (Login, Register), Event Detail, and Note screens exist as skeletons
 - AuthStore defined with `throw new Error('Not implemented')`
 

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

@@ -10,7 +10,14 @@ import {
 import { DAYS, MONTHS, Month, ExpandedEvent } from "@caldav/shared";
 import Header from "../../components/Header";
 import { EventCard } from "../../components/EventCard";
-import React, { useEffect, useMemo, useRef, useState } from "react";
+import React, {
+  useCallback,
+  useEffect,
+  useMemo,
+  useRef,
+  useState,
+} from "react";
+import { useFocusEffect } from "expo-router";
 import currentTheme from "../../Themes";
 import BaseBackground from "../../components/BaseBackground";
 import { FlashList } from "@shopify/flash-list";
@@ -26,9 +33,10 @@ const Calendar = () => {
 
   const { events, setEvents, deleteEvent } = useEventsStore();
 
-  // Load events when month/year changes
+  // Load events when tab gains focus or month/year changes
   // Include days from prev/next month that are visible in the grid
-  useEffect(() => {
+  useFocusEffect(
+    useCallback(() => {
       const loadEvents = async () => {
         try {
           // Calculate first visible day (up to 6 days before month start)
@@ -56,7 +64,8 @@ const Calendar = () => {
         }
       };
       loadEvents();
-  }, [monthIndex, currentYear, setEvents]);
+    }, [monthIndex, currentYear, setEvents]),
+  );
 
   // Group events by date (YYYY-MM-DD format)
   const eventsByDate = useMemo(() => {

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

@@ -5,6 +5,7 @@ import Header from "../../components/Header";
 import BaseBackground from "../../components/BaseBackground";
 import { FlashList } from "@shopify/flash-list";
 import { ChatService } from "../../services";
+import { useChatStore, MessageData } from "../../stores";
 import { ProposedEventChange } from "@caldav/shared";
 import { ProposedEventCard } from "../../components/ProposedEventCard";
 
@@ -24,17 +25,12 @@ type ChatMessageProps = {
   onReject?: () => void;
 };
 
-type MessageData = ChatMessageProps & {
-  id: string;
-  conversationId?: string;
-};
-
 type ChatInputProps = {
   onSend: (text: string) => void;
 };
 
 const Chat = () => {
-  const [messages, setMessages] = useState<MessageData[]>([]);
+  const { messages, addMessage, updateMessage } = useChatStore();
 
   const handleEventResponse = async (
     action: "confirm" | "reject",
@@ -43,11 +39,7 @@ const Chat = () => {
     proposedChange?: ProposedEventChange,
   ) => {
     // Mark message as responded (optimistic update)
-    setMessages((prev) =>
-      prev.map((msg) =>
-        msg.id === messageId ? { ...msg, respondedAction: action } : msg,
-      ),
-    );
+    updateMessage(messageId, { respondedAction: action });
 
     try {
       const response =
@@ -68,15 +60,11 @@ const Chat = () => {
         content: response.message.content,
         conversationId: response.conversationId,
       };
-      setMessages((prev) => [...prev, botMessage]);
+      addMessage(botMessage);
     } catch (error) {
       console.error(`Failed to ${action} event:`, error);
       // Revert on error
-      setMessages((prev) =>
-        prev.map((msg) =>
-          msg.id === messageId ? { ...msg, respondedAction: undefined } : msg,
-        ),
-      );
+      updateMessage(messageId, { respondedAction: undefined });
     }
   };
 
@@ -87,7 +75,7 @@ const Chat = () => {
       side: "right",
       content: text,
     };
-    setMessages((prev) => [...prev, userMessage]);
+    addMessage(userMessage);
 
     try {
       // Fetch server response
@@ -101,7 +89,7 @@ const Chat = () => {
         proposedChange: response.message.proposedChange,
         conversationId: response.conversationId,
       };
-      setMessages((prev) => [...prev, botMessage]);
+      addMessage(botMessage);
     } catch (error) {
       console.error("Failed to send message:", error);
     }

apps/client/src/stores/ChatStore.ts

@@ -0,0 +1,37 @@
+import { create } from "zustand";
+import { ProposedEventChange } from "@caldav/shared";
+
+type BubbleSide = "left" | "right";
+
+export type MessageData = {
+  id: string;
+  side: BubbleSide;
+  content: string;
+  proposedChange?: ProposedEventChange;
+  respondedAction?: "confirm" | "reject";
+  conversationId?: string;
+};
+
+interface ChatState {
+  messages: MessageData[];
+  addMessage: (message: MessageData) => void;
+  updateMessage: (id: string, updates: Partial<MessageData>) => void;
+  clearMessages: () => void;
+}
+
+export const useChatStore = create<ChatState>((set) => ({
+  messages: [],
+  addMessage: (message: MessageData) => {
+    set((state) => ({ messages: [...state.messages, message] }));
+  },
+  updateMessage: (id: string, updates: Partial<MessageData>) => {
+    set((state) => ({
+      messages: state.messages.map((msg) =>
+        msg.id === id ? { ...msg, ...updates } : msg,
+      ),
+    }));
+  },
+  clearMessages: () => {
+    set({ messages: [] });
+  },
+}));

apps/client/src/stores/index.ts

@@ -1,2 +1,3 @@
 export { useAuthStore } from "./AuthStore";
+export { useChatStore, type MessageData } from "./ChatStore";
 export { useEventsStore } from "./EventsStore";