feat: add loading indicator when switching sessions

Show a spinner with 'Loading messages…' text while chat history
is being fetched during session switches, instead of briefly
flashing the empty welcome screen. Includes EN/FR i18n.

src/App.tsx

@@ -10,7 +10,7 @@ import { KeyboardShortcuts } from './components/KeyboardShortcuts';
 
 export default function App() {
   const {
-    status, messages, sessions, activeSession, isGenerating,
+    status, messages, sessions, activeSession, isGenerating, isLoadingHistory,
     sendMessage, abort, switchSession,
     authenticated, login, logout, connectError, isConnecting,
   } = useGateway();
@@ -77,7 +77,7 @@ export default function App() {
       <div className="flex-1 flex flex-col min-w-0" aria-hidden={sidebarOpen ? true : undefined}>
         <Header status={status} sessionKey={activeSession} onToggleSidebar={() => setSidebarOpen(!sidebarOpen)} activeSessionData={sessions.find(s => s.key === activeSession)} onLogout={logout} />
         <ConnectionBanner status={status} />
-        <Chat messages={messages} isGenerating={isGenerating} status={status} onSend={sendMessage} onAbort={abort} />
+        <Chat messages={messages} isGenerating={isGenerating} isLoadingHistory={isLoadingHistory} status={status} onSend={sendMessage} onAbort={abort} />
       </div>
       <KeyboardShortcuts open={shortcutsOpen} onClose={() => setShortcutsOpen(false)} />
     </div>

src/components/Chat.tsx

@@ -3,13 +3,14 @@ import { ChatMessageComponent } from './ChatMessage';
 import { ChatInput } from './ChatInput';
 import { TypingIndicator } from './TypingIndicator';
 import type { ChatMessage, ConnectionStatus } from '../types';
-import { Bot, ArrowDown } from 'lucide-react';
+import { Bot, ArrowDown, Loader2 } from 'lucide-react';
 import { useT } from '../hooks/useLocale';
 import { getLocale, type TranslationKey } from '../lib/i18n';
 
 interface Props {
   messages: ChatMessage[];
   isGenerating: boolean;
+  isLoadingHistory: boolean;
   status: ConnectionStatus;
   onSend: (text: string, attachments?: Array<{ mimeType: string; fileName: string; content: string }>) => void;
   onAbort: () => void;
@@ -63,7 +64,7 @@ function getDateKey(ts: number): string {
 /** Threshold in pixels — if the user is within this distance of the bottom, auto-scroll */
 const SCROLL_THRESHOLD = 150;
 
-export function Chat({ messages, isGenerating, status, onSend, onAbort }: Props) {
+export function Chat({ messages, isGenerating, isLoadingHistory, status, onSend, onAbort }: Props) {
   const t = useT();
   const bottomRef = useRef<HTMLDivElement>(null);
   const scrollContainerRef = useRef<HTMLDivElement>(null);
@@ -128,7 +129,13 @@ export function Chat({ messages, isGenerating, status, onSend, onAbort }: Props)
     <div className="flex-1 flex flex-col min-h-0 relative">
       <div ref={scrollContainerRef} className="flex-1 overflow-y-auto relative" role="log" aria-label={t('chat.messages')} aria-live="polite">
         <div className="max-w-4xl mx-auto py-4">
-          {messages.length === 0 && (
+          {messages.length === 0 && isLoadingHistory && (
+            <div className="flex flex-col items-center justify-center h-[60vh] text-zinc-500">
+              <Loader2 className="h-8 w-8 text-cyan-300/60 animate-spin mb-4" />
+              <div className="text-sm text-zinc-500">{t('chat.loadingHistory')}</div>
+            </div>
+          )}
+          {messages.length === 0 && !isLoadingHistory && (
             <div className="flex flex-col items-center justify-center h-[60vh] text-zinc-500">
               <div className="relative mb-6">
                 <div className="absolute -inset-4 rounded-3xl bg-gradient-to-r from-cyan-400/10 via-indigo-500/10 to-violet-500/10 blur-2xl" />

src/hooks/useGateway.ts

@@ -28,6 +28,7 @@ export function useGateway() {
   const [sessions, setSessions] = useState<Session[]>([]);
   const [activeSession, setActiveSession] = useState('agent:main:main');
   const [isGenerating, setIsGenerating] = useState(false);
+  const [isLoadingHistory, setIsLoadingHistory] = useState(false);
   const [authenticated, setAuthenticated] = useState<boolean | null>(null); // null = checking
   const [connectError, setConnectError] = useState<string | null>(null);
   const [isConnecting, setIsConnecting] = useState(false);
@@ -100,6 +101,7 @@ export function useGateway() {
   }, []);
 
   const loadHistory = useCallback(async (sessionKey: string) => {
+    setIsLoadingHistory(true);
     try {
       const res = await clientRef.current?.send('chat.history', { sessionKey, limit: 100 });
       const rawMsgs = res?.messages as Array<Record<string, unknown>> | undefined;
@@ -173,6 +175,8 @@ export function useGateway() {
       }
     } catch {
       // Silently ignore history load failures
+    } finally {
+      setIsLoadingHistory(false);
     }
   }, []);
 
@@ -388,7 +392,7 @@ export function useGateway() {
   }));
 
   return {
-    status, messages, sessions: enrichedSessions, activeSession, isGenerating,
+    status, messages, sessions: enrichedSessions, activeSession, isGenerating, isLoadingHistory,
     sendMessage, abort, switchSession, loadSessions,
     authenticated, login, logout, connectError, isConnecting,
   };

src/lib/i18n.ts

@@ -31,6 +31,7 @@ const en = {
   // Chat
   'chat.welcome': 'PinchChat',
   'chat.welcomeSub': 'Send a message to get started',
+  'chat.loadingHistory': 'Loading messages…',
   'chat.inputPlaceholder': 'Type a message…',
   'chat.inputLabel': 'Message',
   'chat.attachFile': 'Attach file',
@@ -106,6 +107,7 @@ const fr: Record<keyof typeof en, string> = {
 
   'chat.welcome': 'PinchChat',
   'chat.welcomeSub': 'Envoyez un message pour commencer',
+  'chat.loadingHistory': 'Chargement des messages…',
   'chat.inputPlaceholder': 'Tapez un message…',
   'chat.inputLabel': 'Message',
   'chat.attachFile': 'Joindre un fichier',