feat(tauri): proactive update notifications via toast (P5-40)

TauriUpdateFeature component in ClientNonUIFeatures checks for updates
on mount and every 12h (skips if checked within the window). On update
available, fires a Lotus toast: "Lotus Chat vX.Y.Z is ready to install."
Clicking the toast calls install(). No-op on web (isTauri guard).

Also adds optional onClick to ToastNotif type and wires it in
LotusToastContainer so custom click handlers can skip hash navigation.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

LOTUS_TODO.md

@@ -349,7 +349,7 @@ Themes:
 
 ---
 
-### [ ] P5-40 · Desktop — Proactive Update Notifications (Tauri)
+### [x] P5-40 · Desktop — Proactive Update Notifications (Tauri) ⚠️ UNTESTED (requires Tauri build)
 
 **What:** Automatically check for app updates on launch and periodically during long sessions. If an update is available, show an in-app toast or badge (e.g., on the Settings icon) to alert the user without requiring a manual check in settings.  
 **Mechanism:** Use the `useTauriUpdater` hook in a global component like `ClientNonUIFeatures.tsx`.  

src/app/features/toast/LotusToastContainer.tsx

@@ -41,8 +41,12 @@ function ToastCard({ toast }: ToastCardProps) {
   }, [dismiss, toast.id]);
 
   const handleCardClick = () => {
-    // window.location.hash setter auto-prepends '#', so values must not include it
-    window.location.hash = toast.hashPath ?? `/room/${toast.roomId}`;
+    if (toast.onClick) {
+      toast.onClick();
+    } else {
+      // window.location.hash setter auto-prepends '#', so values must not include it
+      window.location.hash = toast.hashPath ?? `/room/${toast.roomId}`;
+    }
     dismiss(toast.id);
   };
 

src/app/pages/client/ClientNonUIFeatures.tsx

@@ -37,6 +37,7 @@ import { usePresenceUpdater } from '../../hooks/usePresenceUpdater';
 import { useDeepLinkNavigate } from '../../hooks/useDeepLinkNavigate';
 import { toastQueueAtom } from '../../state/toast';
 import { useReminders } from '../../hooks/useReminders';
+import { useTauriUpdater } from '../../hooks/useTauriUpdater';
 
 function isInQuietHours(start: string, end: string): boolean {
   const now = new Date();
@@ -429,6 +430,46 @@ function ReminderMonitor() {
   return null;
 }
 
+const TAURI_UPDATE_CHECK_INTERVAL = 12 * 60 * 60_000; // 12 hours
+const TAURI_UPDATE_LAST_CHECK_KEY = 'lotus.tauriUpdateLastCheck';
+
+function TauriUpdateFeature() {
+  const { isTauri, status, check, install } = useTauriUpdater();
+  const setToast = useSetAtom(toastQueueAtom);
+  const firedRef = useRef<string | null>(null);
+
+  useEffect(() => {
+    if (!isTauri) return;
+
+    const runCheck = () => {
+      const last = Number(localStorage.getItem(TAURI_UPDATE_LAST_CHECK_KEY) ?? '0');
+      if (Date.now() - last < TAURI_UPDATE_CHECK_INTERVAL) return;
+      localStorage.setItem(TAURI_UPDATE_LAST_CHECK_KEY, String(Date.now()));
+      check();
+    };
+
+    runCheck();
+    const interval = setInterval(runCheck, TAURI_UPDATE_CHECK_INTERVAL);
+    return () => clearInterval(interval);
+  }, [isTauri, check]);
+
+  useEffect(() => {
+    if (status.state !== 'available') return;
+    if (firedRef.current === status.version) return;
+    firedRef.current = status.version;
+    setToast({
+      id: `tauri-update-${status.version}`,
+      displayName: 'Update Available',
+      body: `Lotus Chat ${status.version} is ready to install.`,
+      roomName: 'System',
+      roomId: '',
+      onClick: install,
+    });
+  }, [status, setToast, install]);
+
+  return null;
+}
+
 function LotusDenoiseFeature() {
   const setToast = useSetAtom(toastQueueAtom);
 
@@ -465,6 +506,7 @@ export function ClientNonUIFeatures({ children }: ClientNonUIFeaturesProps) {
       <InviteNotifications />
       <MessageNotifications />
       <ReminderMonitor />
+      <TauriUpdateFeature />
       <LotusDenoiseFeature />
       <DeepLinkNavigator />
       {children}

src/app/state/toast.ts

@@ -8,6 +8,7 @@ export type ToastNotif = {
   roomName: string;
   roomId: string;
   hashPath?: string; // overrides window.location.hash navigation when set
+  onClick?: () => void; // custom click handler; skips hash navigation when set
 };
 
 const baseAtom = atom<ToastNotif[]>([]);