fix(auth): auth pages reload when a session appears in another tab

Fixes #69

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/hooks/useSessionAppeared.ts

@@ -0,0 +1,33 @@
+import { useEffect } from 'react';
+import { getFallbackSession, subscribeSessionChanges } from '../state/sessions';
+
+/**
+ * #69 — `useSessionSync` (the full cross-tab session sync, with in-place token
+ * rotation handling) is mounted only inside the authenticated `ClientRoot`
+ * shell, so a tab parked on the login/register/OIDC-callback pages never
+ * learns that another tab just signed in. Left alone, that tab keeps showing
+ * the login form and, if submitted, starts a second device/session for the
+ * same account.
+ *
+ * This is a deliberately lighter watcher for the unauthenticated routes: it
+ * only cares about a session APPEARING where there was none before (a fresh
+ * login completed in another tab) and reloads so this tab picks up the
+ * authenticated shell instead. It does not need `useSessionSync`'s
+ * rotation/relogin handling since there is no running client here to keep in
+ * sync — do not import/duplicate that logic, just reload.
+ */
+export function useSessionAppeared(): void {
+  useEffect(() => {
+    // If we already have a session, there's nothing to watch for here — the
+    // authenticated shell's own useSessionSync takes over once mounted.
+    if (getFallbackSession()) return undefined;
+
+    const unsubscribe = subscribeSessionChanges((session) => {
+      if (session) {
+        window.location.reload();
+      }
+    });
+
+    return unsubscribe;
+  }, []);
+}

src/app/pages/App.tsx

@@ -26,6 +26,7 @@ import { settingsAtom } from '../state/settings';
 import { isWithinTimeWindow } from '../utils/timeWindow';
 import { LotusToastContainer } from '../features/toast/LotusToastContainer';
 import { useTauriNotificationBadge } from '../hooks/useTauriNotificationBadge';
+import { useSessionAppeared } from '../hooks/useSessionAppeared';
 import { useTauriWindowChrome } from '../hooks/useTauriWindowChrome';
 import { isTauri } from '../hooks/useTauri';
 import { TitleBar } from '../features/desktop/TitleBar';
@@ -165,6 +166,12 @@ const queryClient = new QueryClient();
 function App() {
   const screenSize = useScreenSize();
   useCompositionEndTracking();
+  // #69 — cross-tab session sync (useSessionSync) only mounts inside the
+  // authenticated ClientRoot shell, so a tab still on the unauthenticated
+  // routes (login/register/OIDC callback) never learns that another tab just
+  // signed in. This lighter watcher covers that gap by reloading once a
+  // session appears where there was none.
+  useSessionAppeared();
 
   const portalContainer = document.getElementById('portalContainer') ?? undefined;