Phase 8: optional accounts, per-user data, shared demo key

Guest-first multi-user mode behind AIDND_MULTI_USER (local installs
unchanged): signed-cookie guest sessions bootstrapped by /api/auth/me,
register upgrades the guest in place, login/logout, per-IP rate limits.
Every router scoped by user_id; Settings become per-user with the API
key Fernet-encrypted at rest and write-only through the API. Users
without a key get a server-funded demo key (OpenRouter free models,
20 turns/day, memory bank disabled on demo turns). Public read-only
demo scenarios (seed_demo.py); debug log restricted to local mode.
Frontend: auth modal + guest nudge, 401 re-establish/retry, demo
banner and key management in Settings.

Migrations 13-23 adopt existing data under a local user and encrypt
stored keys. Verified: migration on a copy of real data.db, two-session
isolation + register/login via curl and Chrome, demo cap 429, live
OpenRouter turn through the encrypted-key path, vite build + oxlint.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KFsGHju9szibJJa2YJcdbg

frontend/src/App.jsx

@@ -1,6 +1,32 @@
+import { useEffect, useState } from 'react'
 import { NavLink, Outlet } from 'react-router-dom'
+import { api } from './api'
+import { AuthModal } from './components'
 
 export default function App() {
+  // null until /auth/me resolves; in local mode multi_user=false hides all auth UI.
+  const [me, setMe] = useState(null)
+  const [authMode, setAuthMode] = useState(null) // 'register' | 'login' | null
+
+  useEffect(() => {
+    api.getMe().then(setMe).catch(() => {})
+  }, [])
+
+  const onAuthed = (newMe, mode) => {
+    setAuthMode(null)
+    if (mode === 'login') {
+      // Different user now — reload so every page refetches its scoped data.
+      window.location.reload()
+    } else {
+      setMe(newMe) // register upgrades the same user in place; data unchanged
+    }
+  }
+
+  const logout = async () => {
+    try { await api.logout() } catch { /* already logged out */ }
+    window.location.reload()
+  }
+
   return (
     <>
       <nav className="topnav">
@@ -17,8 +43,27 @@ export default function App() {
         <NavLink to="/settings" className={({ isActive }) => `navlink${isActive ? ' active' : ''}`}>
           Settings
         </NavLink>
+        {me?.multi_user && (
+          <div className="nav-account">
+            {me.is_guest ? (
+              <>
+                <span className="guest-nudge">Playing as guest — sign up to keep your adventures</span>
+                <button onClick={() => setAuthMode('login')}>Log in</button>
+                <button className="primary" onClick={() => setAuthMode('register')}>Sign up</button>
+              </>
+            ) : (
+              <>
+                <span className="account-email" title={me.email}>{me.email}</span>
+                <button onClick={logout}>Log out</button>
+              </>
+            )}
+          </div>
+        )}
       </nav>
-      <Outlet />
+      <Outlet context={{ me, setMe }} />
+      {authMode && (
+        <AuthModal mode={authMode} onClose={() => setAuthMode(null)} onAuthed={onAuthed} />
+      )}
     </>
   )
 }