fix: clean stale auth state on login/setup, unify language switcher

- LoginPage/SetupPage: clear localStorage auth tokens on mount
- AuthContext: clear onboarding state on register, invalidate config on logout
- Extract shared LanguageSwitcher component for consistent UI
- Merge duplicate config import in AuthContext

web/src/components/auth/LoginPage.tsx

@@ -5,6 +5,7 @@ import { useAuth } from '../../contexts/AuthContext'
 import { useLanguage } from '../../contexts/LanguageContext'
 import { t } from '../../i18n/translations'
 import { DeepVoidBackground } from '../common/DeepVoidBackground'
+import { LanguageSwitcher } from '../common/LanguageSwitcher'
 import { OnboardingModeSelector } from './OnboardingModeSelector'
 import type { UserMode } from '../../lib/onboarding'
 
@@ -19,6 +20,14 @@ export function LoginPage() {
   const [expiredToastId, setExpiredToastId] = useState<string | number | null>(null)
   const [mode, setMode] = useState<UserMode>('beginner')
 
+  // Clean up stale auth state once on mount
+  useEffect(() => {
+    localStorage.removeItem('auth_token')
+    localStorage.removeItem('auth_user')
+    localStorage.removeItem('user_id')
+  }, [])
+
+  // Show session-expired toast (re-runs on language change to update text)
   useEffect(() => {
     if (sessionStorage.getItem('from401') === 'true') {
       const id = toast.warning(t('sessionExpired', language), { duration: Infinity })
@@ -44,6 +53,8 @@ export function LoginPage() {
 
   return (
     <DeepVoidBackground disableAnimation>
+      <LanguageSwitcher />
+
       <div className="flex-1 flex items-center justify-center px-4 py-16">
         <div className="w-full max-w-sm">
 

web/src/components/common/LanguageSwitcher.tsx

@@ -0,0 +1,34 @@
+import React from 'react'
+import { Globe } from 'lucide-react'
+import { useLanguage } from '../../contexts/LanguageContext'
+import type { Language } from '../../i18n/translations'
+
+const languages: { code: Language; label: string }[] = [
+  { code: 'zh', label: '中文' },
+  { code: 'en', label: 'EN' },
+  { code: 'id', label: 'ID' },
+]
+
+export function LanguageSwitcher() {
+  const { language, setLanguage } = useLanguage()
+
+  return (
+    <div className="absolute top-4 right-4 z-50 flex items-center gap-1 rounded-lg p-1 border border-white/10 bg-white/5 backdrop-blur-sm">
+      <Globe size={14} className="text-zinc-500 ml-1.5 mr-0.5" />
+      {languages.map(({ code, label }) => (
+        <button
+          key={code}
+          type="button"
+          onClick={() => setLanguage(code)}
+          className={`px-2.5 py-1 rounded text-xs font-semibold transition-all ${
+            language === code
+              ? 'bg-nofx-gold/15 text-nofx-gold'
+              : 'text-zinc-500 hover:text-zinc-300 bg-transparent'
+          }`}
+        >
+          {label}
+        </button>
+      ))}
+    </div>
+  )
+}

web/src/components/modals/SetupPage.tsx

@@ -1,10 +1,11 @@
-import React, { useState } from 'react'
-import { Eye, EyeOff, Globe } from 'lucide-react'
+import React, { useState, useEffect } from 'react'
+import { Eye, EyeOff } from 'lucide-react'
 import { useAuth } from '../../contexts/AuthContext'
 import { invalidateSystemConfig } from '../../lib/config'
 import { OnboardingModeSelector } from '../auth/OnboardingModeSelector'
 import type { UserMode } from '../../lib/onboarding'
 import { useLanguage } from '../../contexts/LanguageContext'
+import { LanguageSwitcher } from '../common/LanguageSwitcher'
 import type { Language } from '../../i18n/translations'
 
 const labels = {
@@ -49,14 +50,8 @@ const labels = {
   },
 } as const
 
-const langOptions: { value: Language; label: string }[] = [
-  { value: 'en', label: 'English' },
-  { value: 'zh', label: '中文' },
-  { value: 'id', label: 'Bahasa' },
-]
-
 export function SetupPage() {
-  const { language, setLanguage } = useLanguage()
+  const { language } = useLanguage()
   const { register } = useAuth()
   const [email, setEmail] = useState('')
   const [password, setPassword] = useState('')
@@ -65,6 +60,15 @@ export function SetupPage() {
   const [loading, setLoading] = useState(false)
   const [mode, setMode] = useState<UserMode>('beginner')
 
+  // Clean up any stale auth/onboarding state on setup page load
+  useEffect(() => {
+    localStorage.removeItem('auth_token')
+    localStorage.removeItem('auth_user')
+    localStorage.removeItem('user_id')
+    localStorage.removeItem('nofx_beginner_onboarding_completed')
+    localStorage.removeItem('nofx_beginner_wallet_address')
+  }, [])
+
   const l = labels[language as keyof typeof labels] || labels.en
 
   const handleSubmit = async (e: React.FormEvent) => {
@@ -124,26 +128,7 @@ export function SetupPage() {
       {/* Blur overlay */}
       <div className="absolute inset-0 backdrop-blur-md bg-black/60" />
 
-      {/* Language switcher */}
-      <div className="fixed top-4 right-4 z-50">
-        <div className="flex items-center gap-1.5 rounded-xl border border-white/10 bg-white/5 backdrop-blur-sm px-2 py-1.5">
-          <Globe className="h-3.5 w-3.5 text-zinc-500" />
-          {langOptions.map((opt) => (
-            <button
-              key={opt.value}
-              type="button"
-              onClick={() => setLanguage(opt.value)}
-              className={`rounded-lg px-2 py-1 text-xs font-medium transition ${
-                language === opt.value
-                  ? 'bg-nofx-gold/15 text-nofx-gold'
-                  : 'text-zinc-500 hover:text-zinc-300'
-              }`}
-            >
-              {opt.label}
-            </button>
-          ))}
-        </div>
-      </div>
+      <LanguageSwitcher />
 
       {/* Modal card */}
       <div className="relative z-10 flex min-h-screen items-center justify-center px-4 py-16">

web/src/contexts/AuthContext.tsx

@@ -1,6 +1,6 @@
 import React, { createContext, useContext, useState, useEffect } from 'react'
 import { flushSync } from 'react-dom'
-import { getSystemConfig } from '../lib/config'
+import { getSystemConfig, invalidateSystemConfig } from '../lib/config'
 import { reset401Flag, httpClient } from '../lib/httpClient'
 import { getPostAuthPath, setUserMode, type UserMode } from '../lib/onboarding'
 import { useLanguage } from './LanguageContext'
@@ -225,6 +225,10 @@ export function AuthProvider({ children }: { children: React.ReactNode }) {
       }>('/api/register', requestBody)
 
       if (result.success && result.data) {
+        // Clear stale onboarding state so new users always see the welcome flow
+        localStorage.removeItem('nofx_beginner_onboarding_completed')
+        localStorage.removeItem('nofx_beginner_wallet_address')
+
         const userInfo = { id: result.data.user_id, email: result.data.email }
         handlePostAuthSuccess(result.data.token, userInfo, mode)
 
@@ -290,6 +294,7 @@ export function AuthProvider({ children }: { children: React.ReactNode }) {
     setToken(null)
     localStorage.removeItem('auth_token')
     localStorage.removeItem('auth_user')
+    invalidateSystemConfig()
     window.history.pushState({}, '', '/')
     window.dispatchEvent(new PopStateEvent('popstate'))
   }