diff --git a/src/accounting-app/app.ts b/src/accounting-app/app.ts
index 704dbab..eb20adf 100644
--- a/src/accounting-app/app.ts
+++ b/src/accounting-app/app.ts
@@ -15,26 +15,7 @@ import App from './App.vue'
 import '@/assets/index.css'
 import { i18n, changeLocale, type AvailableLocale } from '@/i18n'
 import { installStrictAuthGuard, markAuthReady, catchAllRoute } from '@/lib/router-helpers'
-
-/**
- * Accept an auth token from a URL parameter (e.g. ?token=xxx).
- * This allows the main app to link users directly into Castle
- * without requiring a separate login. The token is stored in
- * localStorage and the parameter is stripped from the URL.
- */
-function acceptTokenFromUrl() {
-  const params = new URLSearchParams(window.location.search)
-  const token = params.get('token')
-  if (token) {
-    localStorage.setItem('lnbits_access_token', token)
-    // Also persist user data key so auth service picks it up
-    params.delete('token')
-    const clean = params.toString()
-    const newUrl = window.location.pathname + (clean ? `?${clean}` : '') + window.location.hash
-    window.history.replaceState({}, '', newUrl)
-    console.log('[Castle] Auth token accepted from URL')
-  }
-}
+import { acceptTokenFromUrl } from '@/lib/url-token'
 
 /**
  * Initialize the standalone Castle accounting app
@@ -43,7 +24,7 @@ export async function createAppInstance() {
   console.log('Starting Castle — Accounting App...')
 
   // Accept token from URL before anything else (cross-subdomain auth relay)
-  acceptTokenFromUrl()
+  acceptTokenFromUrl('Castle')
 
   const app = createApp(App)
 
diff --git a/src/activities-app/app.ts b/src/activities-app/app.ts
index e2bc818..581a6e2 100644
--- a/src/activities-app/app.ts
+++ b/src/activities-app/app.ts
@@ -14,24 +14,7 @@ import App from './App.vue'
 import '@/assets/index.css'
 import { i18n, changeLocale, type AvailableLocale } from '@/i18n'
 import { installLenientAuthGuard, markAuthReady, catchAllRoute } from '@/lib/router-helpers'
-
-/**
- * Accept an auth token from a URL parameter (e.g. ?token=xxx).
- * Allows the main app to link users directly into this standalone
- * app without requiring a separate login.
- */
-function acceptTokenFromUrl() {
-  const params = new URLSearchParams(window.location.search)
-  const token = params.get('token')
-  if (token) {
-    localStorage.setItem('lnbits_access_token', token)
-    params.delete('token')
-    const clean = params.toString()
-    const newUrl = window.location.pathname + (clean ? `?${clean}` : '') + window.location.hash
-    window.history.replaceState({}, '', newUrl)
-    console.log('[Sortir] Auth token accepted from URL')
-  }
-}
+import { acceptTokenFromUrl } from '@/lib/url-token'
 
 /**
  * Initialize the standalone activities app
@@ -40,7 +23,7 @@ export async function createAppInstance() {
   console.log('🚀 Starting Sortir — Activities App...')
 
   // Accept token from URL before anything else (cross-subdomain auth relay)
-  acceptTokenFromUrl()
+  acceptTokenFromUrl('Sortir')
 
   const app = createApp(App)
 
diff --git a/src/chat-app/app.ts b/src/chat-app/app.ts
index f107399..d4b2573 100644
--- a/src/chat-app/app.ts
+++ b/src/chat-app/app.ts
@@ -14,24 +14,12 @@ import App from './App.vue'
 import '@/assets/index.css'
 import { i18n, changeLocale, type AvailableLocale } from '@/i18n'
 import { installStrictAuthGuard, markAuthReady, catchAllRoute } from '@/lib/router-helpers'
-
-function acceptTokenFromUrl() {
-  const params = new URLSearchParams(window.location.search)
-  const token = params.get('token')
-  if (token) {
-    localStorage.setItem('lnbits_access_token', token)
-    params.delete('token')
-    const clean = params.toString()
-    const newUrl = window.location.pathname + (clean ? `?${clean}` : '') + window.location.hash
-    window.history.replaceState({}, '', newUrl)
-    console.log('[Chat] Auth token accepted from URL')
-  }
-}
+import { acceptTokenFromUrl } from '@/lib/url-token'
 
 export async function createAppInstance() {
   console.log('Starting Chat app...')
 
-  acceptTokenFromUrl()
+  acceptTokenFromUrl('Chat')
 
   const app = createApp(App)
 
diff --git a/src/forum-app/app.ts b/src/forum-app/app.ts
index 66d6d19..b1e1d4c 100644
--- a/src/forum-app/app.ts
+++ b/src/forum-app/app.ts
@@ -14,24 +14,12 @@ import App from './App.vue'
 import '@/assets/index.css'
 import { i18n, changeLocale, type AvailableLocale } from '@/i18n'
 import { installLenientAuthGuard, markAuthReady, catchAllRoute } from '@/lib/router-helpers'
-
-function acceptTokenFromUrl() {
-  const params = new URLSearchParams(window.location.search)
-  const token = params.get('token')
-  if (token) {
-    localStorage.setItem('lnbits_access_token', token)
-    params.delete('token')
-    const clean = params.toString()
-    const newUrl = window.location.pathname + (clean ? `?${clean}` : '') + window.location.hash
-    window.history.replaceState({}, '', newUrl)
-    console.log('[Forum] Auth token accepted from URL')
-  }
-}
+import { acceptTokenFromUrl } from '@/lib/url-token'
 
 export async function createAppInstance() {
   console.log('Starting Forum app...')
 
-  acceptTokenFromUrl()
+  acceptTokenFromUrl('Forum')
 
   const app = createApp(App)
 
diff --git a/src/lib/api/lnbits.ts b/src/lib/api/lnbits.ts
index 1166cc8..c837861 100644
--- a/src/lib/api/lnbits.ts
+++ b/src/lib/api/lnbits.ts
@@ -195,6 +195,35 @@ export class LnbitsAPI extends BaseService {
     return !!this.accessToken
   }
 
+  /**
+   * Server-validate a token and adopt it if valid (issue #36).
+   *
+   * Called by AuthService.checkAuth() when a pending URL-supplied token is
+   * found in localStorage. We can't trust the token until the server has
+   * confirmed it represents a real session, so:
+   *   1. Temporarily set the candidate token on the API client
+   *   2. Try getCurrentUser() with it
+   *   3. On success → persist to AUTH_TOKEN_KEY, return the user
+   *   4. On failure → restore the previous token (if any), return null
+   *
+   * The pending token is the caller's responsibility to remove from
+   * localStorage afterwards.
+   */
+  async tryAdoptToken(candidateToken: string): Promise<User | null> {
+    const previousToken = this.accessToken
+    this.accessToken = candidateToken
+    try {
+      const user = await this.getCurrentUser()
+      // Server confirmed — persist for future page loads
+      setAuthToken(candidateToken)
+      return user
+    } catch (err) {
+      console.warn('[LnbitsAPI] Pending URL token rejected by server:', err)
+      this.accessToken = previousToken
+      return null
+    }
+  }
+
   getAccessToken(): string | null {
     return this.accessToken
   }
diff --git a/src/lib/config/lnbits.ts b/src/lib/config/lnbits.ts
index 5d6ce0c..dec6c8e 100644
--- a/src/lib/config/lnbits.ts
+++ b/src/lib/config/lnbits.ts
@@ -13,6 +13,11 @@ export const LNBITS_CONFIG = {
   // Auth token storage key
   AUTH_TOKEN_KEY: 'lnbits_access_token',
 
+  // Transient key for tokens received via ?token=… URL params. They live here
+  // until validateAndAdoptPendingToken() server-checks them; only validated
+  // tokens get promoted to AUTH_TOKEN_KEY. See issue #36.
+  PENDING_AUTH_TOKEN_KEY: 'lnbits_pending_token',
+
   // User storage key
   USER_STORAGE_KEY: 'lnbits_user_data'
 }
@@ -42,4 +47,20 @@ export function setAuthToken(token: string): void {
 // Helper function to remove auth token from storage
 export function removeAuthToken(): void {
   localStorage.removeItem(LNBITS_CONFIG.AUTH_TOKEN_KEY)
-} 
+}
+
+// Pending token (URL-supplied, unvalidated) helpers.
+// Pending tokens land here from acceptTokenFromUrl() and only get promoted
+// to the real AUTH_TOKEN_KEY after server validation.
+export function getPendingAuthToken(): string | null {
+  return localStorage.getItem(LNBITS_CONFIG.PENDING_AUTH_TOKEN_KEY)
+}
+
+export function setPendingAuthToken(token: string): void {
+  localStorage.setItem(LNBITS_CONFIG.PENDING_AUTH_TOKEN_KEY, token)
+}
+
+export function removePendingAuthToken(): void {
+  localStorage.removeItem(LNBITS_CONFIG.PENDING_AUTH_TOKEN_KEY)
+}
+
diff --git a/src/lib/router-helpers.ts b/src/lib/router-helpers.ts
index b0cac33..c23bf9d 100644
--- a/src/lib/router-helpers.ts
+++ b/src/lib/router-helpers.ts
@@ -14,7 +14,14 @@ import type { Router, RouteRecordRaw } from 'vue-router'
  * mismatch: guards register early but await this promise before reading
  * auth state. Phase 3 calls markAuthReady() once auth is initialized.
  */
-type AuthLike = { isAuthenticated: { value: boolean } }
+type AuthUserLike = { value: { pubkey?: string } | null }
+type AuthLike = {
+  isAuthenticated: { value: boolean }
+  // Populated after server-validated getCurrentUser() in auth.checkAuth().
+  // Guards require BOTH isAuthenticated and a user with a pubkey — token
+  // presence alone is not enough (issue #36).
+  currentUser: AuthUserLike
+}
 
 let resolveAuth!: (a: AuthLike) => void
 const authReady: Promise<AuthLike> = new Promise(r => { resolveAuth = r })
@@ -23,6 +30,15 @@ export function markAuthReady(auth: AuthLike): void {
   resolveAuth(auth)
 }
 
+/**
+ * Belt-and-suspenders auth check: token presence in localStorage isn't
+ * sufficient — the server must have confirmed the token represents a real
+ * session, which is signalled by currentUser being populated with a pubkey.
+ */
+function isFullyAuthed(auth: AuthLike): boolean {
+  return auth.isAuthenticated.value && !!auth.currentUser?.value?.pubkey
+}
+
 /**
  * Strict guard — every non-/login route requires auth.
  * Used by wallet, chat, castle (no public view).
@@ -30,10 +46,11 @@ export function markAuthReady(auth: AuthLike): void {
 export function installStrictAuthGuard(router: Router): void {
   router.beforeEach(async (to) => {
     const auth = await authReady
+    const authed = isFullyAuthed(auth)
     if (to.path === '/login') {
-      return auth.isAuthenticated.value ? '/' : true
+      return authed ? '/' : true
     }
-    return auth.isAuthenticated.value ? true : '/login'
+    return authed ? true : '/login'
   })
 }
 
@@ -45,8 +62,9 @@ export function installLenientAuthGuard(router: Router): void {
   router.beforeEach(async (to) => {
     const auth = await authReady
     const requiresAuth = to.meta.requiresAuth === true
-    if (requiresAuth && !auth.isAuthenticated.value) return '/login'
-    if (to.path === '/login' && auth.isAuthenticated.value) return '/'
+    const authed = isFullyAuthed(auth)
+    if (requiresAuth && !authed) return '/login'
+    if (to.path === '/login' && authed) return '/'
     return true
   })
 }
diff --git a/src/lib/url-token.ts b/src/lib/url-token.ts
new file mode 100644
index 0000000..01ee5a8
--- /dev/null
+++ b/src/lib/url-token.ts
@@ -0,0 +1,27 @@
+import { setPendingAuthToken } from '@/lib/config/lnbits'
+
+/**
+ * Cross-subdomain auth relay (issue #36): pull `?token=…` off the URL into
+ * the pending-token slot in localStorage, then strip it from history so it
+ * doesn't bleed into bookmarks or referrers.
+ *
+ * The token is NOT promoted to the real auth-token slot here. AuthService
+ * .checkAuth() server-validates it via lnbitsAPI.tryAdoptToken() and only
+ * persists it if the LNbits backend confirms it represents a real session.
+ *
+ * Call this synchronously at app boot, before createApp(), so the URL is
+ * cleaned before vue-router has a chance to read it. The pending token sits
+ * in localStorage until auth.initialize() picks it up later in the same
+ * page load.
+ */
+export function acceptTokenFromUrl(appName: string): void {
+  const params = new URLSearchParams(window.location.search)
+  const token = params.get('token')
+  if (!token) return
+  setPendingAuthToken(token)
+  params.delete('token')
+  const clean = params.toString()
+  const newUrl = window.location.pathname + (clean ? `?${clean}` : '') + window.location.hash
+  window.history.replaceState({}, '', newUrl)
+  console.log(`[${appName}] URL token captured for server validation`)
+}
diff --git a/src/market-app/app.ts b/src/market-app/app.ts
index 9b7e936..103ce53 100644
--- a/src/market-app/app.ts
+++ b/src/market-app/app.ts
@@ -14,24 +14,12 @@ import App from './App.vue'
 import '@/assets/index.css'
 import { i18n, changeLocale, type AvailableLocale } from '@/i18n'
 import { installLenientAuthGuard, markAuthReady, catchAllRoute } from '@/lib/router-helpers'
-
-function acceptTokenFromUrl() {
-  const params = new URLSearchParams(window.location.search)
-  const token = params.get('token')
-  if (token) {
-    localStorage.setItem('lnbits_access_token', token)
-    params.delete('token')
-    const clean = params.toString()
-    const newUrl = window.location.pathname + (clean ? `?${clean}` : '') + window.location.hash
-    window.history.replaceState({}, '', newUrl)
-    console.log('[Market] Auth token accepted from URL')
-  }
-}
+import { acceptTokenFromUrl } from '@/lib/url-token'
 
 export async function createAppInstance() {
   console.log('Starting Market app...')
 
-  acceptTokenFromUrl()
+  acceptTokenFromUrl('Market')
 
   const app = createApp(App)
 
diff --git a/src/modules/base/auth/auth-service.ts b/src/modules/base/auth/auth-service.ts
index 9f64931..7b4b6fe 100644
--- a/src/modules/base/auth/auth-service.ts
+++ b/src/modules/base/auth/auth-service.ts
@@ -5,6 +5,7 @@ import { eventBus } from '@/core/event-bus'
 import { injectService, SERVICE_TOKENS } from '@/core/di-container'
 import type { LoginCredentials, RegisterData, User } from '@/lib/api/lnbits'
 import type { NostrMetadataService } from '../nostr/nostr-metadata-service'
+import { getPendingAuthToken, removePendingAuthToken } from '@/lib/config/lnbits'
 
 export class AuthService extends BaseService {
   // Service metadata
@@ -49,6 +50,28 @@ export class AuthService extends BaseService {
   }
 
   async checkAuth(): Promise<boolean> {
+    // Pending URL-supplied token (from acceptTokenFromUrl in app shells).
+    // Validate server-side before promoting to the real auth-token slot —
+    // see issue #36. Always remove the pending entry whether validation
+    // succeeds or fails so it can't recur on later boots.
+    const pending = getPendingAuthToken()
+    if (pending) {
+      removePendingAuthToken()
+      this.isLoading.value = true
+      try {
+        const adopted = await this.lnbitsAPI.tryAdoptToken(pending)
+        if (adopted) {
+          this.user.value = adopted
+          this.isAuthenticated.value = true
+          this.debug(`Adopted pending URL token for ${adopted.username || adopted.id}`)
+          return true
+        }
+        this.debug('Pending URL token rejected — falling through to existing token')
+      } finally {
+        this.isLoading.value = false
+      }
+    }
+
     if (!this.lnbitsAPI.isAuthenticated()) {
       this.debug('No auth token found - user needs to login')
       this.isAuthenticated.value = false
@@ -59,14 +82,14 @@ export class AuthService extends BaseService {
     try {
       this.isLoading.value = true
       const userData = await this.lnbitsAPI.getCurrentUser()
-      
+
       this.user.value = userData
       this.isAuthenticated.value = true
-      
+
       this.debug(`User authenticated: ${userData.username || userData.id} (${userData.pubkey?.slice(0, 8)})`)
-      
+
       return true
-      
+
     } catch (error) {
       this.handleError(error, 'checkAuth')
       this.isAuthenticated.value = false
diff --git a/src/modules/market/views/MarketDashboard.vue b/src/modules/market/views/MarketDashboard.vue
index 44aac34..ded7018 100644
--- a/src/modules/market/views/MarketDashboard.vue
+++ b/src/modules/market/views/MarketDashboard.vue
@@ -62,7 +62,7 @@
 
 <script setup lang="ts">
 import { ref, computed, onMounted } from 'vue'
-import { useRoute } from 'vue-router'
+import { useRoute, useRouter } from 'vue-router'
 import { useMarketStore } from '@/modules/market/stores/market'
 import { Badge } from '@/components/ui/badge'
 import { 
@@ -138,8 +138,20 @@ const tabs = computed(() => [
   }
 ])
 
+const router = useRouter()
+
 // Lifecycle
 onMounted(() => {
+  // Defence-in-depth: the router guard should already have redirected an
+  // unauthenticated visitor, but if a regression slips past it (issue #36
+  // root cause), bounce here too. Auth is "real" only when both the token
+  // is present AND the server-validated user object has a pubkey.
+  const fullyAuthed = auth.isAuthenticated.value && !!auth.currentUser?.value?.pubkey
+  if (!fullyAuthed) {
+    console.warn('[MarketDashboard] Mounted without full auth — redirecting to /login')
+    router.replace('/login')
+    return
+  }
   console.log('Market Dashboard mounted')
 })
 </script>
diff --git a/src/tasks-app/app.ts b/src/tasks-app/app.ts
index 25fce53..2223842 100644
--- a/src/tasks-app/app.ts
+++ b/src/tasks-app/app.ts
@@ -14,24 +14,12 @@ import App from './App.vue'
 import '@/assets/index.css'
 import { i18n, changeLocale, type AvailableLocale } from '@/i18n'
 import { installLenientAuthGuard, markAuthReady, catchAllRoute } from '@/lib/router-helpers'
-
-function acceptTokenFromUrl() {
-  const params = new URLSearchParams(window.location.search)
-  const token = params.get('token')
-  if (token) {
-    localStorage.setItem('lnbits_access_token', token)
-    params.delete('token')
-    const clean = params.toString()
-    const newUrl = window.location.pathname + (clean ? `?${clean}` : '') + window.location.hash
-    window.history.replaceState({}, '', newUrl)
-    console.log('[Tasks] Auth token accepted from URL')
-  }
-}
+import { acceptTokenFromUrl } from '@/lib/url-token'
 
 export async function createAppInstance() {
   console.log('Starting Tasks app...')
 
-  acceptTokenFromUrl()
+  acceptTokenFromUrl('Tasks')
 
   const app = createApp(App)
 
diff --git a/src/wallet-app/app.ts b/src/wallet-app/app.ts
index 07d1cef..e9fc6ae 100644
--- a/src/wallet-app/app.ts
+++ b/src/wallet-app/app.ts
@@ -14,28 +14,12 @@ import App from './App.vue'
 import '@/assets/index.css'
 import { i18n, changeLocale, type AvailableLocale } from '@/i18n'
 import { installStrictAuthGuard, markAuthReady, catchAllRoute } from '@/lib/router-helpers'
-
-/**
- * Accept an auth token from a URL parameter (e.g. ?token=xxx).
- * Allows the hub to link users into Wallet without re-login.
- */
-function acceptTokenFromUrl() {
-  const params = new URLSearchParams(window.location.search)
-  const token = params.get('token')
-  if (token) {
-    localStorage.setItem('lnbits_access_token', token)
-    params.delete('token')
-    const clean = params.toString()
-    const newUrl = window.location.pathname + (clean ? `?${clean}` : '') + window.location.hash
-    window.history.replaceState({}, '', newUrl)
-    console.log('[Wallet] Auth token accepted from URL')
-  }
-}
+import { acceptTokenFromUrl } from '@/lib/url-token'
 
 export async function createAppInstance() {
   console.log('Starting Wallet app...')
 
-  acceptTokenFromUrl()
+  acceptTokenFromUrl('Wallet')
 
   const app = createApp(App)