fix: clarify wechat existing account binding

frontend/src/views/auth/WechatCallbackView.vue

@@ -116,11 +116,16 @@
                     {{ t('auth.alreadyHaveAccount') }}
                   </p>
                   <p class="text-xs text-gray-500 dark:text-dark-400">
-                    Sign in to an existing account, then bind this WeChat identity to it.
+                    {{
+                      hasCurrentAuthToken
+                        ? 'Bind this WeChat identity to the account currently signed in on this browser.'
+                        : 'Sign in to an existing account, then bind this WeChat identity to it.'
+                    }}
                   </p>
                 </div>
 
                 <input
+                  v-if="!hasCurrentAuthToken"
                   v-model="existingAccountEmail"
                   data-testid="existing-account-email"
                   type="email"
@@ -136,7 +141,7 @@
                   :disabled="isSubmitting"
                   @click="handleExistingAccountBinding"
                 >
-                  {{ t('auth.signIn') }}
+                  {{ hasCurrentAuthToken ? 'Bind current account' : t('auth.signIn') }}
                 </button>
               </div>
             </div>
@@ -353,6 +358,7 @@ const bindSuccessMessage = t('profile.authBindings.bindSuccess')
 const providerName = 'WeChat'
 const needsCreateAccount = computed(() => pendingAccountAction.value === 'create_account')
 const needsBindLogin = computed(() => pendingAccountAction.value === 'bind_login')
+const hasCurrentAuthToken = computed(() => Boolean(getAuthToken()))
 
 type PendingWeChatCompletion = PendingOAuthExchangeResponse & {
   step?: string

frontend/src/views/auth/__tests__/WechatCallbackView.spec.ts

@@ -345,6 +345,35 @@ describe('WechatCallbackView', () => {
     expect(replaceMock.mock.calls[0]?.[0]).toContain('mode%3Dopen')
   })
 
+  it('binds directly to the current signed-in account during invitation flow', async () => {
+    exchangePendingOAuthCompletionMock.mockResolvedValue({
+      error: 'invitation_required',
+      redirect: '/usage',
+    })
+    getAuthTokenMock.mockReturnValue('current-auth-token')
+
+    const wrapper = mount(WechatCallbackView, {
+      global: {
+        stubs: {
+          AuthLayout: { template: '<div><slot /></div>' },
+          Icon: true,
+          RouterLink: { template: '<a><slot /></a>' },
+          transition: false,
+        },
+      },
+    })
+
+    await flushPromises()
+
+    expect(wrapper.find('[data-testid="existing-account-email"]').exists()).toBe(false)
+    await wrapper.get('[data-testid="existing-account-submit"]').trigger('click')
+
+    expect(prepareOAuthBindAccessTokenCookieMock).toHaveBeenCalledTimes(1)
+    expect(locationState.current.href).toContain('intent=bind_current_user')
+    expect(locationState.current.href).toContain('redirect=%2Fusage')
+    expect(locationState.current.href).toContain('mode=open')
+  })
+
   it('collects email for pending oauth account creation and submits adoption decisions', async () => {
     exchangePendingOAuthCompletionMock.mockResolvedValue({
       error: 'email_required',