feat(grok): 对齐 free-usage/empty 失败分类与 sticky/ReAuth 体验

从 grokcli 吸收 body-first 失败分类（free-usage/empty/billing），
接到现有 temp_unsched 与 failover，保留 content-policy 与 pool_mode。
Grok 粘连/缓存在无显式 session 时可用 previous_response_id；
ReAuth 预填 email---- 并默认密码 tab（密码不落库）。

frontend/src/components/admin/account/ReAuthAccountModal.vue

@@ -137,6 +137,8 @@
         :method-label="t('admin.accounts.inputMethod')"
         :platform="isOpenAI ? 'openai' : isGemini ? 'gemini' : isAntigravity ? 'antigravity' : isGrok ? 'grok' : 'anthropic'"
         :show-project-id="isGemini && geminiOAuthType === 'code_assist'"
+        :initial-input-method="grokInitialInputMethod"
+        :initial-email-password="grokPrefillEmailPassword"
         @generate-url="handleGenerateUrl"
         @cookie-auth="handleCookieAuth"
         @validate-refresh-token="handleGrokValidateRefreshToken"
@@ -255,6 +257,40 @@ const isAnthropic = computed(() => props.account?.platform === 'anthropic')
 const isAntigravity = computed(() => props.account?.platform === 'antigravity')
 const isGrok = computed(() => props.account?.platform === 'grok')
 
+/** Stored Grok email for reauth prefill (password is never stored). */
+const grokAccountEmail = computed(() => {
+  if (!isGrok.value || !props.account) return ''
+  const creds = (props.account.credentials || {}) as Record<string, unknown>
+  const email = typeof creds.email === 'string' ? creds.email.trim() : ''
+  return email
+})
+
+/**
+ * Prefill "email----" so the operator only types the password.
+ * Empty when no email is known (full email----password required).
+ */
+const grokPrefillEmailPassword = computed(() => {
+  const email = grokAccountEmail.value
+  return email ? `${email}----` : ''
+})
+
+/**
+ * Grok reauth default tab:
+ * - password first when we know the email (common reauth path)
+ * - refresh_token when email unknown but RT may still work
+ * - email_password otherwise
+ */
+const grokInitialInputMethod = computed<AuthInputMethod>(() => {
+  if (!isGrok.value) return 'manual'
+  if (grokAccountEmail.value) return 'email_password'
+  const creds = (props.account?.credentials || {}) as Record<string, unknown>
+  const hasRT =
+    (typeof creds.refresh_token === 'string' && creds.refresh_token.trim() !== '') ||
+    (typeof creds.has_refresh_token === 'boolean' && creds.has_refresh_token)
+  if (hasRT) return 'refresh_token'
+  return 'email_password'
+})
+
 // Computed - current OAuth state based on platform
 const currentAuthUrl = computed(() => {
   if (isOpenAILike.value) return openaiOAuth.authUrl.value

frontend/src/components/admin/account/__tests__/ReAuthAccountModal.grok.spec.ts

@@ -32,4 +32,13 @@ describe('ReAuthAccountModal Grok re-auth paths', () => {
     expect(source).toContain("method === 'email_password'")
     expect(source).toContain("method === 'refresh_token'")
   })
+
+  it('prefills email---- and defaults to password method when email is known', () => {
+    expect(source).toContain('grokPrefillEmailPassword')
+    expect(source).toContain('grokInitialInputMethod')
+    expect(source).toContain(':initial-email-password="grokPrefillEmailPassword"')
+    expect(source).toContain(':initial-input-method="grokInitialInputMethod"')
+    expect(source).toContain('email----')
+    expect(source).toContain("return 'email_password'")
+  })
 })