feat: 添加对手动执行步骤 4 的前置条件检查，确保认证页标签存在

background/message-router.js

@@ -40,6 +40,7 @@
       getPendingAutoRunTimerPlan,
       getSourceLabel,
       getState,
+      getTabId,
       getStopRequested,
       handleAutoRunLoopUnhandledError,
       importSettingsBundle,
@@ -50,6 +51,7 @@
       isLocalhostOAuthCallbackUrl,
       isLuckmailProvider,
       isStopError,
+      isTabAlive,
       launchAutoRunTimerPlan,
       listIcloudAliases,
       listLuckmailPurchasesForManagement,
@@ -108,6 +110,23 @@
       return appendAccountRunRecord(status, state, reason);
     }
 
+    async function ensureManualStepPrerequisites(step) {
+      if (step !== 4) {
+        return;
+      }
+
+      const signupTabId = typeof getTabId === 'function'
+        ? await getTabId('signup-page')
+        : null;
+      const signupTabAlive = signupTabId && typeof isTabAlive === 'function'
+        ? await isTabAlive('signup-page')
+        : Boolean(signupTabId);
+
+      if (!signupTabId || !signupTabAlive) {
+        throw new Error('手动执行步骤 4 前，请先执行步骤 1 或步骤 2，确保认证页仍然打开并停留在验证码页。');
+      }
+    }
+
     async function handleStepData(step, payload) {
       switch (step) {
         case 1: {
@@ -402,6 +421,9 @@
             await ensureManualInteractionAllowed('手动执行步骤');
           }
           const step = message.payload.step;
+          if (message.source === 'sidepanel') {
+            await ensureManualStepPrerequisites(step);
+          }
           if (message.source === 'sidepanel') {
             await invalidateDownstreamAfterStepRestart(step, { logLabel: `步骤 ${step} 重新执行` });
           }

background/steps/fetch-signup-code.js

@@ -72,7 +72,7 @@
       const signupTabId = await getTabId('signup-page');
 
       if (!signupTabId) {
-        throw new Error('认证页面标签页已关闭，无法继续步骤 4。');
+        throw new Error('认证页面标签页已关闭，无法继续步骤 4。请先执行步骤 1 或步骤 2，重新打开认证页后再试。');
       }
 
       await chrome.tabs.update(signupTabId, { active: true });