fix(validation): use activity 3350 and detect server outage

Cookie validation improvements:
1. Validate with activity ID 3350 (more reliable test endpoint)
2. Distinguish 5xx (outage) from 4xx (invalid cookie) during validation
3. On 5xx during validation: preserve cookie, don't re-login (server outage)
4. On 401/403 during validation: clear cookie and re-login
5. On network error during validation: preserve cookie (treat as server issue)

This prevents unnecessary re-logins during server outages.

engage-api/get-activity.ts

@@ -185,10 +185,36 @@ export async function fetchActivityData(
   if (shouldValidateCookieOnNextRequest) {
     logger.info('Validating cookie after previous server error...');
     shouldValidateCookieOnNextRequest = false;
-    // Simple validation: try to fetch a known activity
-    const testResponse = await getActivityDetailsRaw('1', currentCookie, 1, 5000);
+    // Simple validation: try to fetch a known activity (ID 3350)
+    const testResponse = await getActivityDetailsRaw('3350', currentCookie, 1, 5000);
     if (!testResponse) {
-      logger.warn('Cookie validation failed after server error. Re-login required.');
+      // Check if this is still a server error (5xx) - if so, it's an outage, don't re-login
+      // Just preserve existing cookie and return null
+      logger.warn('Cookie validation returned null. Checking if server is still down...');
+      
+      // Try one more time with explicit status check
+      try {
+        const url = 'https://engage.nkcswx.cn/Services/ActivitiesService.asmx/GetActivityDetails';
+        const headers = {
+          'Content-Type': 'application/json; charset=UTF-8',
+          'Cookie': currentCookie,
+          'User-Agent': 'Mozilla/5.0 (Bun DSAS-CCA Cookie Validator)',
+          'X-Requested-With': 'XMLHttpRequest'
+        };
+        const payload = { "activityID": "3350" };
+        const validationResponse = await axios.post(url, payload, {
+          headers,
+          timeout: 5000,
+          responseType: 'text'
+        });
+        
+        if (validationResponse.status >= 500 && validationResponse.status < 600) {
+          // Server still returning 5xx - it's an outage, preserve cookie and don't re-login
+          logger.warn('Server still returning 5xx during validation - treating as server outage, preserving cookie.');
+          return null;
+        } else if (validationResponse.status === 401 || validationResponse.status === 403) {
+          // Cookie is invalid, re-login
+          logger.warn('Cookie validation failed with 4xx. Re-login required.');
           await clearCookieCache();
           try {
             currentCookie = await getCompleteCookies(userName, userPwd);
@@ -201,6 +227,20 @@ export async function fetchActivityData(
             logger.error(`Re-login failed: ${(loginError as Error).message}`);
             return null;
           }
+        } else {
+          // Some other error, preserve cookie
+          logger.warn('Cookie validation failed with unexpected status. Preserving existing cookie.');
+          return null;
+        }
+      } catch (validationError: any) {
+        // Network error or timeout during validation - treat as server issue, preserve cookie
+        if (validationError.response && validationError.response.status >= 500) {
+          logger.warn('Server error during cookie validation - treating as outage, preserving cookie.');
+        } else {
+          logger.warn(`Network error during cookie validation: ${validationError.message}. Preserving existing cookie.`);
+        }
+        return null;
+      }
     } else {
       logger.info('Cookie validation successful after server error.');
     }