preserve detailed logs

Author: lizk886

src/main/java/com/uid2/shared/vertx/CloudSyncVerticle.java

@@ -400,8 +400,13 @@ private void cloudDownloadBlocking(String s3Path) throws Exception {
 
             downloadFailureTimer.record(java.time.Duration.ofMillis(cloudDownloadTimeMs));            
             // Be careful as the s3Path may contain the pre-signed S3 token, so do not log the whole path
-            LOGGER.error("download error: " + ex.getClass().getSimpleName());
-            throw new CloudStorageException("Download failed"); 
+            LOGGER.error("Cloud storage download error, exception type: " + ex.getClass().getSimpleName());
+            
+            if (ex instanceof CloudStorageException) {
+                throw (CloudStorageException) ex;
+            }
+            throw new CloudStorageException("Failed to download file from cloud storage, exception: " 
+                + ex.getClass().getSimpleName() + ", please check network connectivity and service availability"); 
         }
     }