fix

internal/client/client.go

@@ -134,9 +134,11 @@ func (c *Client) streamToS3(snapshot *zfs.Dataset, uploadURL, storageKey string)
 		gzWriter := gzip.NewWriter(pw)
 
 		go func() {
-			defer pw.Close()
-			defer gzWriter.Close()
+			// Copy zfs output to gzip writer
 			io.Copy(gzWriter, zfsOut)
+			// Close gzip writer first to flush footer, then close pipe
+			gzWriter.Close()
+			pw.Close()
 		}()
 
 		reader = pr