fix file system cat prefix determination

backend/src/lib/outbound/file_system.rs

@@ -626,6 +626,15 @@ impl PathRequest {
             }
         }
 
+        let lowest_common_prefix = if let Some(last_slash_index) = lowest_common_prefix.rfind("/")
+            && last_slash_index > 1
+        {
+            lowest_common_prefix.truncate(last_slash_index);
+            lowest_common_prefix
+        } else {
+            lowest_common_prefix
+        };
+
         Ok(Self::Multiple {
             lowest_common_prefix,
             paths: input_paths,