Document preserved action fields

README.md

@@ -65,6 +65,26 @@ It was generated with `droid_filter.py` from `/scratch/jellyho/prsl_skills`.
 - Min/max episode length: `57` / `1044`
 - Episode success rate: `1.0`
 
+## Preserved Action Fields
+
+Filtering only selects episodes/rows. It does **not** drop action-space columns.
+The following action columns are preserved from the original DROID parquet files:
+
+```text
+action.gripper_position
+action.gripper_velocity
+action.cartesian_position
+action.cartesian_velocity
+action.joint_position
+action.joint_velocity
+action.original
+action
+```
+
+`action` is the compact 8D policy action used by LeRobot-style loaders. The
+additional `action.*` columns remain available in the parquet files for
+inspection or custom loaders.
+
 ## Top Tasks
 
 | task_text | episodes |