fix(robot): type FK-to-EE action features as ACTION not STATE (#4213)

* fix(robot): type FK-to-EE action features as ACTION not STATE

ForwardKinematicsJointsToEEAction.transform_features declared its
end-effector action features (ee.x/y/z/wx/wy/wz/gripper_pos) with
FeatureType.STATE, copied verbatim from the sibling
ForwardKinematicsJointsToEEObservation (where STATE is correct for
OBSERVATION features). Every other action-producing step in this file
(EEReferenceAndDelta, InverseKinematicsEEToJoints, InverseKinematicsRLStep)
types its ACTION-bucket features as FeatureType.ACTION.

The mismatch mis-classifies the converted EE actions as state, which
propagates a wrong feature schema to downstream consumers keyed on
FeatureType (e.g. normalization norm_map, policy input/output feature
classification).


* test(robot): FK-to-EE step feature-type contract (action vs observation)

Asserts ForwardKinematicsJointsToEEAction emits EE features in the ACTION
bucket typed FeatureType.ACTION, and ForwardKinematicsJointsToEEObservation
emits them in the OBSERVATION bucket typed FeatureType.STATE.


* chore: delete user file

* chore(processor): reduce verbosity

---------

Co-authored-by: Jaagat-P <jaagatp05@gmail.com>

src/lerobot/robots/so_follower/robot_kinematic_processor.py

@@ -510,10 +510,10 @@ class ForwardKinematicsJointsToEEAction(RobotActionProcessorStep):
         # We only use the ee pose in the dataset, so we don't need the joint positions
         for n in self.motor_names:
             features[PipelineFeatureType.ACTION].pop(f"{n}.pos", None)
-        # We specify the dataset features of this step that we want to be stored in the dataset
+        # Store end-effector features as actions in the dataset schema
         for k in ["x", "y", "z", "wx", "wy", "wz", "gripper_pos"]:
             features[PipelineFeatureType.ACTION][f"ee.{k}"] = PolicyFeature(
-                type=FeatureType.STATE, shape=(1,)
+                type=FeatureType.ACTION, shape=(1,)
             )
         return features
 

tests/robots/test_robot_kinematic_processor.py

@@ -0,0 +1,45 @@
+#!/usr/bin/env python
+
+# Copyright 2025 The HuggingFace Inc. team. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import pytest
+
+from lerobot.configs import FeatureType, PipelineFeatureType, PolicyFeature
+from lerobot.robots.so_follower.robot_kinematic_processor import (
+    ForwardKinematicsJointsToEEAction,
+    ForwardKinematicsJointsToEEObservation,
+)
+
+MOTOR_NAMES = ["shoulder_pan", "shoulder_lift", "elbow_flex", "wrist_flex", "wrist_roll", "gripper"]
+EE_KEYS = {f"ee.{k}" for k in ["x", "y", "z", "wx", "wy", "wz", "gripper_pos"]}
+
+
+def _joint_bucket(feature_type: FeatureType) -> dict[str, PolicyFeature]:
+    return {f"{n}.pos": PolicyFeature(type=feature_type, shape=(1,)) for n in MOTOR_NAMES}
+
+
+@pytest.mark.parametrize(
+    ("step_cls", "bucket", "feature_type"),
+    [
+        (ForwardKinematicsJointsToEEAction, PipelineFeatureType.ACTION, FeatureType.ACTION),
+        (ForwardKinematicsJointsToEEObservation, PipelineFeatureType.OBSERVATION, FeatureType.STATE),
+    ],
+)
+def test_fk_feature_schema(step_cls, bucket, feature_type):
+    features = {PipelineFeatureType.ACTION: {}, PipelineFeatureType.OBSERVATION: {}}
+    features[bucket] = _joint_bucket(feature_type)
+    out = step_cls(kinematics=None, motor_names=MOTOR_NAMES).transform_features(features)[bucket]
+    assert set(out) == EE_KEYS
+    assert {feature.type for feature in out.values()} == {feature_type}