fix(language): drop motion from VIEW_DEPENDENT_STYLES

Motion primitives are described in robot-frame (joint / Cartesian) terms,
not pixel space, so they are camera-agnostic. Only `vqa` (event) and
`trace` (event, pixel-trajectory) are view-dependent.

The `camera` field stays on PERSISTENT_ROW_FIELDS for schema symmetry —
the validator, resolver, and HF feature mapping behave identically across
the two columns regardless of which styles populate `camera` today —
but persistent rows now always have `camera=None` in practice.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lerobot/datasets/language.py

@@ -36,8 +36,15 @@ EVENT_ONLY_STYLES = {"interjection", "vqa", "trace"}
 
 # Styles whose ``content`` is grounded in a specific camera view. Rows of these
 # styles MUST carry a non-null ``camera`` referencing an ``observation.images.*``
-# feature key. Rows of every other style MUST have ``camera=None``.
-VIEW_DEPENDENT_STYLES = {"vqa", "motion", "trace"}
+# feature key. Rows of every other style MUST have ``camera=None``. ``motion``
+# is intentionally NOT in this set: motion primitives are described in
+# robot-frame (joint / Cartesian) terms, not pixel space, so they are
+# camera-agnostic. ``trace`` is the pixel-trajectory event style and IS
+# view-dependent. The ``camera`` field nevertheless lives on
+# ``PERSISTENT_ROW_FIELDS`` too so the schema, validator, and resolver
+# behave symmetrically across the two columns; persistent rows simply
+# always have ``camera=None`` in practice today.
+VIEW_DEPENDENT_STYLES = {"vqa", "trace"}
 
 LanguageColumn = Literal["language_persistent", "language_events"]
 

tests/datasets/test_language.py

@@ -58,10 +58,13 @@ def test_style_registry_routes_columns():
 
 
 def test_view_dependent_styles():
-    assert {"vqa", "motion", "trace"} == VIEW_DEPENDENT_STYLES
+    # motion lives in PERSISTENT_STYLES and is described in robot-frame
+    # (joint / Cartesian) terms, so it is NOT view-dependent. Only vqa
+    # (event) and trace (event, pixel-trajectory) carry a camera tag.
+    assert {"vqa", "trace"} == VIEW_DEPENDENT_STYLES
     assert is_view_dependent_style("vqa")
-    assert is_view_dependent_style("motion")
     assert is_view_dependent_style("trace")
+    assert not is_view_dependent_style("motion")
     assert not is_view_dependent_style("subtask")
     assert not is_view_dependent_style("plan")
     assert not is_view_dependent_style("interjection")
@@ -70,22 +73,24 @@ def test_view_dependent_styles():
 
 def test_validate_camera_field_requires_camera_for_view_dependent_styles():
     validate_camera_field("vqa", "observation.images.top")
-    validate_camera_field("motion", "observation.images.wrist")
     validate_camera_field("trace", "observation.images.front")
     with pytest.raises(ValueError, match="view-dependent"):
         validate_camera_field("vqa", None)
     with pytest.raises(ValueError, match="view-dependent"):
-        validate_camera_field("motion", "")
+        validate_camera_field("trace", "")
 
 
 def test_validate_camera_field_rejects_camera_on_non_view_dependent_styles():
     validate_camera_field("subtask", None)
     validate_camera_field("plan", None)
     validate_camera_field("memory", None)
+    validate_camera_field("motion", None)
     validate_camera_field("interjection", None)
     validate_camera_field(None, None)
     with pytest.raises(ValueError, match="must have camera=None"):
         validate_camera_field("subtask", "observation.images.top")
+    with pytest.raises(ValueError, match="must have camera=None"):
+        validate_camera_field("motion", "observation.images.top")
     with pytest.raises(ValueError, match="must have camera=None"):
         validate_camera_field("interjection", "observation.images.top")
     with pytest.raises(ValueError, match="must have camera=None"):