fix(datasets): Resolve only recipe-referenced bindings

Eagerly resolving every DEFAULT_BINDINGS entry made rendering fail on
frames whose events a default binding cannot disambiguate, e.g. the
camera-less vqa default on multi-camera frames, even when the recipe
never references that binding. Add TrainingRecipe.referenced_binding_names()
and skip bindings the recipe does not consume.

Split out of #4183 so the data-layer fix lands independently of the
language runtime.

Refs #4183
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/lerobot/configs/recipe.py

@@ -192,6 +192,13 @@ class TrainingRecipe:
             if recipe.weight <= 0:
                 raise ValueError(f"Blend component {name!r} must have a positive weight.")
 
+    def referenced_binding_names(self) -> set[str]:
+        """Names of every binding referenced by this recipe's message turns."""
+        names: set[str] = set()
+        for turn in self.messages or []:
+            names |= self._referenced_bindings(turn)
+        return names
+
     def _referenced_bindings(self, turn: MessageTurn) -> set[str]:
         """Return the binding names that ``turn`` references via placeholders or attributes."""
         names: set[str] = set()

src/lerobot/datasets/language_render.py

@@ -290,8 +290,14 @@ def _resolve_bindings(
     bindings: dict[str, LanguageRow | str | None] = {
         "task": _resolve_task(task, dataset_ctx, persistent=persistent, sample_idx=sample_idx),
     }
-    specs = {**DEFAULT_BINDINGS, **(recipe.bindings or {})}
+    declared = recipe.bindings or {}
+    specs = {**DEFAULT_BINDINGS, **declared}
+    # Only resolve bindings the recipe consumes: an unreferenced default may be
+    # unresolvable, e.g. the camera-less ``vqa`` default on multi-camera frames.
+    needed = recipe.referenced_binding_names() | set(declared)
     for name, spec in specs.items():
+        if name not in needed:
+            continue
         bindings[name] = _resolve_spec(spec, persistent=persistent, events=events, t=t)
     return bindings
 

tests/datasets/test_language_render.py

@@ -197,6 +197,34 @@ def test_emitted_at_filters_vqa_by_camera():
     assert wrist["content"] == '{"count": 1}'
 
 
+def test_unreferenced_default_bindings_are_not_resolved():
+    # A recipe that never references ``vqa`` must render on frames carrying
+    # multi-camera VQA events, which the camera-less default ``vqa`` binding
+    # cannot disambiguate (regression: eager DEFAULT_BINDINGS resolution).
+    recipe = TrainingRecipe(
+        messages=[
+            MessageTurn(role="user", content="${task}", stream="low_level"),
+            MessageTurn(
+                role="assistant",
+                content="${subtask}",
+                stream="low_level",
+                target=True,
+                if_present="subtask",
+            ),
+        ]
+    )
+    rendered = render_sample(
+        recipe=recipe,
+        persistent=PERSISTENT,
+        events=EVENTS_AT_3_TWO_CAMERAS,
+        t=3.0,
+        sample_idx=0,
+        task="tidy the table",
+    )
+    assert rendered is not None
+    assert rendered["messages"][1]["content"] == "subtask 1"
+
+
 def test_emitted_at_raises_on_ambiguous_per_camera_vqa():
     with pytest.raises(ValueError, match="Ambiguous resolver"):
         emitted_at(