Merge branch 'main' into feat/language-columns

Reword the two callouts in `tools.mdx` to describe the runtime layer
in present tense ("not part of the catalog layer shipped today",
"those modules don't yet exist in the tree") instead of pointing at a
specific follow-up PR. Keeps the doc honest about what works now
without coupling it to a particular release order.

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

.github/workflows/release.yml

@@ -152,14 +152,13 @@ jobs:
             BASE_VERSION="${VERSION%%-*}"
             echo "Installing pre-release version $BASE_VERSION from TestPyPI..."
             uv pip install \
-              --torch-backend cpu \
               --index-url https://test.pypi.org/simple/ \
               --extra-index-url https://pypi.org/simple \
               --index-strategy unsafe-best-match \
                "lerobot[all]==$BASE_VERSION"
           else
             echo "Installing release version $VERSION from PyPI..."
-            uv pip install --torch-backend cpu "lerobot[all]==$VERSION"
+            uv pip install "lerobot[all]==$VERSION"
           fi
       - name: Check lerobot version
         run: uv run python -c "import lerobot; print(lerobot.__version__)"

.github/workflows/stale.yml

@@ -19,8 +19,8 @@ on:
   workflow_dispatch:
 
   # Runs at 02:00
-  # schedule:
-  #   - cron: "0 2 * * *"
+  schedule:
+    - cron: "0 2 * * *"
 
 env:
   CLOSE_ISSUE_MESSAGE: >

AGENT_GUIDE.md

@@ -232,8 +232,6 @@ Match the policy to the user's **GPU memory** and **time budget**. Numbers below
 
 All policies typically train for **5–10 epochs** (see §7).
 
-> **Human-facing version:** the [Compute Hardware Guide](./docs/source/hardware_guide.mdx) reuses the table below and adds a cloud-GPU tier guide and a Hugging Face Jobs pointer.
-
 | Policy      | Batch | Update (ms) | Peak GPU mem (GB) | Best for                                                                                         |
 | ----------- | ----: | ----------: | ----------------: | ------------------------------------------------------------------------------------------------ |
 | `act`       |     4 |    **83.9** |          **0.94** | First-time users, laptops, single-task. Fast and reliable.                                       |

README.md

@@ -109,7 +109,7 @@ lerobot-train \
 
 Similarly to the hardware, you can easily implement your own policy & leverage LeRobot's data collection, training, and visualization tools, and share your model to the HF Hub
 
-For detailed policy setup guides, see the [Policy Documentation](https://huggingface.co/docs/lerobot/bring_your_own_policies). For GPU/RAM requirements and expected training time per policy, see the [Compute Hardware Guide](https://huggingface.co/docs/lerobot/hardware_guide).
+For detailed policy setup guides, see the [Policy Documentation](https://huggingface.co/docs/lerobot/bring_your_own_policies).
 
 ## Inference & Evaluation
 

docker/Dockerfile.benchmark.robotwin

@@ -35,7 +35,7 @@ USER root
 ARG ROBOTWIN_SHA=0aeea2d669c0f8516f4d5785f0aa33ba812c14b4
 RUN apt-get update \
     && apt-get install -y --no-install-recommends \
-         cuda-nvcc-12-8 cuda-cudart-dev-12-8 \
+         cuda-nvcc-12-6 cuda-cudart-dev-12-6 \
          libvulkan1 vulkan-tools \
     && mkdir -p /usr/share/vulkan/icd.d \
     && echo '{"file_format_version":"1.0.0","ICD":{"library_path":"libGLX_nvidia.so.0","api_version":"1.3.0"}}' \

docker/Dockerfile.internal

@@ -18,7 +18,7 @@
 # docker build -f docker/Dockerfile.internal -t lerobot-internal .
 
 # Configure the base image for CI with GPU access
-ARG CUDA_VERSION=12.8.1
+ARG CUDA_VERSION=12.6.3
 ARG OS_VERSION=24.04
 FROM nvidia/cuda:${CUDA_VERSION}-base-ubuntu${OS_VERSION}
 

docs/source/_toctree.yml

@@ -3,14 +3,12 @@
     title: LeRobot
   - local: installation
     title: Installation
-  - local: cheat-sheet
-    title: Cheat sheet
   title: Get started
 - sections:
   - local: il_robots
     title: Imitation Learning for Robots
   - local: bring_your_own_policies
-    title: Adding a Policy
+    title: Bring Your Own Policies
   - local: integrate_hardware
     title: Bring Your Own Hardware
   - local: hilserl
@@ -26,12 +24,6 @@
   - local: rename_map
     title: Using Rename Map and Empty Cameras
   title: "Tutorials"
-- sections:
-  - local: hardware_guide
-    title: Compute Hardware Guide
-  - local: torch_accelerators
-    title: PyTorch accelerators
-  title: "Compute & Hardware"
 - sections:
   - local: lerobot-dataset-v3
     title: Using LeRobotDataset
@@ -39,8 +31,10 @@
     title: Porting Large Datasets
   - local: using_dataset_tools
     title: Using the Dataset Tools
-  - local: dataset_subtask
-    title: Using Subtasks in the Dataset
+  - local: language_and_recipes
+    title: Language Columns and Recipes
+  - local: tools
+    title: Tools
   - local: streaming_video_encoding
     title: Streaming Video Encoding
   title: "Datasets"
@@ -150,6 +144,10 @@
   - local: cameras
     title: Cameras
   title: "Sensors"
+- sections:
+  - local: torch_accelerators
+    title: PyTorch accelerators
+  title: "Supported Hardware"
 - sections:
   - local: notebooks
     title: Notebooks

docs/source/bring_your_own_policies.mdx

@@ -1,37 +1,60 @@
-# Adding a Policy
+# Bring Your Own Policies
 
-This guide walks you through implementing a custom policy and getting it to work with LeRobot's training, evaluation, and deployment tools. There are two paths:
+This tutorial explains how to integrate your own custom policy implementations into the LeRobot ecosystem, allowing you to leverage all LeRobot tools for training, evaluation, and deployment while using your own algorithms.
 
-- **Plugin (out-of-tree)** — ship your policy as a standalone `lerobot_policy_*` package. Faster, no PR required, easy to iterate. Right for experimentation, internal use, or when you want to publish independently.
-- **In-tree (contributed to LeRobot)** — land your policy directly in `src/lerobot/policies/`. Requires a PR, but makes your policy a first-class citizen of the library.
+## Step 1: Create a Policy Package
 
-The plugin route is usually the right starting point — promote to in-tree once the policy has stabilized and there's clear value in shipping it with the library.
+Your custom policy should be organized as an installable Python package following LeRobot's plugin conventions.
 
-Either way, the building blocks are the same: a configuration class, a policy class, and a processor factory. The first half of this guide covers those shared pieces; the second half covers the path-specific scaffolding ([Path A](#path-a-out-of-tree-plugin), [Path B](#path-b-contributing-in-tree)).
+### Package Structure
 
-A note on tone: robot-learning is an actively evolving field, and "what a policy looks like" can shift with each new architecture. The conventions described here exist because they let `lerobot-train` and `lerobot-eval` work uniformly across very different models. When a new policy genuinely doesn't fit them, raise it (in your PR, or an issue) — the conventions are not sacred.
+Create a package with the prefix `lerobot_policy_` (IMPORTANT!) followed by your policy name:
 
----
+```bash
+lerobot_policy_my_custom_policy/
+├── pyproject.toml
+└── src/
+    └── lerobot_policy_my_custom_policy/
+        ├── __init__.py
+        ├── configuration_my_custom_policy.py
+        ├── modeling_my_custom_policy.py
+        └── processor_my_custom_policy.py
+```
 
-## Anatomy of a policy
+### Package Configuration
 
-Three building blocks make up every policy. The names below use `my_policy` as a placeholder — replace with your policy's name. That name is load-bearing: it must match the string you pass to `@PreTrainedConfig.register_subclass`, the `MyPolicy.name` class attribute, and the `make_<name>_pre_post_processors` factory function (more on each below).
+Set up your `pyproject.toml`:
 
-### Configuration class
+```toml
+[project]
+name = "lerobot_policy_my_custom_policy"
+version = "0.1.0"
+dependencies = [
+    # your policy-specific dependencies
+]
+requires-python = ">= 3.12"
 
-Inherit from [`PreTrainedConfig`](https://github.com/huggingface/lerobot/blob/main/src/lerobot/configs/policies.py) and register your policy type. Here is a template — customize the parameters and methods as needed for your policy's architecture and training requirements.
+[build-system]
+build-backend = # your-build-backend
+requires = # your-build-system
+```
+
+## Step 2: Define the Policy Configuration
+
+Create a configuration class that inherits from [`PreTrainedConfig`](https://github.com/huggingface/lerobot/blob/main/src/lerobot/configs/policies.py) and registers your policy type:
+Here is a template to get you started, customize the parameters and methods as needed for your policy's architecture and training requirements.
 
 ```python
-# configuration_my_policy.py
+# configuration_my_custom_policy.py
 from dataclasses import dataclass, field
 from lerobot.configs import PreTrainedConfig
 from lerobot.optim import AdamWConfig
 from lerobot.optim import CosineDecayWithWarmupSchedulerConfig
 
-@PreTrainedConfig.register_subclass("my_policy")
+@PreTrainedConfig.register_subclass("my_custom_policy")
 @dataclass
-class MyPolicyConfig(PreTrainedConfig):
-    """Configuration class for MyPolicy.
+class MyCustomPolicyConfig(PreTrainedConfig):
+    """Configuration class for MyCustomPolicy.
 
     Args:
         n_obs_steps: Number of observation steps to use as input
@@ -54,20 +77,16 @@ class MyPolicyConfig(PreTrainedConfig):
             raise ValueError("n_action_steps cannot exceed horizon")
 
     def validate_features(self) -> None:
-        """Validate input/output feature compatibility.
-
-        Call this explicitly from your policy's __init__ — the base class does not.
-        """
+        """Validate input/output feature compatibility."""
         if not self.image_features:
-            raise ValueError("MyPolicy requires at least one image feature.")
+            raise ValueError("MyCustomPolicy requires at least one image feature.")
         if self.action_feature is None:
-            raise ValueError("MyPolicy requires 'action' in output_features.")
+            raise ValueError("MyCustomPolicy requires 'action' in output_features.")
 
     def get_optimizer_preset(self) -> AdamWConfig:
         return AdamWConfig(lr=self.optimizer_lr, weight_decay=self.optimizer_weight_decay)
 
     def get_scheduler_preset(self):
-        """Return a LRSchedulerConfig from lerobot.optim, or None."""
         return None
 
     @property
@@ -82,7 +101,8 @@ class MyPolicyConfig(PreTrainedConfig):
 
     @property
     def action_delta_indices(self) -> list[int]:
-        """Relative timestep offsets for the action chunk the dataset loader returns."""
+        """Relative timestep offsets for the action chunk the dataset loader returns.
+        """
         return list(range(self.horizon))
 
     @property
@@ -90,34 +110,32 @@ class MyPolicyConfig(PreTrainedConfig):
         return None
 ```
 
-The string you pass to `@register_subclass` must match `MyPolicy.name` (next section) and is what users supply as `--policy.type` on the CLI. Default to `AdamW` from `lerobot.optim` for `get_optimizer_preset` unless you genuinely need otherwise.
+## Step 3: Implement the Policy Class
 
-### Policy class
-
-Inherit from [`PreTrainedPolicy`](https://github.com/huggingface/lerobot/blob/main/src/lerobot/policies/pretrained.py) and set two class attributes — both are checked by `__init_subclass__`:
+Create your policy implementation by inheriting from [`PreTrainedPolicy`](https://github.com/huggingface/lerobot/blob/main/src/lerobot/policies/pretrained.py):
 
 ```python
-# modeling_my_policy.py
+# modeling_my_custom_policy.py
 import torch
 import torch.nn as nn
 from typing import Any
 
 from lerobot.policies import PreTrainedPolicy
 from lerobot.utils.constants import ACTION
-from .configuration_my_policy import MyPolicyConfig
+from .configuration_my_custom_policy import MyCustomPolicyConfig
 
-class MyPolicy(PreTrainedPolicy):
-    config_class = MyPolicyConfig  # must match the string in @register_subclass
-    name = "my_policy"
+class MyCustomPolicy(PreTrainedPolicy):
+    config_class = MyCustomPolicyConfig  # must match the string in @register_subclass
+    name = "my_custom_policy"
 
-    def __init__(self, config: MyPolicyConfig, dataset_stats: dict[str, Any] = None):
+    def __init__(self, config: MyCustomPolicyConfig, dataset_stats: dict[str, Any] = None):
         super().__init__(config, dataset_stats)
         config.validate_features()  # not called automatically by the base class
         self.config = config
         self.model = ...  # your nn.Module here
 
     def reset(self):
-        """Reset per-episode state. Called by lerobot-eval at the start of each episode."""
+        """Reset episode state."""
         ...
 
     def get_optim_params(self) -> dict:
@@ -129,51 +147,35 @@ class MyPolicy(PreTrainedPolicy):
         ...
 
     def select_action(self, batch: dict[str, torch.Tensor], **kwargs) -> torch.Tensor:
-        """Return a single action for the current timestep (called every step at inference)."""
+        """Return a single action for the current timestep (called at inference)."""
         ...
 
-    def forward(self, batch: dict[str, torch.Tensor]) -> tuple[torch.Tensor, dict | None]:
+    def forward(self, batch: dict[str, torch.Tensor]) -> dict[str, torch.Tensor]:
         """Compute the training loss.
 
-        Returns `(loss, output_dict)`. `output_dict` may be `None`; everything in it must be
-        logging-friendly Python natives (no tensors with gradients).
-
         `batch["action_is_pad"]` is a bool mask of shape (B, horizon) that marks
-        timesteps padded because the episode ended before `horizon` steps; you
+        timesteps padded because the episode ended before `horizon` steps, you
         can exclude those from your loss.
         """
         actions = batch[ACTION]
         action_is_pad = batch.get("action_is_pad")
         ...
-        return loss, {"some_loss_component": some_loss_component.item()}
+        return {"loss": ...}
 ```
 
-The methods called by the train/eval loops:
+## Step 4: Add Data Processors
 
-| Method                                                            | Used by           | What it does                                                                                                                                                                                                                                         |
-| ----------------------------------------------------------------- | ----------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
-| `reset() -> None`                                                 | `lerobot-eval`    | Clear per-episode state at the start of each episode.                                                                                                                                                                                                |
-| `select_action(batch, **kwargs) -> Tensor`                        | `lerobot-eval`    | Return the next action `(B, action_dim)`. Called every step.                                                                                                                                                                                         |
-| `predict_action_chunk(batch, **kwargs) -> Tensor`                 | the policy itself | Return an action chunk `(B, chunk_size, action_dim)`. Currently abstract on the base class — raise `NotImplementedError` if your policy doesn't chunk.                                                                                               |
-| `forward(batch, reduction="mean") -> tuple[Tensor, dict \| None]` | `lerobot-train`   | Return `(loss, output_dict)`. Accept `reduction="none"` if you want to support per-sample weighting.                                                                                                                                                 |
-| `get_optim_params() -> dict`                                      | the optimizer     | Return `self.parameters()` for simple policies; return a named parameter dict for [multi-optimizer policies](https://github.com/huggingface/lerobot/blob/ecd38c50d7d15b4184cf42649ff1185ee2e11eeb/src/lerobot/policies/sac/modeling_sac.py#L61-L73). |
-| `update() -> None` _(optional)_                                   | `lerobot-train`   | Called after each optimizer step _if defined_. Use for EMA, target nets, replay buffers (TDMPC uses this).                                                                                                                                           |
-
-Batches are flat dictionaries keyed by the constants in [`lerobot.utils.constants`](https://github.com/huggingface/lerobot/blob/main/src/lerobot/utils/constants.py): `OBS_STATE` (`observation.state.<motor>`), `OBS_IMAGES` (`observation.images.<camera>`), `OBS_LANGUAGE`, `ACTION`, etc. Reuse the constants — don't invent new prefixes.
-
-### Processor functions
-
-LeRobot uses `PolicyProcessorPipeline`s to normalize inputs and de-normalize outputs around your policy. For a concrete reference, see [`processor_act.py`](https://github.com/huggingface/lerobot/blob/main/src/lerobot/policies/act/processor_act.py) or [`processor_diffusion.py`](https://github.com/huggingface/lerobot/blob/main/src/lerobot/policies/diffusion/processor_diffusion.py).
+Create processor functions. For a concrete reference, see [processor_act.py](https://github.com/huggingface/lerobot/blob/main/src/lerobot/policies/act/processor_act.py) or [processor_diffusion.py](https://github.com/huggingface/lerobot/blob/main/src/lerobot/policies/diffusion/processor_diffusion.py).
 
 ```python
-# processor_my_policy.py
+# processor_my_custom_policy.py
 from typing import Any
 import torch
 
 from lerobot.processor import PolicyAction, PolicyProcessorPipeline
 
 
-def make_my_policy_pre_post_processors(
+def make_my_custom_policy_pre_post_processors(
     config,
     dataset_stats: dict[str, dict[str, torch.Tensor]] | None = None,
 ) -> tuple[
@@ -185,48 +187,11 @@ def make_my_policy_pre_post_processors(
     return preprocessor, postprocessor
 ```
 
-**Important — function naming:** LeRobot discovers your processor by name. The function **must** be called `make_{policy_name}_pre_post_processors` (matching the string you passed to `@PreTrainedConfig.register_subclass`).
+**Important - function naming:** LeRobot discovers your processor by name. The function **must** be called `make_{policy_name}_pre_post_processors` (matching the string you passed to `@PreTrainedConfig.register_subclass`).
 
----
+## Step 5: Package Initialization
 
-## Path A: Out-of-tree plugin
-
-The fastest way to ship a policy: package it as a standalone Python distribution and install it alongside LeRobot. No PR required, you own the release cycle, and you can publish to PyPI under your own namespace.
-
-### Package structure
-
-Create a package with the prefix `lerobot_policy_` (IMPORTANT!) followed by your policy name:
-
-```bash
-lerobot_policy_my_policy/
-├── pyproject.toml
-└── src/
-    └── lerobot_policy_my_policy/
-        ├── __init__.py
-        ├── configuration_my_policy.py
-        ├── modeling_my_policy.py
-        └── processor_my_policy.py
-```
-
-### `pyproject.toml`
-
-```toml
-[project]
-name = "lerobot_policy_my_policy"
-version = "0.1.0"
-dependencies = [
-    # your policy-specific dependencies
-]
-requires-python = ">= 3.12"
-
-[build-system]
-build-backend = # your-build-backend
-requires = # your-build-system
-```
-
-### Package `__init__.py`
-
-Expose your classes in the package's `__init__.py` and guard against missing `lerobot`:
+Expose your classes in the package's `__init__.py`:
 
 ```python
 # __init__.py
@@ -239,148 +204,44 @@ except ImportError:
         "lerobot is not installed. Please install lerobot to use this policy package."
     )
 
-from .configuration_my_policy import MyPolicyConfig
-from .modeling_my_policy import MyPolicy
-from .processor_my_policy import make_my_policy_pre_post_processors
+from .configuration_my_custom_policy import MyCustomPolicyConfig
+from .modeling_my_custom_policy import MyCustomPolicy
+from .processor_my_custom_policy import make_my_custom_policy_pre_post_processors
 
 __all__ = [
-    "MyPolicyConfig",
-    "MyPolicy",
-    "make_my_policy_pre_post_processors",
+    "MyCustomPolicyConfig",
+    "MyCustomPolicy",
+    "make_my_custom_policy_pre_post_processors",
 ]
 ```
 
-### Install and use
+## Step 6: Installation and Usage
+
+### Install Your Policy Package
 
 ```bash
-cd lerobot_policy_my_policy
+cd lerobot_policy_my_custom_policy
 pip install -e .
 
 # Or install from PyPI if published
-pip install lerobot_policy_my_policy
+pip install lerobot_policy_my_custom_policy
 ```
 
+### Use Your Policy
+
 Once installed, your policy automatically integrates with LeRobot's training and evaluation tools:
 
 ```bash
 lerobot-train \
-    --policy.type my_policy \
+    --policy.type my_custom_policy \
     --env.type pusht \
     --steps 200000
 ```
 
----
-
-## Path B: Contributing in-tree
-
-When your policy has stabilized and there's clear value in shipping it with the library, you can land it directly in LeRobot. Read the general [contribution guide](./contributing) and the [PR template](https://github.com/huggingface/lerobot/blob/main/.github/PULL_REQUEST_TEMPLATE.md) first — that's where you'll find the testing/quality expectations every PR has to meet (`pre-commit run -a`, `pytest`, the community-review rule, etc.). What's below is the policy-specific layer on top of that.
-
-### In-tree layout
-
-```
-src/lerobot/policies/my_policy/
-├── __init__.py                    # re-exports config + modeling + processor factory
-├── configuration_my_policy.py     # MyPolicyConfig + @register_subclass
-├── modeling_my_policy.py          # MyPolicy(PreTrainedPolicy)
-├── processor_my_policy.py         # make_my_policy_pre_post_processors
-└── README.md                      # symlink → ../../../../docs/source/policy_my_policy_README.md
-```
-
-Two notes:
-
-- The `README.md` next to the source is a **symlink** into `docs/source/policy_<name>_README.md` — the actual file lives under `docs/`. Existing policies (act, smolvla, diffusion, …) all do this; copy one of those symlinks. The policy README is conventionally minimal: paper link + BibTeX citation.
-- The user-facing tutorial — what to install, how to train, hyperparameters, benchmark numbers — lives separately at `docs/source/<my_policy>.mdx` and is registered in `_toctree.yml` under "Policies".
-
-The file names are load-bearing: the factory does lazy imports by name, and the processor is discovered by the `make_<policy_name>_pre_post_processors` convention.
-
-### Wiring
-
-Three places need to know about your policy. All by name.
-
-1. **`policies/__init__.py`** — re-export `MyPolicyConfig` and add it to `__all__`. **Don't** re-export the modeling class; it loads lazily through the factory (so `import lerobot` stays fast).
-2. **`factory.py:get_policy_class`** — add a branch returning `MyPolicy` from a lazy import.
-3. **`factory.py:make_policy_config`** and **`factory.py:make_pre_post_processors`** — same idea, two more branches.
-
-Mirror an existing policy that's structurally similar to yours; the diff is small.
-
-### Heavy / optional dependencies
-
-Most policies need a heavy backbone (transformers, diffusers, a specific VLM SDK). The convention is **two-step gating**: a `TYPE_CHECKING`-guarded import at module top, and a `require_package` runtime check in the constructor. [`modeling_diffusion.py`](https://github.com/huggingface/lerobot/blob/main/src/lerobot/policies/diffusion/modeling_diffusion.py) is the canonical reference:
-
-```python
-from typing import TYPE_CHECKING
-from lerobot.utils.import_utils import _diffusers_available, require_package
-
-if TYPE_CHECKING or _diffusers_available:
-    from diffusers.schedulers.scheduling_ddim import DDIMScheduler
-else:
-    DDIMScheduler = None  # keeps the symbol bindable at import time
-
-class DiffusionPolicy(PreTrainedPolicy):
-    def __init__(self, config):
-        require_package("diffusers", extra="diffusion")
-        super().__init__(config)
-        ...
-```
-
-This way:
-
-- `import lerobot.policies` keeps working without the extra installed (the symbol is just bound to `None`).
-- Type checkers see the real symbol.
-- Instantiating the policy without the extra raises a clear `ImportError` pointing at `pip install 'lerobot[diffusion]'`.
-
-Add a matching extra to [`pyproject.toml`](https://github.com/huggingface/lerobot/blob/main/pyproject.toml) `[project.optional-dependencies]` and include it in the `all` extra so `pip install 'lerobot[all]'` keeps installing everything.
-
-### Benchmarks and a published checkpoint
-
-A new policy is much easier to review — and far more useful — when it ships with a working checkpoint and at least one number you can reproduce.
-
-**Pick at least one in-tree benchmark.** LeRobot ships sim benchmarks with per-benchmark Docker images (LIBERO, LIBERO-plus, Meta-World, RoboTwin 2.0, RoboCasa365, RoboCerebra, RoboMME, VLABench and more). Pick the one that matches your policy's modality — VLAs usually go to LIBERO or VLABench; image-only BC to LIBERO or Meta-World. The full list lives under [Benchmarks](./libero) in the docs sidebar.
-
-**Push the checkpoint & processors** to the Hub under `lerobot/<policy>_<benchmark>` (or your namespace if you don't have write access; a maintainer can mirror it). Use `PreTrainedPolicy.push_model_to_hub` so the repo gets `config.json`, `model.safetensors`, and a model card.
-
-**Report results in your policy's MDX**, with the exact `lerobot-eval` command and hardware so anyone can re-run:
-
-```markdown
-## Results
-
-Evaluated on LIBERO with `lerobot/<policy>_libero`:
-
-| Suite          | Success rate | n_episodes |
-| -------------- | -----------: | ---------: |
-| libero_spatial |        87.5% |         50 |
-| libero_object  |        93.0% |         50 |
-| libero_goal    |        81.5% |         50 |
-| libero_10      |        62.0% |         50 |
-| **average**    |    **81.0%** |        200 |
-
-Reproduce: `lerobot-eval --policy.path=lerobot/<policy>_libero --env.type=libero --env.task=libero_spatial --eval.n_episodes=50` (1× A100 40 GB).
-```
-
-Use `n_episodes ≥ 50` per suite for stable success-rate estimates.
-
-If your policy is real-robot-only and no sim benchmark applies, swap the sim eval for: a public training dataset on the Hub, the `lerobot-train` command, the checkpoint, and a real-robot success rate over ≥10 episodes via `lerobot-rollout --policy.path=...`.
-
-### PR checklist
-
-The general expectations are in [`CONTRIBUTING.md`](https://github.com/huggingface/lerobot/blob/main/CONTRIBUTING.md) and the [PR template](https://github.com/huggingface/lerobot/blob/main/.github/PULL_REQUEST_TEMPLATE.md). On top of those, reviewers will look for:
-
-- [ ] `MyPolicy` and `MyPolicyConfig` cover the surface above; `__init_subclass__` accepts the class.
-- [ ] `factory.py` and `policies/__init__.py` are wired (lazy imports for modeling).
-- [ ] `make_my_policy_pre_post_processors` follows the naming convention.
-- [ ] Optional deps live behind a `[project.optional-dependencies]` extra and the `TYPE_CHECKING + require_package` guard.
-- [ ] `tests/policies/` updated; backward-compat artifact committed & policy-specific tests.
-- [ ] `src/lerobot/policies/<name>/README.md` symlinked into `docs/source/policy_<name>_README.md`; user-facing `docs/source/<name>.mdx` written and added to `_toctree.yml`.
-- [ ] At least one reproducible benchmark eval in the policy MDX with a published checkpoint (sim benchmark, or real-robot dataset + checkpoint).
-
-The fastest way to get a clean PR is to copy the directory of the existing policy closest to yours, rename, and replace contents method by method. Don't wait until everything is polished — open a draft PR early and iterate with us; reviewers would much rather give feedback on a half-finished branch than a fully-merged one.
-
----
-
-## Examples and community contributions
+## Examples and Community Contributions
 
 Check out these example policy implementations:
 
-- [DiTFlow Policy](https://github.com/danielsanjosepro/lerobot_policy_ditflow) — Diffusion Transformer policy with flow-matching objective. Try it out in this example: [DiTFlow Example](https://github.com/danielsanjosepro/test_lerobot_policy_ditflow)
+- [DiTFlow Policy](https://github.com/danielsanjosepro/lerobot_policy_ditflow) - Diffusion Transformer policy with flow-matching objective. Try it out in this example: [DiTFlow Example](https://github.com/danielsanjosepro/test_lerobot_policy_ditflow)
 
-Thanks for taking the time to bring a new policy into LeRobot. Every architecture that lands in `main` — and every plugin published by the community — makes the library a little more useful for the next person, and a little more representative of where robot learning is going. We're looking forward to seeing what you ship. 🤗
+Share your policy implementations with the community! 🤗

docs/source/cheat-sheet.mdx

@@ -1,48 +0,0 @@
-# Cheat sheet
-All of the LeRobot commands in one place. If you forgot how to use a specific command or want to learn about a new one you can do it here.
-
-❗ For all of the commands listed below remember to change the ports/names/ids to your own values!
-
-> [!TIP]
-> Another grate way to look at all the comands and get them configured for your specific setup is to use this [Jupyter Notebook](https://github.com/huggingface/lerobot/blob/main/examples/notebooks/quickstart.ipynb).
-
-### Install
-
-### Useful tools
-###### Find port
-
-```bash
-lerobot-find-port
-```
-
-###### Find cameras
-```bash
-lerobot-find-cameras
-```
-
-### Calibration
-
-### Teleoperation
-
-### Recording a dataset
-
-### Training
-
-### Inference
-
-Inference means running the trained policy/model on a robot. For that we use ```lerobot-rollout```. You will need to provide a path to your policy. It can be a local path or a path to Hugging Face for example "lerobot/folding_latest". You cameras configuration need to match what was used when collecting the dataset. Duration is in seconds if unspecified it will run forever.
-
-> [!TIP]
-> If you are using the previous release V0.5.1 instead of ```lerobot-rollout``` you need to use ```lerobot-record```
-
-``` bash
-lerobot-rollout \
-  --strategy.type=base \
-  --policy.path=${HF_USER}/my_policy \
-  --robot.type=so101_follower \
-  --robot.port=/dev/ttyACM1 \
-  --robot.cameras="{ up: {type: opencv, index_or_path: /dev/video1, width: 640, height: 480, fps: 30}, side: {type: opencv, index_or_path: /dev/video5, width: 640, height: 480, fps: 30}}" \
-  --task="Put lego brick into the transparent box" \
-  --duration=60
-```
-

docs/source/dataset_subtask.mdx

@@ -1,277 +0,0 @@
-# Using Subtasks in LeRobot Datasets
-
-Subtask support in robotics datasets has proven effective in improving robot reasoning and understanding. Subtasks are particularly useful for:
-
-- **Hierarchical policies**: Building policies that include subtask predictions to visualize robot reasoning in real time
-- **Reward modeling**: Helping reward models understand task progression (e.g., SARM-style stage-aware reward models)
-- **Task decomposition**: Breaking down complex manipulation tasks into atomic, interpretable steps
-
-LeRobotDataset now supports subtasks as part of its dataset structure, alongside tasks.
-
-## What are Subtasks?
-
-While a **task** describes the overall goal (e.g., "Pick up the apple and place it in the basket"), **subtasks** break down the execution into finer-grained steps:
-
-1. "Approach the apple"
-2. "Grasp the apple"
-3. "Lift the apple"
-4. "Move to basket"
-5. "Release the apple"
-
-Each frame in the dataset can be annotated with its corresponding subtask, enabling models to learn and predict these intermediate stages.
-
-<img
-  src="https://huggingface.co/datasets/huggingface/documentation-images/resolve/main/lerobot/subtask-asset.png"
-  alt="An overview of subtask annotation showing how frames are labeled with intermediate subtask stages"
-  width="80%"
-/>
-
-<p>
-  <em>Figure: Overview of subtask annotation.</em>
-</p>
-
-**Reference:** _Subtask-learning based for robot self-assembly in flexible collaborative assembly in manufacturing_, Original Article, Published: 19 April 2022.
-
-## Dataset Structure
-
-Subtask information is stored in the dataset metadata:
-
-```
-my-dataset/
-├── data/
-│   └── ...
-├── meta/
-│   ├── info.json
-│   ├── stats.json
-│   ├── tasks.parquet
-│   ├── subtasks.parquet      # Subtask index → subtask string mapping
-│   └── episodes/
-│       └── ...
-└── videos/
-    └── ...
-```
-
-### Subtasks Parquet File
-
-The `meta/subtasks.parquet` file maps subtask indices to their natural language descriptions:
-
-| subtask_index | subtask (index column) |
-| ------------- | ---------------------- |
-| 0             | "Approach the apple"   |
-| 1             | "Grasp the apple"      |
-| 2             | "Lift the apple"       |
-| ...           | ...                    |
-
-### Frame-Level Annotations
-
-Each frame in the dataset can include a `subtask_index` field that references the subtasks parquet file:
-
-```python
-# Example frame data in the parquet file
-{
-    "index": 42,
-    "timestamp": 1.4,
-    "episode_index": 0,
-    "task_index": 0,
-    "subtask_index": 2,  # References "Lift the apple"
-    "observation.state": [...],
-    "action": [...],
-}
-```
-
-## Annotating Datasets with Subtasks
-
-We provide a HuggingFace Space for easily annotating any LeRobotDataset with subtasks:
-
-**[https://huggingface.co/spaces/lerobot/annotate](https://huggingface.co/spaces/lerobot/annotate)**
-
-After completing your annotation:
-
-1. Click "Push to Hub" to upload your annotated dataset
-2. You can also run the annotation space locally by following the instructions at [github.com/huggingface/lerobot-annotate](https://github.com/huggingface/lerobot-annotate)
-
-## Loading Datasets with Subtasks
-
-When you load a dataset with subtask annotations, the subtask information is automatically available:
-
-```python
-from lerobot.datasets import LeRobotDataset
-
-# Load a dataset with subtask annotations
-dataset = LeRobotDataset("jadechoghari/collect-fruit-annotated")
-
-# Access a sample
-sample = dataset[100]
-
-# The sample includes both task and subtask information
-print(sample["task"])        # "Collect the fruit"
-print(sample["subtask"])     # "Grasp the apple"
-print(sample["task_index"])  # tensor(0)
-print(sample["subtask_index"])  # tensor(2)
-```
-
-### Checking for Subtask Support
-
-You can check if a dataset has subtask annotations:
-
-```python
-# Check if subtasks are available
-has_subtasks = (
-    "subtask_index" in dataset.features
-    and dataset.meta.subtasks is not None
-)
-
-if has_subtasks:
-    print(f"Dataset has {len(dataset.meta.subtasks)} unique subtasks")
-    print("Subtasks:", list(dataset.meta.subtasks.index))
-```
-
-## Using Subtasks for Training
-
-### With the Tokenizer Processor
-
-The `TokenizerProcessor` automatically handles subtask tokenization for Vision-Language Action (VLA) models:
-
-```python
-from lerobot.processor import TokenizerProcessorStep
-
-# Create a tokenizer processor step
-tokenizer_processor = TokenizerProcessorStep(
-    tokenizer_name_or_path="google/paligemma-3b-pt-224",
-    padding="max_length",
-    max_length=64,
-)
-
-# The processor will automatically tokenize subtasks if present in the batch
-# and add them to the observation under:
-# - "observation.subtask.tokens"
-# - "observation.subtask.attention_mask"
-```
-
-When subtasks are available in the batch, the tokenizer processor adds:
-
-- `observation.subtask.tokens`: Tokenized subtask text
-- `observation.subtask.attention_mask`: Attention mask for the subtask tokens
-
-### DataLoader with Subtasks
-
-```python
-import torch
-from lerobot.datasets import LeRobotDataset
-
-dataset = LeRobotDataset("jadechoghari/collect-fruit-annotated")
-
-dataloader = torch.utils.data.DataLoader(
-    dataset,
-    batch_size=16,
-    shuffle=True,
-)
-
-for batch in dataloader:
-    # Access subtask information in the batch
-    subtasks = batch["subtask"]  # List of subtask strings
-    subtask_indices = batch["subtask_index"]  # Tensor of subtask indices
-
-    # Use for training hierarchical policies or reward models
-    print(f"Batch subtasks: {set(subtasks)}")
-```
-
-## Example Datasets with Subtask Annotations
-
-Try loading a dataset with subtask annotations:
-
-```python
-from lerobot.datasets import LeRobotDataset
-
-# Example dataset with subtask annotations
-dataset = LeRobotDataset("jadechoghari/collect-fruit-annotated")
-
-# Explore the subtasks
-print("Available subtasks:")
-for subtask_name in dataset.meta.subtasks.index:
-    print(f"  - {subtask_name}")
-
-# Get subtask distribution
-subtask_counts = {}
-for i in range(len(dataset)):
-    sample = dataset[i]
-    subtask = sample["subtask"]
-    subtask_counts[subtask] = subtask_counts.get(subtask, 0) + 1
-
-print("\nSubtask distribution:")
-for subtask, count in sorted(subtask_counts.items(), key=lambda x: -x[1]):
-    print(f"  {subtask}: {count} frames")
-```
-
-## Use Cases
-
-### 1. Hierarchical Policy Training
-
-Train policies that predict both actions and current subtask:
-
-```python
-class HierarchicalPolicy(nn.Module):
-    def __init__(self, num_subtasks):
-        super().__init__()
-        self.action_head = nn.Linear(hidden_dim, action_dim)
-        self.subtask_head = nn.Linear(hidden_dim, num_subtasks)
-
-    def forward(self, observations):
-        features = self.encoder(observations)
-        actions = self.action_head(features)
-        subtask_logits = self.subtask_head(features)
-        return actions, subtask_logits
-```
-
-### 2. Stage-Aware Reward Modeling (SARM)
-
-Build reward models that understand task progression:
-
-```python
-# SARM predicts:
-# - Stage: Which subtask is being executed (discrete)
-# - Progress: How far along the subtask (continuous 0-1)
-
-class SARMRewardModel(nn.Module):
-    def forward(self, observations):
-        features = self.encoder(observations)
-        stage_logits = self.stage_classifier(features)
-        progress = self.progress_regressor(features)
-        return stage_logits, progress
-```
-
-### 3. Progress Visualization
-
-Monitor robot execution by tracking subtask progression:
-
-```python
-def visualize_execution(model, observations):
-    for t, obs in enumerate(observations):
-        action, subtask_logits = model(obs)
-        predicted_subtask = subtask_names[subtask_logits.argmax()]
-        print(f"t={t}: Executing '{predicted_subtask}'")
-```
-
-## API Reference
-
-### LeRobotDataset Properties
-
-| Property                    | Type                   | Description                                |
-| --------------------------- | ---------------------- | ------------------------------------------ |
-| `meta.subtasks`             | `pd.DataFrame \| None` | DataFrame mapping subtask names to indices |
-| `features["subtask_index"]` | `dict`                 | Feature spec for subtask_index if present  |
-
-### Sample Keys
-
-When subtasks are available, each sample includes:
-
-| Key             | Type           | Description                          |
-| --------------- | -------------- | ------------------------------------ |
-| `subtask_index` | `torch.Tensor` | Integer index of the current subtask |
-| `subtask`       | `str`          | Natural language subtask description |
-
-## Related Resources
-
-- [SARM Paper](https://arxiv.org/pdf/2509.25358) - Stage-Aware Reward Modeling for Long Horizon Robot Manipulation
-- [LeRobot Annotate Space](https://huggingface.co/spaces/lerobot/annotate) - Interactive annotation tool
-- [LeRobotDataset v3.0](./lerobot-dataset-v3) - Dataset format documentation

docs/source/hardware_guide.mdx

@@ -1,98 +0,0 @@
-# Compute HW Guide for LeRobot Training
-
-Rough sizing for training a LeRobot policy: how much VRAM each policy needs, what training time looks like, and where to run when local hardware isn't enough.
-
-The numbers below are **indicative** — order-of-magnitude figures for picking hardware, not exact predictions. Throughput depends heavily on dataset I/O, image resolution, batch size, and number of GPUs.
-
-## Memory by policy group
-
-Policies cluster by backbone size; the groupings below give a single VRAM envelope per group instead of repeating numbers per policy. Memory scales roughly linearly with batch size; AdamW (the LeRobot default) carries optimizer state that adds ~30–100% over a forward+backward pass alone.
-
-| Group      | Policies                                    | Peak VRAM (BS 8, AdamW) | Suitable starter GPUs             |
-| ---------- | ------------------------------------------- | ----------------------: | --------------------------------- |
-| Light BC   | `act`, `vqbet`, `tdmpc`                     |                  ~2–6GB | Laptop GPU (RTX 3060), L4, A10G   |
-| Diffusion  | `diffusion`, `multi_task_dit`               |                 ~8–14GB | RTX 4070+ / L4 / A10G             |
-| Small VLA  | `smolvla`                                   |                ~10–16GB | RTX 4080+ / L4 / A10G             |
-| Large VLA  | `pi0`, `pi0_fast`, `pi05`, `xvla`, `wall_x` |                ~24–40GB | A100 40 GB+ (24 GB tight at BS 1) |
-| Multimodal | `groot`, `eo1`                              |                ~24–40GB | A100 40 GB+                       |
-| RL         | `sac`                                       |             config-dep. | See [HIL-SERL guide](./hilserl)   |
-
-Memory-bound? Drop the batch size (~linear), use gradient accumulation to recover effective batch, or for SmolVLA leave `freeze_vision_encoder=True`.
-
-## Training time
-
-Robotics imitation learning typically converges in **5–10 epochs over the dataset**, not hundreds of thousands of raw steps. Once you know your epoch count, wall-clock is essentially:
-
-```text
-total_frames    = sum of frames over all episodes      # 50 ep × 30 fps × 30 s ≈ 45,000
-steps_per_epoch = ceil(total_frames / (num_gpus × batch_size))
-total_steps     = epochs × steps_per_epoch
-wall_clock      ≈ total_steps × per_step_time
-```
-
-Per-step time depends on the policy and the GPU. The numbers in the table below are anchors — pick the row closest to your setup and scale linearly with `total_steps` if you train longer or shorter.
-
-### Common scenarios
-
-Indicative wall-clock for **5 epochs on a ~50-episode dataset (~45k frames at 30 fps × 30 s)**, default optimizer (AdamW), 640×480 images:
-
-| Setup                                | Policy         | Batch | Wall-clock |
-| ------------------------------------ | -------------- | ----- | ---------: |
-| Single RTX 4090 / RTX 3090 (24 GB)   | `act`          | 8     |  ~30–60min |
-| Single RTX 4090 / RTX 3090 (24 GB)   | `diffusion`    | 8     |      ~2–4h |
-| Single L4 / A10G (24 GB)             | `act`          | 8     |      ~1–2h |
-| Single L4 / A10G (24 GB)             | `smolvla`      | 4     |      ~3–6h |
-| Single A100 40 GB                    | `smolvla`      | 16    |      ~1–2h |
-| Single A100 40 GB                    | `pi0` / `pi05` | 4     |      ~4–8h |
-| 4× H100 80 GB cluster (`accelerate`) | `diffusion`    | 32    |  ~30–60min |
-| 4× H100 80 GB cluster (`accelerate`) | `smolvla`      | 32    |      ~1–2h |
-| Apple Silicon M1/M2/M3 Max (MPS)     | `act`          | 4     |     ~6–14h |
-
-These are order-of-magnitude figures. Real runs deviate by ±50% depending on image resolution, dataset I/O, dataloader threading, and exact GPU SKU. They are useful as "is this run going to take an hour or a day?" intuition, not as SLAs.
-
-### Multi-GPU matters a lot
-
-`accelerate launch --num_processes=N` is the easiest way to cut training time. Each optimizer step processes `N × batch_size` samples in roughly the same wall-clock as a single-GPU step, so 4 GPUs ≈ 4× speedup for compute-bound runs. See the [Multi GPU training](./multi_gpu_training) guide for the full setup.
-
-Reference data points on a 4×H100 80 GB cluster (`accelerate launch --num_processes=4`), 5000 steps, batch 32, AdamW, dataset [`imstevenpmwork/super_poulain_draft`](https://huggingface.co/datasets/imstevenpmwork/super_poulain_draft) (~50 episodes, ~640×480 images):
-
-| Policy      | Wall-clock | `update_s` | `dataloading_s` | GPU util | Notable flags                                                                                                                  |
-| ----------- | ---------- | ---------: | --------------: | -------- | ------------------------------------------------------------------------------------------------------------------------------ |
-| `diffusion` | 16m 17s    |      0.167 |           0.015 | ~90%     | defaults (training from scratch)                                                                                               |
-| `smolvla`   | 27m 49s    |      0.312 |           0.011 | ~80%     | `--policy.path=lerobot/smolvla_base`, `freeze_vision_encoder=false`, `train_expert_only=false`                                 |
-| `pi05`      | 3h 41m     |      2.548 |           0.014 | ~95%     | `--policy.pretrained_path=lerobot/pi05_base`, `gradient_checkpointing=true`, `dtype=bfloat16`, vision encoder + expert trained |
-
-The `dataloading_s` vs. `update_s` ratio is the diagnostic that matters: when `dataloading_s` approaches `update_s`, more GPUs stop helping — your dataloader is the bottleneck and you should look at `--num_workers`, image resolution, and disk speed before adding compute.
-
-### Schedule and checkpoints
-
-If you shorten training (e.g. 5k–10k steps on a small dataset), also shorten the LR schedule with `--policy.scheduler_decay_steps≈--steps`. Otherwise the LR stays near its peak and never decays. Same for `--save_freq`.
-
-## Where to run
-
-VRAM is the first filter. Within a tier, pick by budget and availability — the `$`–`$$$$` columns are relative; check current pricing on the provider you actually use.
-
-| Class                      | VRAM  | Tier   | Comfortable for                                             |
-| -------------------------- | ----- | ------ | ----------------------------------------------------------- |
-| RTX 3090 / 4090 (consumer) | 24 GB | `$`    | Light BC, Diffusion, SmolVLA. Tight for VLAs at batch 1.    |
-| L4 / A10G (cloud)          | 24 GB | `$–$$` | Same envelope; common on Google Cloud, RunPod, AWS `g5/g6`. |
-| A100 40 GB                 | 40 GB | `$$$`  | Any policy at reasonable batch sizes.                       |
-| A100 80 GB / H100 80 GB    | 80 GB | `$$$$` | Multi-GPU clusters; large batches for VLAs.                 |
-| **CPU only**               | —     | —      | Don't train. Use Colab or rent a GPU.                       |
-
-### Hugging Face Jobs
-
-[Hugging Face Jobs](https://huggingface.co/docs/hub/jobs) lets you run training on managed HF infrastructure, billed by the second. The repo publishes a ready-to-use image: **`huggingface/lerobot-gpu:latest`**, rebuilt **every night at 02:00 UTC from `main`** ([`docker_publish.yml`](https://github.com/huggingface/lerobot/blob/main/.github/workflows/docker_publish.yml)) — so it tracks the current state of the repo, not a tagged release.
-
-```bash
-hf jobs run --flavor a10g-large huggingface/lerobot-gpu:latest \
-  bash -c "nvidia-smi && lerobot-train \
-    --policy.type=act --dataset.repo_id=<USER>/<DATASET> \
-    --policy.repo_id=<USER>/act_<task> --batch_size=8 --steps=50000"
-```
-
-Notes:
-
-- The leading `nvidia-smi` is a quick sanity check that CUDA is visible inside the container — useful to fail fast if the flavor or driver mismatched.
-- The default Job timeout is 30 minutes; pass `--timeout 4h` (or longer) for real training.
-- `--flavor` maps onto the table above: `t4-small`/`t4-medium` (T4, ACT only), `l4x1`/`l4x4` (L4 24 GB), `a10g-small/large/largex2/largex4` (A10G 24 GB scaled out), `a100-large` (A100). For the current full catalogue + pricing see [https://huggingface.co/docs/hub/jobs](https://huggingface.co/docs/hub/jobs).

docs/source/installation.mdx

@@ -207,56 +207,6 @@ pip install 'lerobot[feetech]'        # Feetech motor support
 
 _Multiple extras can be combined (e.g., `.[core_scripts,pi,pusht]`). For a full list of available extras, refer to `pyproject.toml`._
 
-### PyTorch CUDA variant (Linux only)
-
-On Linux, the install path determines which CUDA wheel you get. macOS and Windows installs use the PyPI default (MPS / CPU / CUDA-Windows wheel respectively) and can skip this section.
-
-<!-- prettier-ignore-start -->
-
-<hfoptions id="cuda_variant">
-<hfoption id="uv-source">
-
-**Source install via `uv` (`uv sync` or `uv pip install -e .`)**
-
-`torch` and `torchvision` are pinned by the project to the **CUDA 12.8** PyTorch index (`https://download.pytorch.org/whl/cu128`, driver floor **570.86**) — covers Ampere/Ada/Hopper/Blackwell GPUs. No action needed for typical NVIDIA setups.
-
-To override for a different CUDA variant:
-
-```bash
-uv pip install --force-reinstall torch torchvision \
-    --index-url https://download.pytorch.org/whl/cu126   # older drivers; or cu130 for Blackwell on driver ≥ 580
-```
-
-</hfoption>
-<hfoption id="pip-conda">
-
-**Source install via `pip`/`conda`, or `pip install lerobot` from PyPI**
-
-PyPI default torch wheel is currently a cu130-bundled Linux wheel, driver floor **580.65**.
-
-To pick a specific CUDA variant:
-
-**Using `pip` or `conda`** — install torch first with an explicit index, then lerobot:
-
-```bash
-pip install --index-url https://download.pytorch.org/whl/cu128 torch torchvision
-pip install -e ".[all]"          # source
-# — or —
-pip install lerobot              # from PyPI
-```
-
-**Using `uv` to install from PyPI** — one-liner via `--torch-backend` (uv ≥ 0.6):
-
-```bash
-uv pip install --torch-backend cu128 lerobot
-```
-
-Supported values include `auto`, `cpu`, `cu126`, `cu128`, `cu129`, `cu130`, plus various `rocm*` and `xpu`. Swap as needed for your driver.
-
-</hfoption>
-</hfoptions>
-<!-- prettier-ignore-end -->
-
 ### Troubleshooting
 
 If you encounter build errors, you may need to install additional system dependencies: `cmake`, `build-essential`, and `ffmpeg libs`.

docs/source/language_and_recipes.mdx

@@ -0,0 +1,147 @@
+# Language columns and recipes
+
+Most LeRobot datasets ship with a single `task` string per episode — fine for
+short, single-instruction skills, but not enough for the longer-horizon,
+multi-modal robot policies the field is moving toward (high-level planning,
+memory, interjections, VQA, tool use). To support those policies without
+forking the dataset format, LeRobot extends `LeRobotDataset` with two optional
+language columns and a small recipe layer that turns those rows into
+chat-style training samples on the fly.
+
+The design splits cleanly into three layers:
+
+1. **Data in the dataset** — language annotations stored next to frames in
+   `data/chunk-*/file-*.parquet` as two optional columns (`language_persistent`
+   and `language_events`). Datasets without these columns keep their existing
+   behavior.
+2. **Recipe** — a YAML file that declares which annotation rows to bind and
+   how to lay them out as chat turns (`role`, `content`, optional images,
+   optional tool calls). Recipes are pure config; no Python required to add a
+   new one.
+3. **Training format** — at sample time, `RenderMessagesStep` resolves the
+   recipe against the per-frame annotations and emits HF-style `messages` plus
+   LeRobot-specific sidecars (`message_streams`, `target_message_indices`)
+   that policy processors consume.
+
+This page describes each layer in turn.
+
+## Layer 1 — language columns in the dataset
+
+The two optional columns live next to frame data in
+`data/chunk-*/file-*.parquet`:
+
+- `language_persistent`: a list of rows broadcast across every frame in an episode for state that remains active, such as `subtask`, `plan`, and `memory`.
+- `language_events`: a list of rows only on the exact frame where an event was emitted, such as `interjection`, `vqa`, and speech tool calls.
+
+Both columns share the same row shape (event rows omit `timestamp` because the
+frame the row sits on already provides it):
+
+```text
+role: string
+content: string | null
+style: string | null
+timestamp: float64        # persistent rows only
+camera: string | null     # observation.images.* feature key, view-dependent rows only
+tool_calls: list[Json] | null
+```
+
+The `camera` field tags rows whose `content` is grounded in a specific camera
+view. Rows of view-dependent styles (`vqa` and `trace`) MUST set `camera` to
+the matching `observation.images.*` feature key. Rows of every other style —
+including `motion`, which describes robot-frame primitives in joint / Cartesian
+terms — MUST leave `camera` as `null`. Pipeline writers and the validator
+enforce this via `validate_camera_field(style, camera)`.
+
+`meta/tasks.parquet` remains the canonical source for the task. The special `${task}` recipe binding always reads that task string and does not depend on language annotations.
+
+### Architecture
+
+The language stack itself has three internal modules backing layer 1:
+
+1. `lerobot.datasets.language` defines the schema, style registry, and `column_for_style`.
+2. `lerobot.datasets.language_render` resolves rows and renders messages.
+3. `RenderMessagesStep` turns dataset samples into `messages`, `message_streams`, and `target_message_indices`.
+
+`LeRobotDataset` stays recipe-agnostic. It passes `language_persistent` and `language_events` through when present, and unannotated datasets keep their existing behavior.
+
+### Temporal semantics
+
+Persistent styles are active after emission until replaced:
+
+- `active_at(t, style=subtask)`
+- `nth_prev(style=memory, offset=1)`
+- `nth_next(style=subtask, offset=1)`
+
+Event styles only exist on their exact timestamp:
+
+- `emitted_at(t, style=interjection)`
+- `emitted_at(t, style=vqa, role=user, camera=observation.images.top)`
+- `emitted_at(t, role=assistant, tool_name=say)`
+
+Exact event matching has no tolerance window, so writers must stamp event rows with frame timestamps from the parquet data.
+
+### View-dependent resolution
+
+For view-dependent styles (`vqa` and `trace`), the resolver gains a
+`camera=` filter parallel to `role=` and `tool_name=`. Datasets with multiple
+cameras typically emit one (`vqa`, `user`) + (`vqa`, `assistant`) pair per
+camera at the same timestamp; without `camera=`, those resolvers see two
+matches and raise an ambiguity error. Recipes consume each camera through its
+own binding plus a matching image block, e.g.
+
+```yaml
+ask_vqa_top:
+  bindings:
+    vqa_query: "emitted_at(t, style=vqa, role=user, camera=observation.images.top)"
+    vqa: "emitted_at(t, style=vqa, role=assistant, camera=observation.images.top)"
+  messages:
+    - role: user
+      stream: high_level
+      if_present: vqa_query
+      content:
+        - { type: image, feature: observation.images.top }
+        - { type: text, text: "${vqa_query}" }
+    - {
+        role: assistant,
+        content: "${vqa}",
+        stream: high_level,
+        target: true,
+        if_present: vqa,
+      }
+```
+
+Add one such sub-recipe per camera the dataset records.
+
+## Layer 2 — recipe anatomy
+
+Recipes are YAML files backed by `TrainingRecipe` and `MessageTurn`. They
+declare which annotation rows to pull (via `bindings`) and how to compose them
+into chat turns (`messages`).
+
+```yaml
+messages:
+  - { role: user, content: "${task}", stream: high_level }
+  - { role: assistant, content: "${subtask}", stream: low_level, target: true }
+```
+
+A recipe can also branch into a weighted **blend** of sub-recipes. At sample
+time, exactly one branch is selected deterministically from the sample index,
+so different frames train different objectives (e.g. memory updates vs.
+low-level execution vs. VQA) without any Python wiring.
+
+## Layer 3 — training format
+
+Rendered samples use HF-style chat messages plus LeRobot sidecars:
+
+```python
+sample["messages"]
+sample["message_streams"]
+sample["target_message_indices"]
+```
+
+The renderer does not apply a tokenizer chat template. Policy processors decide how to serialize the messages for their backbone, which keeps the same dataset usable across SmolVLA, Pi0.5, and any future VLM that expects OpenAI-style chat messages.
+
+## Graceful absence
+
+If both language columns are missing, `None`, or empty, `RenderMessagesStep` is a no-op.
+If an event-scoped branch is selected on a frame without the required event row, rendering returns `None`, allowing a loader to retry another sample.

docs/source/tools.mdx

@@ -0,0 +1,210 @@
+# Tools
+
+LeRobot v3.1 supports **tool calls** in policies — assistant messages can
+emit structured invocations like `say(text="OK, starting now")` that the
+runtime dispatches to a real implementation (TTS, controller, logger, …).
+
+This page covers:
+
+1. Where the tool catalog lives.
+2. How the annotation pipeline produces tool-call atoms.
+3. How to add your own tool.
+
+## Where tools are declared
+
+Two layers.
+
+**The catalog** — a list of OpenAI-style function schemas — lives at
+`meta/info.json["tools"]` on each dataset. Example:
+
+```json
+{
+  "features": { "...": "..." },
+  "tools": [
+    {
+      "type": "function",
+      "function": {
+        "name": "say",
+        "description": "Speak a short utterance to the user via the TTS executor.",
+        "parameters": {
+          "type": "object",
+          "properties": {
+            "text": {
+              "type": "string",
+              "description": "The verbatim text to speak."
+            }
+          },
+          "required": ["text"]
+        }
+      }
+    }
+  ]
+}
+```
+
+Read it via the dataset metadata accessor:
+
+```python
+from lerobot.datasets.dataset_metadata import LeRobotDatasetMetadata
+
+meta = LeRobotDatasetMetadata(repo_id="pepijn/super_poulain_final_annotations")
+tools = meta.tools     # list[dict] — OpenAI tool schemas
+```
+
+If the dataset's `info.json` doesn't declare any tools, `meta.tools`
+returns `DEFAULT_TOOLS` from `lerobot.datasets.language` — currently a
+single-entry list with the canonical `say` schema. So unannotated
+datasets and chat-template consumers keep working without any
+configuration:
+
+```python
+prompt_str = tokenizer.apply_chat_template(
+    sample["messages"],
+    tools=meta.tools,                 # works either way
+    add_generation_prompt=False,
+    tokenize=False,
+)
+```
+
+**The implementations** — runnable Python — will live under
+`src/lerobot/tools/`, one file per tool. The runtime dispatcher and
+the canonical `say` implementation (wrapping Kyutai's pocket-tts) are
+not part of the catalog layer described here; today this layer ships
+only the schema storage and the `DEFAULT_TOOLS` fallback constant.
+
+## Per-row tool _invocations_
+
+The catalog above describes _what can be called_. The actual _call_ — the
+function name plus the argument values — is stored per-row, on the
+assistant atoms in `language_events`:
+
+```python
+{
+  "role": "assistant",
+  "content": null,
+  "style": null,
+  "timestamp": 12.4,
+  "camera": null,
+  "tool_calls": [
+    { "type": "function",
+      "function": { "name": "say", "arguments": { "text": "On it." } } }
+  ]
+}
+```
+
+Recipes splice these into rendered messages via `tool_calls_from`:
+
+```yaml
+user_interjection_response:
+  bindings:
+    speech: "emitted_at(t, role=assistant, tool_name=say)"
+  messages:
+    - { role: user, content: "${task}", stream: high_level }
+    - {
+        role: assistant,
+        content: "${current_plan}",
+        stream: high_level,
+        target: true,
+        tool_calls_from: speech,
+      }
+```
+
+The model's training target is one assistant turn that carries both the
+plan text _and_ the `say` tool call. At inference, the runtime parses
+the generated text back into structured `tool_calls` and dispatches to
+the matching implementation.
+
+## How to add your own tool
+
+> **Note:** Steps 2 and 3 below describe the runtime layer
+> (`src/lerobot/tools/`, the `Tool` protocol, `TOOL_REGISTRY`,
+> `get_tools(meta)`) which is not part of the catalog layer shipped
+> today — those modules don't yet exist in the tree. Step 1 alone is
+> enough to make the tool visible to the chat template via
+> `meta.tools` so the model can learn to _generate_ the call;
+> executing the call at inference requires the runtime layer.
+
+Three steps. Concrete example: a `record_observation` tool the policy
+can call to capture an extra observation outside the regular control
+loop.
+
+### Step 1 — declare the schema
+
+Add an entry under `meta/info.json["tools"]`. Either edit the file
+directly on disk _before_ running the annotation pipeline (it'll be
+preserved) or hand it to `lerobot-annotate` via a config flag.
+
+```json
+{
+  "tools": [
+    { "type": "function", "function": { "name": "say", "...": "..." } },
+    {
+      "type": "function",
+      "function": {
+        "name": "record_observation",
+        "description": "Capture a high-resolution still image for the user.",
+        "parameters": {
+          "type": "object",
+          "properties": {
+            "label": {
+              "type": "string",
+              "description": "Short label for the saved image."
+            }
+          },
+          "required": ["label"]
+        }
+      }
+    }
+  ]
+}
+```
+
+The schema follows OpenAI's function-calling convention exactly, so the
+chat template can render it natively.
+
+### Step 2 — implement the call
+
+Create `src/lerobot/tools/record_observation.py`:
+
+```python
+from .base import Tool
+from typing import Any
+
+RECORD_OBSERVATION_SCHEMA: dict[str, Any] = { "...": "..." }   # mirrors the JSON above
+
+
+class RecordObservationTool:
+    name = "record_observation"
+    schema = RECORD_OBSERVATION_SCHEMA
+
+    def __init__(self, schema: dict | None = None, output_dir: str = "."):
+        self.output_dir = output_dir
+
+    def call(self, arguments: dict) -> str:
+        label = arguments["label"]
+        # ... save the latest camera frame to <output_dir>/<label>.png ...
+        return f"saved {label}.png"
+```
+
+One file per tool keeps dependencies isolated — `record_observation`
+might pull `pillow`, while `say` pulls `pocket-tts`. Users installing
+only the tools they need avoid heavy transitive deps.
+
+### Step 3 — register it
+
+Add to `src/lerobot/tools/registry.py`:
+
+```python
+from .record_observation import RecordObservationTool
+
+TOOL_REGISTRY["record_observation"] = RecordObservationTool
+```
+
+That's it. At runtime `get_tools(meta)` looks up each schema in
+`meta.tools`, instantiates the matching registered class, and returns
+a name → instance dict the dispatcher can route into.
+
+If you want to use a tool _without_ writing an implementation (e.g. for
+training-time chat-template formatting only), step 1 alone is enough —
+the model still learns to _generate_ the call. Steps 2 and 3 are only
+needed to actually _execute_ it at inference.

examples/omx/README.md

@@ -1,136 +0,0 @@
-# OMX Follower — Cube Pick And Place Example
-
-This is an example of what is possible to do with LeRobot on a physical setup.
-It is a WIP and being used internally at LeRobot and specific to our setup, but we hope it can be a useful reference for how to use LeRobot APIs and CLIs.
-
-It includes an end-to-end example for the **OMX Follower** robot arm: pick and place a cube dataset, train a policy, and deploy it autonomously.
-
-## Hardware
-
-| Component | Value                                |
-| --------- | ------------------------------------ |
-| Robot     | OMX Follower                         |
-| Cameras   | 2× OpenCV cameras (wrist + top-down) |
-
-## Scripts
-
-| Script                 | Purpose                                                         |
-| ---------------------- | --------------------------------------------------------------- |
-| `reset_environment.py` | Standalone utility: sweep workspace, grab cube, place cube      |
-| `record_grab.py`       | Automated data collection: reset → place → record grab episodes |
-
-## Setup
-
-Make sure you have LeRobot installed in your env. (See [the installation guide](https://huggingface.co/docs/lerobot/installation))
-
-Next, we will declare some environment variables for convenience. Adjust the camera indices and robot port to match your system configuration.
-
-```bash
-export ROBOT_PORT=/dev/ttyACM0
-export TELEOP_PORT=/dev/ttyACM1
-export HF_USERNAME=<your_hf_username>
-export ROBOT_CAMERAS="{ wrist: {type: opencv, index_or_path: 0, width: 640, height: 480, fps: 30, fourcc: MJPG}, top: {type: opencv, index_or_path: 2, width: 640, height: 480, fps: 30, fourcc: MJPG} }"
-```
-
-## Step 1 — Collect Data
-
-```bash
-lerobot-record \
-    --robot.type=omx_follower \
-    --robot.port=$ROBOT_PORT \
-    --robot.id=omx_follower \
-    --robot.cameras="$ROBOT_CAMERAS" \
-    --teleop.type=omx_leader \
-    --teleop.port=$TELEOP_PORT \
-    --teleop.id=omx_leader \
-    --dataset.repo_id=$HF_USERNAME/omx_pickandplace \
-    --dataset.root=data/omx_pickandplace \
-    --dataset.num_episodes=50 \
-    --dataset.single_task="Pick the cube and place it in the blue square" \
-    --dataset.streaming_encoding=true \
-    --dataset.push_to_hub=true
-```
-
-### Bonus Auto-Collect script
-
-/!\ This is specific to our setup and the task of picking and placing a cube. It is not a general-purpose data collection script. As you may notice, it doesn't require a teleop.
-
-```bash
-python -m examples.omx.record_grab \
-    --robot.type=omx_follower \
-    --robot.port=$ROBOT_PORT \
-    --robot.id=omx_follower \
-    --robot.cameras="$ROBOT_CAMERAS" \
-    --dataset.repo_id=$HF_USERNAME/omx_pickandplace \
-    --dataset.root=data/omx_pickandplace \
-    --dataset.num_episodes=50 \
-    --dataset.single_task="Pick the cube and place it in the blue square" \
-    --dataset.streaming_encoding=true \
-    --dataset.push_to_hub=true
-```
-
-Each episode:
-
-1. The arm grabs the cube from the center of the workspace and places it at a random position.
-2. The arm returns to HOME.
-3. A targeted grab is recorded: HOME → approach raised → lower onto cube → grasp → lift → carry → drop → HOME.
-
-A dataset is already available here [`maximellerbach/omx_pickandplace`](https://huggingface.co/datasets/maximellerbach/omx_pickandplace), so you can skip directly to training if you want.
-
-## Step 2 — Train
-
-To train a simple `ACT` policy on the collected dataset, you can use the `lerobot-train` CLI:
-
-```bash
-lerobot-train \
-    --dataset.repo_id=$HF_USERNAME/omx_pickandplace \
-    --policy.type=act \
-    --output_dir=outputs/train/omx_pickandplace_act \
-    --policy.device=cuda \
-    --policy.repo_id=$HF_USERNAME/omx_pickandplace_act \
-    --steps=20000 \
-    --wandb.enable=true
-```
-
-A pretrained `ACT` policy is already available here [`maximellerbach/omx_pickandplace_act`](https://huggingface.co/maximellerbach/omx_pickandplace_act).
-
-## Step 3 — Rollout
-
-Use the `lerobot-rollout` CLI with base strategy:
-
-```bash
-lerobot-rollout \
-    --strategy.type=base \
-    --robot.type=omx_follower \
-    --robot.port=$ROBOT_PORT \
-    --robot.id=omx_follower \
-    --robot.cameras="$ROBOT_CAMERAS" \
-    --policy.path=$HF_USERNAME/omx_pickandplace_act \
-```
-
-For continuous recording with automatic upload (sentry mode):
-
-```bash
-lerobot-rollout \
-    --strategy.type=sentry \
-    --strategy.upload_every_n_episodes=10 \
-    --robot.type=omx_follower \
-    --robot.port=$ROBOT_PORT \
-    --robot.id=omx_follower \
-    --robot.cameras="$ROBOT_CAMERAS" \
-    --policy.path=$HF_USERNAME/omx_pickandplace_act \
-    --dataset.repo_id=$HF_USERNAME/rollout_omx_pickandplace_act \
-```
-
-## Environment Reset Utility
-
-Those are specific to this particular physical setup. Those are scripts that execute hardcoded sequences of actions on the robot to reset the environment, which is useful for data collection and evaluation. They are not general-purpose scripts.
-
-`reset_environment.py` can be run standalone to prepare the workspace:
-
-```bash
-# Grab cube + place it at a random position on the left side
-python -m examples.omx.reset_environment --port $ROBOT_PORT --mode grab_and_place
-```
-
-It also exposes `grab_cube(robot)` and `place_cube(robot)` for use in custom scripts.

examples/omx/record_grab.py

@@ -1,422 +0,0 @@
-#!/usr/bin/env python3
-"""
-Auto-record grab episodes for the OMX robot arm.
-
-Each episode cycle:
-  1. grab_and_place  — grab cube from workspace center and place at a random (pan, reach) position
-  2. HOME            — return arm to home with gripper open
-  3. record_grab     — execute a targeted grab to the stored position while recording
-                       observations + actions to a LeRobotDataset
-
-Usage (run from repo root):
-    python -m examples.omx.record_grab \\
-        --robot.type=omx_follower \\
-        --robot.port=/dev/ttyACM0 \\
-        --robot.id=omx_follower \\
-        --robot.cameras="{ wrist: {type: opencv, index_or_path: 6, width: 640, height: 480, fps: 30, fourcc: MJPG}, top: {type: opencv, index_or_path: 4, width: 640, height: 480, fps: 30, fourcc: MJPG} }" \\
-        --dataset.repo_id=<hf_username>/<dataset_name> \\
-        --dataset.root=data/omx_grab \\
-        --dataset.num_episodes=50 \\
-        --dataset.single_task="Grab the cube" \\
-        --dataset.streaming_encoding=true
-"""
-
-import logging
-from dataclasses import dataclass
-from pprint import pformat
-
-import numpy as np
-
-from lerobot.cameras import CameraConfig  # noqa: F401
-from lerobot.cameras.opencv import OpenCVCameraConfig  # noqa: F401
-from lerobot.configs import parser
-from lerobot.configs.dataset import DatasetRecordConfig
-from lerobot.datasets import (
-    LeRobotDataset,
-    VideoEncodingManager,
-    aggregate_pipeline_dataset_features,
-    create_initial_features,
-)
-from lerobot.processor import make_default_processors
-from lerobot.robots import RobotConfig, make_robot_from_config
-from lerobot.robots.omx_follower import OmxFollower
-from lerobot.utils.constants import ACTION, OBS_STR
-from lerobot.utils.feature_utils import build_dataset_frame, combine_feature_dicts
-from lerobot.utils.robot_utils import precise_sleep
-
-from .reset_environment import (
-    APPROACH_SPEED,
-    GRIPPER_CLOSE_POS,
-    HOME_POSE,
-    PUSH_END_ELBOW_FLEX,
-    PUSH_END_SHOULDER_LIFT,
-    PUSH_START_ELBOW_FLEX,
-    PUSH_START_SHOULDER_LIFT,
-    array_to_pose,
-    grab_cube,
-    horizontal_wrist_flex,
-    move_to_pose,
-    place_cube,
-    pose_to_array,
-)
-
-# ── Grab-episode motion parameters ────────────────────────────────────────────
-
-# Shoulder-lift offset for the raised approach phase (subtracted from the target sl, arm is higher).
-GRAB_RAISE_SL_OFFSET = 20.0
-GRAB_LOWER_SPEED = 20.0
-RECORD_SPEED = 30.0
-
-# Pose the arm travels to after closing the gripper (cube held).
-GRAB_CARRY_POSE = {
-    "shoulder_pan.pos": -23.0,
-    "shoulder_lift.pos": 5.0,
-    "elbow_flex.pos": 18.0,
-    "wrist_flex.pos": -14.0,
-    "wrist_roll.pos": 0.0,
-    "gripper.pos": GRIPPER_CLOSE_POS,
-}
-
-# Per-joint jitter limits (degrees) applied to transit waypoints for human-like variation.
-# Cube-approach and carry poses are never jittered to preserve precision.
-_JITTER_LIMITS: dict[str, float] = {
-    "shoulder_pan.pos": 5.0,
-    "shoulder_lift.pos": 4.0,
-    "elbow_flex.pos": 4.0,
-    "wrist_flex.pos": 3.0,
-    "wrist_roll.pos": 2.0,
-    "gripper.pos": 0.0,
-}
-
-
-def _jitter_pose(pose: dict, rng: np.random.Generator) -> dict:
-    """Return a copy of pose with independent per-joint random perturbations."""
-    return {
-        k: v + rng.uniform(-_JITTER_LIMITS.get(k, 0.0), _JITTER_LIMITS.get(k, 0.0)) for k, v in pose.items()
-    }
-
-
-def _random_stuck_pose(rng: np.random.Generator) -> dict:
-    """Return a physically plausible stuck pose (failed grasp), gripper closed.
-
-    ef bounds are piecewise-linear in sl so the arm stays in a reachable,
-    table-safe envelope across the full sl range:
-      sl=-50 → ef ∈ [  0,  50]   (arm raised, can be bent forward)
-      sl=  0 → ef ∈ [-25,  25]   (mid reach)
-      sl= 30 → ef ∈ [-20,   0]   (arm extended, little room to flex)
-    wrist_flex is randomly offset from the horizontal value.
-    """
-    pan = float(rng.uniform(-5.0, 35.0))
-    sl = float(rng.uniform(-50.0, 30.0))
-
-    if sl <= 0.0:
-        alpha = (sl + 50.0) / 50.0  # 0 at sl=-50, 1 at sl=0
-        ef_lo = alpha * -25.0  # 0 → -25
-        ef_hi = 50.0 + alpha * -25.0  # 50 → 25
-    else:
-        alpha = sl / 30.0  # 0 at sl=0, 1 at sl=30
-        ef_lo = -25.0 + alpha * 5.0  # -25 → -20
-        ef_hi = 25.0 + alpha * -25.0  # 25 → 0
-
-    ef = float(rng.uniform(ef_lo, ef_hi))
-    wf = horizontal_wrist_flex(sl, ef) + float(rng.uniform(-15.0, 15.0))
-    return {
-        "shoulder_pan.pos": pan,
-        "shoulder_lift.pos": sl,
-        "elbow_flex.pos": ef,
-        "wrist_flex.pos": wf,
-        "wrist_roll.pos": float(rng.uniform(-15.0, 15.0)),
-        "gripper.pos": GRIPPER_CLOSE_POS,
-    }
-
-
-logger = logging.getLogger(__name__)
-
-
-@dataclass
-class OmxRecordGrabConfig:
-    robot: RobotConfig
-    dataset: DatasetRecordConfig
-    # Resume recording on an existing dataset.
-    resume: bool = False
-    # Fraction of episodes that start from a random stuck pose (gripper closed) to
-    # generate recovery data.  0.0 = disabled, 1.0 = all episodes are recovery starts.
-    recovery_prob: float = 0.5
-
-
-def record_episode_spline(
-    robot: OmxFollower,
-    waypoints: list[dict],
-    speeds: list[float],
-    dataset: LeRobotDataset,
-    task: str,
-) -> None:
-    """Execute a Catmull-Rom-style spline through waypoints, recording each frame.
-
-    Segment durations are parameterized from the maximum absolute joint delta
-    between consecutive waypoints divided by the requested segment speed,
-    producing non-uniform timing in joint space. Interior tangents are derived
-    from the adjacent per-segment velocities, with clamped (zero-velocity)
-    endpoints so the arm starts and stops smoothly. Each segment is cubic
-    Hermite, giving C1 continuity at every waypoint.
-    """
-    pts = [pose_to_array(w) for w in waypoints]
-    n = len(pts)
-
-    # Steps and duration per segment
-    n_steps_list = []
-    timestamps = []
-    for i in range(n - 1):
-        max_dist = float(np.max(np.abs(pts[i + 1] - pts[i])))
-        ns = max(1, int(max_dist / speeds[i] * dataset.fps)) if max_dist >= 0.5 else 0
-        n_steps_list.append(ns)
-        timestamps.append(ns / dataset.fps)
-
-    # Velocity tangents (deg/sec) — clamped at endpoints, Catmull-Rom for interior
-    vels = [np.zeros_like(pts[0])]
-    for i in range(1, n - 1):
-        v_prev = (pts[i] - pts[i - 1]) / timestamps[i - 1] if timestamps[i - 1] > 0 else np.zeros_like(pts[0])
-        v_next = (pts[i + 1] - pts[i]) / timestamps[i] if timestamps[i] > 0 else np.zeros_like(pts[0])
-        vels.append(0.5 * (v_prev + v_next))
-    vels.append(np.zeros_like(pts[0]))
-
-    dt = 1.0 / dataset.fps
-    for seg in range(n - 1):
-        ns = n_steps_list[seg]
-        if ns == 0:
-            continue
-        p0, p1 = pts[seg], pts[seg + 1]
-        # Scale velocity (deg/sec) to t-space tangent (deg/t-unit, where t: 0→1 over ns steps)
-        m0 = vels[seg] * timestamps[seg]
-        m1 = vels[seg + 1] * timestamps[seg]
-
-        for step in range(1, ns + 1):
-            t = step / ns
-            h00 = 2 * t**3 - 3 * t**2 + 1
-            h10 = t**3 - 2 * t**2 + t
-            h01 = -2 * t**3 + 3 * t**2
-            h11 = t**3 - t**2
-            commanded = h00 * p0 + h10 * m0 + h01 * p1 + h11 * m1
-
-            action = array_to_pose(commanded)
-            robot.send_action(action)
-            obs = robot.get_observation()
-            obs_frame = build_dataset_frame(dataset.features, obs, prefix=OBS_STR)
-            action_frame = build_dataset_frame(dataset.features, action, prefix=ACTION)
-            dataset.add_frame({**obs_frame, **action_frame, "task": task})
-            precise_sleep(dt)
-
-
-def record_grab_episode(
-    robot: OmxFollower,
-    dataset: LeRobotDataset,
-    pan: float,
-    t: float,
-    task: str,
-    recovery_start: bool = False,
-) -> None:
-    """Execute a targeted grab to the stored (pan, t) position, recording every frame.
-
-    Normal sequence (initial HOME move is NOT recorded):
-      HOME → raised approach above cube → lower → close gripper
-           → raise [jittered] → retract [jittered] → GRAB_CARRY_POSE → drop → HOME
-
-    Recovery sequence (recovery_start=True): arm is moved to a random stuck pose
-    (gripper closed) without recording, then recording begins from there:
-      stuck_pose → raised approach above cube → [normal grab sequence from there]
-
-    All segments are joined by a Catmull-Rom spline (C1-continuous velocities).
-    """
-    sl = PUSH_START_SHOULDER_LIFT + t * (PUSH_END_SHOULDER_LIFT - PUSH_START_SHOULDER_LIFT)
-    ef = PUSH_START_ELBOW_FLEX + t * (PUSH_END_ELBOW_FLEX - PUSH_START_ELBOW_FLEX)
-    sl_raised = sl - GRAB_RAISE_SL_OFFSET
-    wf_horizontal = horizontal_wrist_flex(sl, ef)
-
-    rng = np.random.default_rng()
-
-    if recovery_start:
-        stuck_pose = _random_stuck_pose(rng)
-        logger.info(f"Recovery start: {stuck_pose}")
-        move_to_pose(robot, stuck_pose, APPROACH_SPEED)
-        first_waypoints = [stuck_pose]
-        first_speeds = []
-    else:
-        jittery_start = _jitter_pose(HOME_POSE, rng)
-        move_to_pose(robot, jittery_start, APPROACH_SPEED)
-        first_waypoints = [jittery_start]
-        first_speeds = []
-
-    waypoints = first_waypoints + [
-        {  # raised approach: arm above cube
-            "shoulder_pan.pos": pan,
-            "shoulder_lift.pos": sl_raised,
-            "elbow_flex.pos": ef,
-            "wrist_flex.pos": horizontal_wrist_flex(sl_raised, ef),
-            "wrist_roll.pos": 0.0,
-            "gripper.pos": 60.0,
-        },
-        {  # lower onto cube — no jitter: precision needed
-            "shoulder_pan.pos": pan,
-            "shoulder_lift.pos": sl,
-            "elbow_flex.pos": ef,
-            "wrist_flex.pos": wf_horizontal,
-            "wrist_roll.pos": 0.0,
-            "gripper.pos": 60.0,
-        },
-        {  # close gripper — no jitter: precision needed
-            "shoulder_pan.pos": pan,
-            "shoulder_lift.pos": sl,
-            "elbow_flex.pos": ef,
-            "wrist_flex.pos": wf_horizontal,
-            "wrist_roll.pos": 0.0,
-            "gripper.pos": GRIPPER_CLOSE_POS,
-        },
-        _jitter_pose(
-            {  # raise with cube
-                "shoulder_pan.pos": pan,
-                "shoulder_lift.pos": sl_raised,
-                "elbow_flex.pos": ef,
-                "wrist_flex.pos": horizontal_wrist_flex(sl_raised, ef),
-                "wrist_roll.pos": 0.0,
-                "gripper.pos": GRIPPER_CLOSE_POS,
-            },
-            rng,
-        ),
-        _jitter_pose(
-            {  # retract: fold arm toward HOME before sweeping to carry zone
-                "shoulder_pan.pos": pan * 0.25,
-                "shoulder_lift.pos": HOME_POSE["shoulder_lift.pos"] + 5.0,
-                "elbow_flex.pos": HOME_POSE["elbow_flex.pos"] - 5.0,
-                "wrist_flex.pos": 0.0,
-                "wrist_roll.pos": 0.0,
-                "gripper.pos": GRIPPER_CLOSE_POS,
-            },
-            rng,
-        ),
-        GRAB_CARRY_POSE,  # no jitter: target drop zone
-        {**GRAB_CARRY_POSE, "gripper.pos": 60.0},  # drop cube
-        HOME_POSE,
-    ]
-    speeds = first_speeds + [
-        RECORD_SPEED,  # (HOME →) raised approach
-        GRAB_LOWER_SPEED,  # raised approach → lower
-        GRAB_LOWER_SPEED,  # lower → close gripper
-        RECORD_SPEED,  # close gripper → raise
-        RECORD_SPEED,  # raise → retract
-        RECORD_SPEED,  # retract → carry pose
-        RECORD_SPEED,  # carry pose → drop
-        RECORD_SPEED,  # drop → HOME
-    ]
-
-    record_episode_spline(robot, waypoints, speeds, dataset, task)
-
-    # Dwell at HOME for ~0.5 s before next episode
-    home_action = build_dataset_frame(dataset.features, HOME_POSE, prefix=ACTION)
-    dt = 1.0 / dataset.fps
-    for _ in range(int(dataset.fps * 0.5)):
-        robot.send_action(HOME_POSE)
-        obs = robot.get_observation()
-        obs_frame = build_dataset_frame(dataset.features, obs, prefix=OBS_STR)
-        dataset.add_frame({**obs_frame, **home_action, "task": task})
-        precise_sleep(dt)
-
-
-@parser.wrap()
-def record_grab(cfg: OmxRecordGrabConfig) -> LeRobotDataset:
-    logging.basicConfig(level=logging.INFO, format="%(levelname)s: %(message)s")
-    logger.info(pformat(cfg))
-
-    robot = make_robot_from_config(cfg.robot)
-    use_videos = cfg.dataset.video
-
-    teleop_action_processor, _, robot_obs_processor = make_default_processors()
-
-    dataset_features = combine_feature_dicts(
-        aggregate_pipeline_dataset_features(
-            pipeline=teleop_action_processor,
-            initial_features=create_initial_features(action=robot.action_features),
-            use_videos=use_videos,
-        ),
-        aggregate_pipeline_dataset_features(
-            pipeline=robot_obs_processor,
-            initial_features=create_initial_features(observation=robot.observation_features),
-            use_videos=use_videos,
-        ),
-    )
-
-    num_cameras = len(robot.cameras) if hasattr(robot, "cameras") else 0
-    dataset = None
-
-    try:
-        if cfg.resume:
-            dataset = LeRobotDataset.resume(
-                cfg.dataset.repo_id,
-                root=cfg.dataset.root,
-                streaming_encoding=cfg.dataset.streaming_encoding,
-                batch_encoding_size=cfg.dataset.video_encoding_batch_size,
-                vcodec=cfg.dataset.vcodec,
-                encoder_threads=cfg.dataset.encoder_threads,
-                image_writer_processes=cfg.dataset.num_image_writer_processes if num_cameras > 0 else 0,
-                image_writer_threads=cfg.dataset.num_image_writer_threads_per_camera * num_cameras
-                if num_cameras > 0
-                else 0,
-            )
-        else:
-            cfg.dataset.stamp_repo_id()
-            dataset = LeRobotDataset.create(
-                cfg.dataset.repo_id,
-                cfg.dataset.fps,
-                root=cfg.dataset.root,
-                robot_type=robot.name,
-                features=dataset_features,
-                use_videos=use_videos,
-                streaming_encoding=cfg.dataset.streaming_encoding,
-                batch_encoding_size=cfg.dataset.video_encoding_batch_size,
-                vcodec=cfg.dataset.vcodec,
-                encoder_threads=cfg.dataset.encoder_threads,
-                image_writer_processes=cfg.dataset.num_image_writer_processes if num_cameras > 0 else 0,
-                image_writer_threads=cfg.dataset.num_image_writer_threads_per_camera * num_cameras
-                if num_cameras > 0
-                else 0,
-            )
-
-        robot.connect(calibrate=True)
-
-        rng = np.random.default_rng()
-        with VideoEncodingManager(dataset):
-            for episode_idx in range(cfg.dataset.num_episodes):
-                logger.info(f"=== Episode {episode_idx + 1}/{cfg.dataset.num_episodes} ===")
-
-                logger.info("Step 1: grabbing and placing cube...")
-                grab_cube(robot)
-                pan, t = place_cube(robot)
-                logger.info(f"Cube placed at pan={pan:.1f}, reach={t:.2f}")
-
-                recovery_start = cfg.recovery_prob > 0 and float(rng.random()) < cfg.recovery_prob
-                logger.info(f"Step 2: recording {'recovery ' if recovery_start else ''}grab episode...")
-                record_grab_episode(
-                    robot,
-                    dataset,
-                    pan,
-                    t,
-                    cfg.dataset.single_task,
-                    recovery_start=recovery_start,
-                )
-
-                dataset.save_episode()
-                logger.info(f"Episode {episode_idx + 1} saved.")
-
-    finally:
-        if dataset:
-            dataset.finalize()
-        if robot.is_connected:
-            robot.disconnect()
-
-    if cfg.dataset.push_to_hub and dataset and dataset.num_episodes > 0:
-        dataset.push_to_hub(tags=cfg.dataset.tags, private=cfg.dataset.private)
-
-    return dataset
-
-
-if __name__ == "__main__":
-    record_grab()

examples/omx/reset_environment.py

@@ -1,267 +0,0 @@
-#!/usr/bin/env python3
-"""
-Auto-reset and cube-grab utility for the OMX robot arm.
-
-Provides:
-  - grab_cube(robot): sweep workspace, center cube, close gripper
-  - place_cube(robot): carry cube to a random position, release
-
-Standalone usage (run from repo root):
-    python -m examples.omx.reset_environment --port /dev/ttyACM1 --mode grab
-    python -m examples.omx.reset_environment --port /dev/ttyACM1 --mode grab_and_place
-
-Joint range: -100 to 100 for arm joints; gripper: 50 = closed, 80 = open.
-
-To read current joint values for calibration, add after robot.connect():
-    obs = robot.get_observation()
-    print({k: round(obs[k], 1) for k in JOINT_NAMES})
-    robot.disconnect(); raise SystemExit
-
-Parallel-to-ground IK: wrist_flex = WRIST_HORIZONTAL_OFFSET - shoulder_lift - elbow_flex.
-Linear interpolation preserves this constraint between any two poses that satisfy it.
-"""
-
-import argparse
-import logging
-
-import numpy as np
-
-from lerobot.robots.omx_follower import OmxFollower, OmxFollowerConfig
-from lerobot.robots.robot import Robot
-from lerobot.utils.robot_utils import precise_sleep
-
-logger = logging.getLogger(__name__)
-
-# ── Poses ─────────────────────────────────────────────────────────────────────
-
-HOME_POSE = {
-    "shoulder_pan.pos": 0.0,
-    "shoulder_lift.pos": -50.0,
-    "elbow_flex.pos": 50.0,
-    "wrist_flex.pos": 0.0,
-    "wrist_roll.pos": 0.0,
-    "gripper.pos": 60.0,
-}
-
-SWEEP_WAYPOINTS = [
-    {
-        "shoulder_pan.pos": -60.0,
-        "shoulder_lift.pos": 50.0,
-        "elbow_flex.pos": -60.0,
-        "wrist_flex.pos": -20.0,
-        "wrist_roll.pos": 0.0,
-        "gripper.pos": 60.0,
-    },
-    {
-        "shoulder_pan.pos": -30.0,
-        "shoulder_lift.pos": 50.0,
-        "elbow_flex.pos": -60.0,
-        "wrist_flex.pos": -5.0,
-        "wrist_roll.pos": 0.0,
-        "gripper.pos": 60.0,
-    },
-    {
-        "shoulder_pan.pos": 20.0,
-        "shoulder_lift.pos": 50.0,
-        "elbow_flex.pos": -55.0,
-        "wrist_flex.pos": -5.0,
-        "wrist_roll.pos": 0.0,
-        "gripper.pos": 60.0,
-    },
-]
-
-# ── Motion parameters ─────────────────────────────────────────────────────────
-
-CONTROL_HZ = 30
-APPROACH_SPEED = 50.0
-SWEEP_SPEED = 40.0
-
-# ── Grab-sequence parameters ──────────────────────────────────────────────────
-
-GRAB_PAN = 0.0
-SWEEP_LEFT_PAN = -60.0
-SWEEP_RIGHT_PAN = 60.0
-SWEEP_END_OFFSET = 5.0  # stop before center so the cube isn't pushed past GRAB_PAN
-SWEEP_END_PAN_RANGE = (15.0, 20.0)
-
-SWEEP_LOW_SHOULDER_LIFT = 50.0
-SWEEP_LOW_ELBOW_FLEX_START = -60.0
-SWEEP_LOW_ELBOW_FLEX_END = -55.0
-
-SWEEP_HIGH_WRIST_FLEX = -20.0  # wrist tilted up during high approach to clear obstacles
-
-PUSH_START_SHOULDER_LIFT = 0.0
-PUSH_START_ELBOW_FLEX = 45.0
-PUSH_END_SHOULDER_LIFT = 50.0
-PUSH_END_ELBOW_FLEX = -50.0
-# Subtracted from shoulder_lift during the push sweep to clear the platform surface.
-# Does not affect the grab-target interpolation in record_grab.py.
-PUSH_RAISE_OFFSET = 5.0
-
-WRIST_HORIZONTAL_OFFSET = 0.0  # tune if gripper tilts during push: + tilts nose up, - down
-GRIPPER_CLOSE_POS = 50.0
-
-PLACE_LEFT_PAN_RANGE = (5.0, 30.0)  # random pan range for cube placement on the left side
-PLACE_REACH_RANGE = (0.1, 0.7)  # 0 = arm retracted (PUSH_START), 1 = fully extended (PUSH_END)
-
-JOINT_NAMES = [
-    "shoulder_pan.pos",
-    "shoulder_lift.pos",
-    "elbow_flex.pos",
-    "wrist_flex.pos",
-    "wrist_roll.pos",
-    "gripper.pos",
-]
-
-# ── Helpers ───────────────────────────────────────────────────────────────────
-
-
-def pose_to_array(pose: dict) -> np.ndarray:
-    return np.array([pose[k] for k in JOINT_NAMES])
-
-
-def array_to_pose(arr: np.ndarray) -> dict:
-    return {k: float(arr[i]) for i, k in enumerate(JOINT_NAMES)}
-
-
-def horizontal_wrist_flex(shoulder_lift: float, elbow_flex: float) -> float:
-    return WRIST_HORIZONTAL_OFFSET - shoulder_lift - elbow_flex
-
-
-def _low_sweep_pose(pan: float, elbow_flex: float, wrist_flex: float | None = None) -> dict:
-    sl = SWEEP_LOW_SHOULDER_LIFT
-    return {
-        "shoulder_pan.pos": pan,
-        "shoulder_lift.pos": sl,
-        "elbow_flex.pos": elbow_flex,
-        "wrist_flex.pos": horizontal_wrist_flex(sl, elbow_flex) if wrist_flex is None else wrist_flex,
-        "wrist_roll.pos": 0.0,
-        "gripper.pos": 60.0,
-    }
-
-
-def _high_sweep_pose(pan: float) -> dict:
-    return {**HOME_POSE, "shoulder_pan.pos": pan, "wrist_flex.pos": SWEEP_HIGH_WRIST_FLEX}
-
-
-def _push_pose(shoulder_lift: float, elbow_flex: float, pan: float = GRAB_PAN, gripper: float = 70.0) -> dict:
-    return {
-        "shoulder_pan.pos": pan,
-        "shoulder_lift.pos": shoulder_lift,
-        "elbow_flex.pos": elbow_flex,
-        "wrist_flex.pos": horizontal_wrist_flex(shoulder_lift, elbow_flex),
-        "wrist_roll.pos": 0.0,
-        "gripper.pos": gripper,
-    }
-
-
-def move_to_pose(robot: Robot, target: dict, speed: float) -> None:
-    """Interpolate from current position to target at the given speed (units/s)."""
-    obs = robot.get_observation()
-    current = np.array([obs[k] for k in JOINT_NAMES])
-    goal = pose_to_array(target)
-
-    max_distance = float(np.max(np.abs(goal - current)))
-    if max_distance < 0.5:
-        return
-
-    n_steps = max(1, int(max_distance / speed * CONTROL_HZ))
-    dt = 1.0 / CONTROL_HZ
-    for step in range(1, n_steps + 1):
-        t = step / n_steps
-        robot.send_action(array_to_pose(current + t * (goal - current)))
-        precise_sleep(dt)
-
-
-# ── Sequences ─────────────────────────────────────────────────────────────────
-
-
-def grab_cube(robot: Robot) -> None:
-    """Left sweep → right sweep → extend arm parallel to ground → close gripper."""
-    move_to_pose(robot, HOME_POSE, APPROACH_SPEED)
-
-    for pan, end_pan in [
-        (SWEEP_LEFT_PAN, GRAB_PAN - SWEEP_END_OFFSET),
-        (SWEEP_RIGHT_PAN, GRAB_PAN + SWEEP_END_OFFSET),
-    ]:
-        logger.info(f"Sweeping {'left' if pan < 0 else 'right'} → center...")
-        move_to_pose(robot, _high_sweep_pose(pan), APPROACH_SPEED)
-        move_to_pose(
-            robot, _low_sweep_pose(pan, SWEEP_LOW_ELBOW_FLEX_START, wrist_flex=-20.0), APPROACH_SPEED
-        )
-        move_to_pose(robot, _low_sweep_pose(end_pan, SWEEP_LOW_ELBOW_FLEX_END, wrist_flex=0.0), SWEEP_SPEED)
-        move_to_pose(robot, HOME_POSE, APPROACH_SPEED)
-
-    logger.info("Extending to push cube into gripper...")
-    move_to_pose(
-        robot,
-        _push_pose(PUSH_START_SHOULDER_LIFT - PUSH_RAISE_OFFSET, PUSH_START_ELBOW_FLEX),
-        APPROACH_SPEED,
-    )
-    move_to_pose(
-        robot,
-        _push_pose(PUSH_END_SHOULDER_LIFT - PUSH_RAISE_OFFSET, PUSH_END_ELBOW_FLEX),
-        SWEEP_SPEED,
-    )
-
-    logger.info("Closing gripper...")
-    move_to_pose(
-        robot,
-        _push_pose(PUSH_END_SHOULDER_LIFT, PUSH_END_ELBOW_FLEX, gripper=GRIPPER_CLOSE_POS),
-        APPROACH_SPEED,
-    )
-
-    logger.info("Grab complete.")
-
-
-def place_cube(robot: Robot) -> tuple[float, float]:
-    """Carry the cube (gripper closed) to a random position on the left side, then release.
-
-    Returns:
-        (pan, t): pan angle and reach scalar [0, 1] of the placement position.
-    """
-    pan = float(np.random.uniform(*PLACE_LEFT_PAN_RANGE))
-    t = float(np.random.uniform(*PLACE_REACH_RANGE))
-    sl = PUSH_START_SHOULDER_LIFT + t * (PUSH_END_SHOULDER_LIFT - PUSH_START_SHOULDER_LIFT)
-    ef = PUSH_START_ELBOW_FLEX + t * (PUSH_END_ELBOW_FLEX - PUSH_START_ELBOW_FLEX)
-    logger.info(f"Placing cube at pan={pan:.1f}, reach={t:.2f}...")
-
-    move_to_pose(robot, {**HOME_POSE, "gripper.pos": GRIPPER_CLOSE_POS}, APPROACH_SPEED)
-    move_to_pose(
-        robot, {**HOME_POSE, "shoulder_pan.pos": pan, "gripper.pos": GRIPPER_CLOSE_POS}, APPROACH_SPEED
-    )
-    move_to_pose(robot, _push_pose(sl, ef, pan=pan, gripper=GRIPPER_CLOSE_POS), APPROACH_SPEED)
-    move_to_pose(robot, _push_pose(sl, ef, pan=pan, gripper=80.0), APPROACH_SPEED)
-    move_to_pose(robot, HOME_POSE, APPROACH_SPEED)
-    logger.info("Place complete.")
-    return pan, t
-
-
-# ── Entry point ───────────────────────────────────────────────────────────────
-
-
-def main():
-    parser = argparse.ArgumentParser(description="OMX arm reset / grab script")
-    parser.add_argument("--port", default="/dev/ttyACM1")
-    parser.add_argument("--robot_id", default="omx_follower")
-    parser.add_argument("--mode", choices=["grab", "grab_and_place"], default="grab_and_place")
-    args = parser.parse_args()
-
-    logging.basicConfig(level=logging.INFO, format="%(levelname)s: %(message)s")
-
-    robot = OmxFollower(OmxFollowerConfig(port=args.port, id=args.robot_id))
-    robot.connect(calibrate=True)
-
-    try:
-        if args.mode == "grab":
-            grab_cube(robot)
-        elif args.mode == "grab_and_place":
-            grab_cube(robot)
-            place_cube(robot)
-
-    finally:
-        robot.disconnect()
-
-
-if __name__ == "__main__":
-    main()

pyproject.toml

@@ -59,8 +59,8 @@ keywords = ["lerobot", "huggingface", "robotics",  "machine learning", "artifici
 
 dependencies = [
     # Core ML
-    "torch>=2.7,<2.12.0",
-    "torchvision>=0.22.0,<0.27.0",
+    "torch>=2.7,<2.11.0",
+    "torchvision>=0.22.0,<0.26.0",
     "numpy>=2.0.0,<2.3.0", # NOTE: Explicitly listing numpy helps the resolver converge faster. Upper bound imposed by opencv-python-headless.
     "opencv-python-headless>=4.9.0,<4.14.0",
     "Pillow>=10.0.0,<13.0.0",
@@ -95,11 +95,11 @@ dependencies = [
 
 # ── Feature-scoped extras ──────────────────────────────────
 dataset = [
-    "datasets>=4.0.0,<5.0.0",
+    "datasets>=4.7.0,<5.0.0",
     "pandas>=2.0.0,<3.0.0", # NOTE: Transitive dependency of datasets
     "pyarrow>=21.0.0,<30.0.0", # NOTE: Transitive dependency of datasets
     "lerobot[av-dep]",
-    "torchcodec>=0.3.0,<0.12.0; sys_platform != 'win32' and (sys_platform != 'linux' or (platform_machine != 'aarch64' and platform_machine != 'arm64' and platform_machine != 'armv7l')) and (sys_platform != 'darwin' or platform_machine != 'x86_64')", # NOTE: Windows support starts at version 0.7 (needs torch==2.8), ffmpeg>=8 support starts at version 0.8.1 (needs torch==2.9), system-wide ffmpeg support starts at version 0.10 (needs torch==2.10), 0.11 needs torch==2.11, 0.12 needs torch==2.12.
+    "torchcodec>=0.3.0,<0.11.0; sys_platform != 'win32' and (sys_platform != 'linux' or (platform_machine != 'aarch64' and platform_machine != 'arm64' and platform_machine != 'armv7l')) and (sys_platform != 'darwin' or platform_machine != 'x86_64')", # NOTE: Windows support starts at version 0.7 (needs torch==2.8), ffmpeg>=8 support starts at version 0.8.1 (needs torch==2.9), system-wide ffmpeg support starts at version 0.10 (needs torch==2.10).
     "jsonlines>=4.0.0,<5.0.0",
 ]
 training = [
@@ -293,20 +293,6 @@ lerobot-setup-can="lerobot.scripts.lerobot_setup_can:main"
 lerobot-rollout="lerobot.scripts.lerobot_rollout:main"
 
 # ---------------- Tool Configurations ----------------
-
-# cu128 wheels keep broad hardware reach; the driver floor is 570.86.
-# To use a different CUDA variant, reinstall torch with an explicit index, e.g.:
-#   uv pip install --force-reinstall torch torchvision \
-#       --index-url https://download.pytorch.org/whl/cu130
-[[tool.uv.index]]
-name = "pytorch-cu128"
-url = "https://download.pytorch.org/whl/cu128"
-explicit = true
-
-[tool.uv.sources]
-torch = [{ index = "pytorch-cu128", marker = "sys_platform == 'linux'" }]
-torchvision = [{ index = "pytorch-cu128", marker = "sys_platform == 'linux'" }]
-
 [tool.setuptools.package-data]
 lerobot = ["envs/*.json"]
 

src/lerobot/configs/__init__.py

@@ -24,6 +24,7 @@ Import them directly: ``from lerobot.configs.train import TrainPipelineConfig``
 from .dataset import DatasetRecordConfig
 from .default import DatasetConfig, EvalConfig, PeftConfig, WandBConfig
 from .policies import PreTrainedConfig
+from .recipe import MessageTurn, TrainingRecipe, load_recipe
 from .types import (
     FeatureType,
     NormalizationMode,
@@ -43,7 +44,10 @@ __all__ = [
     "DatasetRecordConfig",
     "DatasetConfig",
     "EvalConfig",
+    "MessageTurn",
     "PeftConfig",
     "PreTrainedConfig",
+    "TrainingRecipe",
     "WandBConfig",
+    "load_recipe",
 ]

src/lerobot/configs/recipe.py

@@ -0,0 +1,206 @@
+#!/usr/bin/env python
+
+# Copyright 2026 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.
+
+from __future__ import annotations
+
+import re
+from dataclasses import dataclass
+from pathlib import Path
+from typing import Any, Literal, get_args
+
+MessageRole = Literal["user", "assistant", "system", "tool"]
+MessageStream = Literal["high_level", "low_level"]
+
+DEFAULT_BINDINGS = {
+    "subtask": "active_at(t, style=subtask)",
+    "memory": "active_at(t, style=memory)",
+    "plan": "active_at(t, style=plan)",
+    "speech": "emitted_at(t, role=assistant, tool_name=say)",
+    "interjection": "emitted_at(t, style=interjection)",
+    "vqa": "emitted_at(t, style=vqa, role=assistant)",
+    "vqa_query": "emitted_at(t, style=vqa, role=user)",
+}
+
+PLACEHOLDER_RE = re.compile(r"\$\{([A-Za-z_][A-Za-z0-9_]*)\}")
+"""``${name}`` placeholder pattern used by both recipe binding-reference
+discovery (here) and rendered-message substitution (in ``language_render``)."""
+
+_VALID_ROLES = frozenset(get_args(MessageRole))
+_VALID_STREAMS = frozenset(get_args(MessageStream))
+
+
+@dataclass
+class MessageTurn:
+    """A single chat-style turn in a recipe template.
+
+    ``content`` may be a plain string, a list of HF-style multimodal blocks, or
+    ``None`` when ``tool_calls_from`` supplies tool-call payloads instead.
+    ``stream`` tags the turn for downstream filtering, ``target`` flags it as a
+    training target, and ``if_present`` skips the turn when the named binding
+    resolves to ``None``.
+    """
+
+    role: MessageRole
+    content: str | list[dict[str, Any]] | None = None
+    stream: MessageStream | None = None
+    target: bool = False
+    if_present: str | None = None
+    tool_calls_from: str | None = None
+
+    def __post_init__(self) -> None:
+        """Validate role, stream, and content after dataclass construction."""
+        if self.role not in _VALID_ROLES:
+            raise ValueError(f"Unsupported message role: {self.role!r}")
+        # ``stream`` is typed Optional only so the dataclass can keep its
+        # field ordering, but recipes must always tag every turn with a
+        # stream — the renderer's ``_validate_rendered`` would reject
+        # ``None`` later on. Fail at construction so the bad recipe is
+        # caught at YAML load time rather than at the first sample.
+        if self.stream is None:
+            raise ValueError(
+                f"MessageTurn(role={self.role!r}) is missing a stream — "
+                f"every turn must declare one of {sorted(_VALID_STREAMS)}."
+            )
+        if self.stream not in _VALID_STREAMS:
+            raise ValueError(f"Unsupported message stream: {self.stream!r}")
+        if self.content is None and self.tool_calls_from is None:
+            raise ValueError("MessageTurn.content is required unless tool_calls_from is set.")
+        if self.content is not None and not isinstance(self.content, (str, list)):
+            raise TypeError("MessageTurn.content must be a string, a list of HF-style blocks, or None.")
+        if isinstance(self.content, list):
+            for block in self.content:
+                if not isinstance(block, dict) or "type" not in block:
+                    raise ValueError(
+                        "Multimodal content blocks must be HF-style dictionaries with a type key."
+                    )
+
+    @classmethod
+    def from_dict(cls, data: dict[str, Any]) -> MessageTurn:
+        """Construct a :class:`MessageTurn` from a plain dictionary."""
+        return cls(**data)
+
+
+@dataclass
+class TrainingRecipe:
+    """A recipe describing how to render training samples from language rows.
+
+    A recipe is either a *message recipe* (``messages`` plus optional
+    ``bindings``) or a *blend recipe* (``blend`` mapping names to weighted
+    sub-recipes). ``weight`` is only meaningful inside a blend.
+    """
+
+    messages: list[MessageTurn] | None = None
+    bindings: dict[str, str] | None = None
+    blend: dict[str, TrainingRecipe] | None = None
+    weight: float | None = None
+
+    def __post_init__(self) -> None:
+        """Validate that exactly one of ``messages`` or ``blend`` is set."""
+        if self.messages is not None and self.blend is not None:
+            raise ValueError("TrainingRecipe must set only one of messages or blend.")
+        if self.messages is None and self.blend is None:
+            raise ValueError("TrainingRecipe must set one of messages or blend.")
+
+        if self.messages is not None:
+            self._validate_message_recipe()
+        if self.blend is not None:
+            self._validate_blend_recipe()
+
+    @classmethod
+    def from_dict(cls, data: dict[str, Any]) -> TrainingRecipe:
+        """Construct a :class:`TrainingRecipe` from a nested dictionary."""
+        data = dict(data)
+        if data.get("messages") is not None:
+            data["messages"] = [
+                turn if isinstance(turn, MessageTurn) else MessageTurn.from_dict(turn)
+                for turn in data["messages"]
+            ]
+        if data.get("blend") is not None:
+            data["blend"] = {
+                name: recipe if isinstance(recipe, TrainingRecipe) else cls.from_dict(recipe)
+                for name, recipe in data["blend"].items()
+            }
+        return cls(**data)
+
+    @classmethod
+    def from_yaml(cls, path: str | Path) -> TrainingRecipe:
+        """Load a :class:`TrainingRecipe` from a YAML file at ``path``."""
+        import yaml  # type: ignore[import-untyped]
+
+        with open(path) as f:
+            data = yaml.safe_load(f)
+        if not isinstance(data, dict):
+            raise ValueError(f"Recipe YAML must contain a mapping at the top level: {path}")
+        return cls.from_dict(data)
+
+    def _validate_message_recipe(self) -> None:
+        """Ensure every templated binding is known and at least one turn is a target."""
+        assert self.messages is not None
+        known_bindings = set(DEFAULT_BINDINGS) | set(self.bindings or {}) | {"task"}
+
+        for turn in self.messages:
+            missing = self._referenced_bindings(turn) - known_bindings
+            if missing:
+                raise ValueError(f"MessageTurn references unknown binding(s): {sorted(missing)}")
+
+        if not any(turn.target for turn in self.messages):
+            raise ValueError("Message recipes must contain at least one target turn.")
+
+    def _validate_blend_recipe(self) -> None:
+        """Ensure each blend component is a non-empty, weighted message recipe."""
+        assert self.blend is not None
+        if not self.blend:
+            raise ValueError("Blend recipes must contain at least one component.")
+
+        for name, recipe in self.blend.items():
+            if recipe.blend is not None:
+                raise ValueError(f"Blend component {name!r} cannot itself define a blend.")
+            if recipe.messages is None:
+                raise ValueError(f"Blend component {name!r} must define messages.")
+            if recipe.weight is None:
+                raise ValueError(f"Blend component {name!r} must define weight.")
+            if recipe.weight <= 0:
+                raise ValueError(f"Blend component {name!r} must have a positive weight.")
+
+    def _referenced_bindings(self, turn: MessageTurn) -> set[str]:
+        """Return the binding names that ``turn`` references via placeholders or attributes."""
+        names: set[str] = set()
+        if turn.if_present is not None:
+            names.add(turn.if_present)
+        if turn.tool_calls_from is not None:
+            names.add(turn.tool_calls_from)
+        names.update(_placeholders_in_content(turn.content))
+        return names
+
+
+def _placeholders_in_content(content: str | list[dict[str, Any]] | None) -> set[str]:
+    """Return the set of ``${name}`` placeholders found anywhere in ``content``."""
+    if content is None:
+        return set()
+    if isinstance(content, str):
+        return set(PLACEHOLDER_RE.findall(content))
+
+    names: set[str] = set()
+    for block in content:
+        for value in block.values():
+            if isinstance(value, str):
+                names.update(PLACEHOLDER_RE.findall(value))
+    return names
+
+
+def load_recipe(path: str | Path) -> TrainingRecipe:
+    """Load a :class:`TrainingRecipe` from a YAML file at ``path``."""
+    return TrainingRecipe.from_yaml(path)

src/lerobot/configs/train.py

@@ -256,9 +256,7 @@ class TrainPipelineConfig(HubMixin):
                 ) from e
 
         cli_args = kwargs.pop("cli_args", [])
-        # Legacy RA-BC migration only applies to framework-saved checkpoints (always JSON).
-        # Hand-written YAML/TOML configs are expected to use the current sample_weighting schema.
-        if config_file is not None and config_file.endswith(".json"):
+        if config_file is not None:
             with open(config_file) as f:
                 config = json.load(f)
             migrated_config = _migrate_legacy_rabc_fields(config)

src/lerobot/datasets/__init__.py

@@ -37,6 +37,14 @@ from .dataset_tools import (
 from .factory import make_dataset, resolve_delta_timestamps
 from .image_writer import safe_stop_image_writer
 from .io_utils import load_episodes, write_stats
+from .language import (
+    EVENT_ONLY_STYLES,
+    LANGUAGE_EVENTS,
+    LANGUAGE_PERSISTENT,
+    PERSISTENT_STYLES,
+    STYLE_REGISTRY,
+    column_for_style,
+)
 from .lerobot_dataset import LeRobotDataset
 from .multi_dataset import MultiLeRobotDataset
 from .pipeline_features import aggregate_pipeline_dataset_features, create_initial_features
@@ -53,10 +61,15 @@ __all__ = [
     "CODEBASE_VERSION",
     "DEFAULT_EPISODES_PATH",
     "DEFAULT_QUANTILES",
+    "EVENT_ONLY_STYLES",
     "EpisodeAwareSampler",
+    "LANGUAGE_EVENTS",
+    "LANGUAGE_PERSISTENT",
     "LeRobotDataset",
     "LeRobotDatasetMetadata",
     "MultiLeRobotDataset",
+    "PERSISTENT_STYLES",
+    "STYLE_REGISTRY",
     "StreamingLeRobotDataset",
     "VideoEncodingManager",
     "add_features",
@@ -66,6 +79,7 @@ __all__ = [
     "convert_image_to_video_dataset",
     "create_initial_features",
     "create_lerobot_dataset_card",
+    "column_for_style",
     "delete_episodes",
     "get_feature_stats",
     "load_episodes",

src/lerobot/datasets/compute_stats.py

@@ -512,7 +512,7 @@ def compute_episode_stats(
 
     ep_stats = {}
     for key, data in episode_data.items():
-        if features[key]["dtype"] == "string":
+        if features[key]["dtype"] in {"string", "language"}:
             continue
 
         if features[key]["dtype"] in ["image", "video"]:

src/lerobot/datasets/dataset_metadata.py

@@ -34,7 +34,6 @@ from .io_utils import (
     load_episodes,
     load_info,
     load_stats,
-    load_subtasks,
     load_tasks,
     write_info,
     write_stats,
@@ -175,7 +174,6 @@ class LeRobotDatasetMetadata:
         self.info = load_info(self.root)
         check_version_compatibility(self.repo_id, self._version, CODEBASE_VERSION)
         self.tasks = load_tasks(self.root)
-        self.subtasks = load_subtasks(self.root)
         self.episodes = load_episodes(self.root)
         self.stats = load_stats(self.root)
 
@@ -318,6 +316,39 @@ class LeRobotDatasetMetadata:
         """Keys to access visual modalities (regardless of their storage method)."""
         return [key for key, ft in self.features.items() if ft["dtype"] in ["video", "image"]]
 
+    @property
+    def has_language_columns(self) -> bool:
+        """Return ``True`` if the dataset declares any language column.
+
+        Used to gate language-aware code paths (collate, render step) so
+        unannotated datasets keep PyTorch's default collate behavior.
+        """
+        from .language import LANGUAGE_COLUMNS  # noqa: PLC0415  (avoid circular import)
+
+        return any(col in self.features for col in LANGUAGE_COLUMNS)
+
+    @property
+    def tools(self) -> list[dict]:
+        """OpenAI-style tool schemas declared by this dataset.
+
+        Read from ``meta/info.json["tools"]``. Returns a copy, so callers
+        can mutate the result safely. Falls back to
+        :data:`lerobot.datasets.language.DEFAULT_TOOLS` (the canonical
+        ``say`` schema) when the dataset doesn't declare any — that way
+        unannotated datasets and chat-template consumers
+        (``apply_chat_template(messages, tools=meta.tools)``) keep
+        working out of the box.
+
+        Implementations live under :mod:`lerobot.tools` (one file per
+        tool); see ``docs/source/tools.mdx`` for the authoring guide.
+        """
+        from .language import DEFAULT_TOOLS  # noqa: PLC0415  (avoid circular import)
+
+        declared = self.info.tools
+        if declared:
+            return [dict(t) for t in declared]
+        return [dict(t) for t in DEFAULT_TOOLS]
+
     @property
     def names(self) -> dict[str, list | dict]:
         """Names of the various dimensions of vector modalities."""
@@ -633,7 +664,6 @@ class LeRobotDatasetMetadata:
         _validate_feature_names(features)
 
         obj.tasks = None
-        obj.subtasks = None
         obj.episodes = None
         obj.stats = None
         obj.info = create_empty_dataset_info(

src/lerobot/datasets/dataset_reader.py

@@ -295,9 +295,4 @@ class DatasetReader:
         task_idx = item["task_index"].item()
         item["task"] = self._meta.tasks.iloc[task_idx].name
 
-        # add subtask information if available
-        if "subtask_index" in self._meta.features and self._meta.subtasks is not None:
-            subtask_idx = item["subtask_index"].item()
-            item["subtask"] = self._meta.subtasks.iloc[subtask_idx].name
-
         return item

src/lerobot/datasets/feature_utils.py

@@ -22,6 +22,12 @@ from PIL import Image as PILImage
 from lerobot.utils.constants import DEFAULT_FEATURES
 from lerobot.utils.utils import is_valid_numpy_dtype_string
 
+from .language import (
+    LANGUAGE_PERSISTENT,
+    is_language_column,
+    language_events_column_feature,
+    language_persistent_column_feature,
+)
 from .utils import (
     DEFAULT_CHUNK_SIZE,
     DEFAULT_DATA_FILE_SIZE_IN_MB,
@@ -46,7 +52,13 @@ def get_hf_features_from_features(features: dict) -> datasets.Features:
     """
     hf_features = {}
     for key, ft in features.items():
-        if ft["dtype"] == "video":
+        if is_language_column(key):
+            hf_features[key] = (
+                language_persistent_column_feature()
+                if key == LANGUAGE_PERSISTENT
+                else language_events_column_feature()
+            )
+        elif ft["dtype"] == "video":
             continue
         elif ft["dtype"] == "image":
             hf_features[key] = datasets.Image()
@@ -242,6 +254,8 @@ def validate_feature_dtype_and_shape(
         return validate_feature_image_or_video(name, expected_shape, value)
     elif expected_dtype == "string":
         return validate_feature_string(name, value)
+    elif expected_dtype == "language":
+        return ""
     else:
         raise NotImplementedError(f"The feature dtype '{expected_dtype}' is not implemented yet.")
 

src/lerobot/datasets/io_utils.py

@@ -31,10 +31,10 @@ from torchvision import transforms
 from lerobot.utils.io_utils import load_json, write_json
 from lerobot.utils.utils import SuppressProgressBars, flatten_dict, unflatten_dict
 
+from .language import LANGUAGE_COLUMNS
 from .utils import (
     DEFAULT_DATA_FILE_SIZE_IN_MB,
     DEFAULT_EPISODES_PATH,
-    DEFAULT_SUBTASKS_PATH,
     DEFAULT_TASKS_PATH,
     EPISODES_DIR,
     INFO_PATH,
@@ -186,14 +186,6 @@ def load_tasks(local_dir: Path) -> pandas.DataFrame:
     return tasks
 
 
-def load_subtasks(local_dir: Path) -> pandas.DataFrame | None:
-    """Load subtasks from subtasks.parquet if it exists."""
-    subtasks_path = local_dir / DEFAULT_SUBTASKS_PATH
-    if subtasks_path.exists():
-        return pd.read_parquet(subtasks_path)
-    return None
-
-
 def write_episodes(episodes: Dataset, local_dir: Path) -> None:
     """Write episode metadata to a parquet file in the LeRobot v3.0 format.
     This function writes episode-level metadata to a single parquet file.
@@ -265,11 +257,13 @@ def hf_transform_to_torch(items_dict: dict[str, list[Any]]) -> dict[str, list[to
         dict: The batch with items converted to torch tensors.
     """
     for key in items_dict:
+        if key in LANGUAGE_COLUMNS:
+            continue
         first_item = items_dict[key][0]
         if isinstance(first_item, PILImage.Image):
             to_tensor = transforms.ToTensor()
             items_dict[key] = [to_tensor(img) for img in items_dict[key]]
-        elif first_item is None:
+        elif first_item is None or isinstance(first_item, dict):
             pass
         else:
             items_dict[key] = [x if isinstance(x, str) else torch.tensor(x) for x in items_dict[key]]
@@ -304,8 +298,9 @@ def item_to_torch(item: dict) -> dict:
     Returns:
         dict: Dictionary with all tensor-like items converted to torch.Tensor.
     """
+    skip_keys = {"task", *LANGUAGE_COLUMNS}
     for key, val in item.items():
-        if isinstance(val, (np.ndarray | list)) and key not in ["task"]:
+        if isinstance(val, (np.ndarray | list)) and key not in skip_keys:
             # Convert numpy arrays and lists to torch tensors
             item[key] = torch.tensor(val)
     return item

src/lerobot/datasets/language.py

@@ -0,0 +1,240 @@
+#!/usr/bin/env python
+
+# Copyright 2026 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.
+
+from __future__ import annotations
+
+from typing import Literal
+
+import datasets
+import pyarrow as pa
+
+LANGUAGE_PERSISTENT = "language_persistent"
+LANGUAGE_EVENTS = "language_events"
+LANGUAGE_COLUMNS = (LANGUAGE_PERSISTENT, LANGUAGE_EVENTS)
+PERSISTENT_ROW_FIELDS = ("role", "content", "style", "timestamp", "camera", "tool_calls")
+EVENT_ROW_FIELDS = ("role", "content", "style", "camera", "tool_calls")
+
+CORE_STYLES = {
+    "subtask",
+    "plan",
+    "memory",
+    "motion",
+    "interjection",
+    "vqa",
+    "trace",
+    "task_aug",
+}
+# Project-local styles can be registered at import time by appending to
+# ``EXTENDED_STYLES`` before ``column_for_style`` is called. Anything added
+# here is treated as a known style alongside ``CORE_STYLES`` for resolver
+# validation. Empty by default — populate from a downstream module that
+# also extends ``PERSISTENT_STYLES`` or ``EVENT_ONLY_STYLES`` to declare
+# the new style's column.
+EXTENDED_STYLES: set[str] = set()
+STYLE_REGISTRY = CORE_STYLES | EXTENDED_STYLES
+
+PERSISTENT_STYLES = {"subtask", "plan", "memory", "motion", "task_aug"}
+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``. ``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"]
+
+
+def _json_arrow_type() -> pa.DataType:
+    """Return the Arrow JSON type, falling back to ``string`` on older pyarrow."""
+    return pa.json_() if hasattr(pa, "json_") else pa.string()
+
+
+def _json_feature() -> object:
+    """Return the HF ``datasets`` JSON feature, falling back to a string value."""
+    return datasets.Json() if hasattr(datasets, "Json") else datasets.Value("string")
+
+
+def language_persistent_row_arrow_type() -> pa.StructType:
+    """Return the Arrow struct type for a single persistent language row.
+
+    Persistent rows carry their own ``timestamp`` because they represent a state
+    that became active at a specific moment and remains active until superseded.
+    """
+    return pa.struct(
+        [
+            pa.field("role", pa.string(), nullable=False),
+            pa.field("content", pa.string(), nullable=True),
+            pa.field("style", pa.string(), nullable=True),
+            pa.field("timestamp", pa.float64(), nullable=False),
+            pa.field("camera", pa.string(), nullable=True),
+            pa.field("tool_calls", pa.list_(_json_arrow_type()), nullable=True),
+        ]
+    )
+
+
+def language_event_row_arrow_type() -> pa.StructType:
+    """Return the Arrow struct type for a single event language row.
+
+    Event rows have no ``timestamp`` field: each event is stored on the dataset
+    row whose frame timestamp is the event's firing time.
+    """
+    return pa.struct(
+        [
+            pa.field("role", pa.string(), nullable=False),
+            pa.field("content", pa.string(), nullable=True),
+            pa.field("style", pa.string(), nullable=True),
+            pa.field("camera", pa.string(), nullable=True),
+            pa.field("tool_calls", pa.list_(_json_arrow_type()), nullable=True),
+        ]
+    )
+
+
+def language_persistent_arrow_type() -> pa.ListType:
+    """Return the Arrow list type for the ``language_persistent`` column."""
+    return pa.list_(language_persistent_row_arrow_type())
+
+
+def language_events_arrow_type() -> pa.ListType:
+    """Return the Arrow list type for the ``language_events`` column."""
+    return pa.list_(language_event_row_arrow_type())
+
+
+def language_persistent_row_feature() -> dict[str, object]:
+    """Return the HF ``datasets`` feature mapping for a persistent language row."""
+    return {
+        "role": datasets.Value("string"),
+        "content": datasets.Value("string"),
+        "style": datasets.Value("string"),
+        "timestamp": datasets.Value("float64"),
+        "camera": datasets.Value("string"),
+        "tool_calls": datasets.List(_json_feature()),
+    }
+
+
+def language_event_row_feature() -> dict[str, object]:
+    """Return the HF ``datasets`` feature mapping for an event language row."""
+    return {
+        "role": datasets.Value("string"),
+        "content": datasets.Value("string"),
+        "style": datasets.Value("string"),
+        "camera": datasets.Value("string"),
+        "tool_calls": datasets.List(_json_feature()),
+    }
+
+
+def language_persistent_column_feature() -> datasets.List:
+    """Return the HF ``datasets`` feature for the ``language_persistent`` column."""
+    return datasets.List(language_persistent_row_feature())
+
+
+def language_events_column_feature() -> datasets.List:
+    """Return the HF ``datasets`` feature for the ``language_events`` column."""
+    return datasets.List(language_event_row_feature())
+
+
+def language_feature_info() -> dict[str, dict]:
+    """Return the ``info["features"]`` entries for both language columns."""
+    return {
+        LANGUAGE_PERSISTENT: {"dtype": "language", "shape": (1,), "names": None},
+        LANGUAGE_EVENTS: {"dtype": "language", "shape": (1,), "names": None},
+    }
+
+
+def is_language_column(key: str) -> bool:
+    """Return ``True`` if ``key`` is one of the dataset's language column names."""
+    return key in LANGUAGE_COLUMNS
+
+
+def is_view_dependent_style(style: str | None) -> bool:
+    """Return ``True`` if rows of ``style`` must be tagged with a ``camera`` key."""
+    return style in VIEW_DEPENDENT_STYLES
+
+
+def validate_camera_field(style: str | None, camera: str | None) -> None:
+    """Enforce the ``camera`` invariant: required iff ``style`` is view-dependent.
+
+    Raises ``ValueError`` if a view-dependent style is missing ``camera`` or if
+    a non-view-dependent style carries one. Pipeline writers and the validator
+    should call this on every emitted row.
+    """
+    if is_view_dependent_style(style):
+        if not camera:
+            raise ValueError(
+                f"Rows of view-dependent style {style!r} require a non-empty 'camera' "
+                f"field referencing an 'observation.images.*' feature key."
+            )
+    elif camera is not None:
+        raise ValueError(f"Rows of style {style!r} must have camera=None; got camera={camera!r}.")
+
+
+# --- Tool registry --------------------------------------------------------
+# Tools declared on a dataset live in ``meta/info.json["tools"]`` as a list
+# of OpenAI-style function schemas. The runtime / training stack reads them
+# through :class:`LeRobotDatasetMetadata.tools` (with these constants as
+# fallback when the dataset doesn't declare any). Implementations live
+# under :mod:`lerobot.tools` (one file per tool); see
+# ``docs/source/tools.mdx`` for the authoring guide.
+
+SAY_TOOL_SCHEMA: dict = {
+    "type": "function",
+    "function": {
+        "name": "say",
+        "description": "Speak a short utterance to the user via the TTS executor.",
+        "parameters": {
+            "type": "object",
+            "properties": {
+                "text": {
+                    "type": "string",
+                    "description": "The verbatim text to speak.",
+                }
+            },
+            "required": ["text"],
+        },
+    },
+}
+"""Canonical schema for the ``say`` tool emitted by the steerable
+annotation pipeline (PR 2 Module 2). Single source of truth — PR 2's
+writer, PR 3's runtime tool registry, and the dataset visualizer all
+import this constant rather than duplicating the dict."""
+
+DEFAULT_TOOLS: list[dict] = [SAY_TOOL_SCHEMA]
+"""Fallback tools list. Returned by ``LeRobotDatasetMetadata.tools``
+when ``meta/info.json["tools"]`` is unset, so unannotated datasets and
+chat-template consumers (``apply_chat_template(messages, tools=...)``)
+keep working out of the box."""
+
+
+def column_for_style(style: str | None) -> LanguageColumn:
+    """Map a language style to the column where rows of that style are stored.
+
+    Styles in :data:`PERSISTENT_STYLES` route to :data:`LANGUAGE_PERSISTENT`.
+    Styles in :data:`EVENT_ONLY_STYLES` and the implicit ``None`` style route
+    to :data:`LANGUAGE_EVENTS`.
+    """
+    if style is None:
+        return LANGUAGE_EVENTS
+    if style in PERSISTENT_STYLES:
+        return LANGUAGE_PERSISTENT
+    if style in EVENT_ONLY_STYLES:
+        return LANGUAGE_EVENTS
+    raise ValueError(f"Unknown language style: {style!r}")

src/lerobot/datasets/language_render.py

@@ -0,0 +1,543 @@
+#!/usr/bin/env python
+
+# Copyright 2026 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.
+
+from __future__ import annotations
+
+import copy
+import hashlib
+import re
+from collections.abc import Sequence
+from typing import Any
+
+from lerobot.configs.recipe import DEFAULT_BINDINGS, PLACEHOLDER_RE, TrainingRecipe
+
+from .language import LANGUAGE_PERSISTENT, column_for_style
+
+LanguageRow = dict[str, Any]
+RenderedMessages = dict[str, list[Any]]
+
+_RESOLVER_RE = re.compile(r"^(?P<name>[A-Za-z_][A-Za-z0-9_]*)\((?P<args>.*)\)$")
+
+
+def active_at(
+    t: float,
+    *,
+    persistent: Sequence[LanguageRow],
+    style: str | None = None,
+    role: str | None = None,
+    tool_name: str | None = None,
+    camera: str | None = None,
+) -> LanguageRow | None:
+    """Return the persistent row of ``style`` that is active at time ``t``.
+
+    A persistent row is "active" at ``t`` when its own ``timestamp`` is the
+    most recent one ``<= t`` for the given ``style``/``role``/``tool_name``/
+    ``camera`` selector. Only valid for persistent styles.
+    """
+    _validate_persistent_resolver("active_at", style)
+    matches = [
+        row
+        for row in _matching_rows(persistent, style=style, role=role, tool_name=tool_name, camera=camera)
+        if _timestamp(row) <= t
+    ]
+    if not matches:
+        return None
+    latest_ts = max(_timestamp(row) for row in matches)
+    return _select_one(
+        [row for row in matches if _timestamp(row) == latest_ts],
+        style=style,
+        role=role,
+        tool_name=tool_name,
+        camera=camera,
+    )
+
+
+EMITTED_AT_TOLERANCE_S = 0.1
+"""Half-window for matching persistent rows to a frame timestamp in
+``emitted_at``. Persistent timestamps come from parquet (float64) and ``t``
+is also a float64 from parquet, so in the ideal hot path an exact match
+would suffice — but any caller that derives ``t`` arithmetically (e.g.
+``frame_idx / fps``) breaks bit-equality. A 0.1 s tolerance covers
+common arithmetic drift without admitting frames that are visibly far
+apart at typical control rates (30–100 Hz)."""
+
+
+def emitted_at(
+    t: float,
+    *,
+    persistent: Sequence[LanguageRow],
+    events: Sequence[LanguageRow],
+    style: str | None = None,
+    role: str | None = None,
+    tool_name: str | None = None,
+    camera: str | None = None,
+) -> LanguageRow | None:
+    """Return the row of ``style`` emitted at exactly time ``t``.
+
+    For persistent styles, this matches persistent rows whose own ``timestamp``
+    is within ``EMITTED_AT_TOLERANCE_S`` of ``t`` (see that constant for why
+    we use a tolerance instead of bit-equality). For event styles, the
+    ``events`` list is assumed to come from the dataset row at frame ``t``
+    (event rows carry no timestamp of their own), so all matching event rows
+    are considered emitted at ``t``. ``camera`` filters by the row's
+    ``camera`` field — required to disambiguate when multiple view-dependent
+    rows share ``(t, role)`` across cameras.
+    """
+    if column_for_style(style) == LANGUAGE_PERSISTENT:
+        matches = [
+            row
+            for row in _matching_rows(persistent, style=style, role=role, tool_name=tool_name, camera=camera)
+            if abs(_timestamp(row) - t) <= EMITTED_AT_TOLERANCE_S
+        ]
+    else:
+        matches = _matching_rows(events, style=style, role=role, tool_name=tool_name, camera=camera)
+    return _select_one(matches, style=style, role=role, tool_name=tool_name, camera=camera)
+
+
+def nth_prev(
+    t: float,
+    *,
+    persistent: Sequence[LanguageRow],
+    style: str | None = None,
+    offset: int = 1,
+    role: str | None = None,
+    tool_name: str | None = None,
+    camera: str | None = None,
+) -> LanguageRow | None:
+    """Return the persistent row that was active ``offset`` steps before ``t``.
+
+    Walks back through chronologically sorted persistent rows of ``style``
+    (filtered by optional ``role``/``tool_name``/``camera``) and returns the
+    one ``offset`` positions before the row active at ``t``. Only valid for
+    persistent styles.
+    """
+    return _nth_relative("nth_prev", t, persistent, style, -offset, role, tool_name, camera)
+
+
+def nth_next(
+    t: float,
+    *,
+    persistent: Sequence[LanguageRow],
+    style: str | None = None,
+    offset: int = 1,
+    role: str | None = None,
+    tool_name: str | None = None,
+    camera: str | None = None,
+) -> LanguageRow | None:
+    """Return the persistent row that becomes active ``offset`` steps after ``t``.
+
+    Walks forward through chronologically sorted persistent rows of ``style``
+    (filtered by optional ``role``/``tool_name``/``camera``) and returns the
+    one ``offset`` positions after the row active at ``t``. Only valid for
+    persistent styles.
+    """
+    return _nth_relative("nth_next", t, persistent, style, offset, role, tool_name, camera)
+
+
+def render_sample(
+    *,
+    recipe: TrainingRecipe,
+    persistent: Sequence[LanguageRow] | None,
+    events: Sequence[LanguageRow] | None,
+    t: float,
+    sample_idx: int,
+    task: str | None = None,
+    dataset_ctx: Any | None = None,
+) -> RenderedMessages | None:
+    """Render the chat-style messages for a single dataset sample.
+
+    Resolves the recipe's bindings against ``persistent`` and ``events`` rows
+    at frame timestamp ``t``, then expands the recipe's message templates.
+    Returns ``None`` if the resolved sample contains no target message.
+    """
+    persistent_rows = _normalize_rows(persistent or [])
+    event_rows = _normalize_rows(events or [])
+    selected_recipe = _select_recipe(recipe, sample_idx)
+    bindings = _resolve_bindings(
+        selected_recipe,
+        persistent=persistent_rows,
+        events=event_rows,
+        t=t,
+        sample_idx=sample_idx,
+        task=task,
+        dataset_ctx=dataset_ctx,
+    )
+    return _render_message_recipe(selected_recipe, bindings)
+
+
+def _select_recipe(recipe: TrainingRecipe, sample_idx: int) -> TrainingRecipe:
+    """Pick a deterministic blend component for ``sample_idx`` (or return ``recipe``)."""
+    if recipe.blend is None:
+        return recipe
+
+    total_weight = sum(component.weight or 0.0 for component in recipe.blend.values())
+    if total_weight <= 0:
+        raise ValueError("Blend weights must sum to a positive value.")
+
+    digest = hashlib.blake2b(str(sample_idx).encode(), digest_size=8).digest()
+    draw = int.from_bytes(digest, "big") / 2**64 * total_weight
+    cumulative = 0.0
+    last_component: TrainingRecipe | None = None
+    for component in recipe.blend.values():
+        last_component = component
+        cumulative += component.weight or 0.0
+        if draw < cumulative:
+            return component
+    assert last_component is not None
+    return last_component
+
+
+def _resolve_bindings(
+    recipe: TrainingRecipe,
+    *,
+    persistent: Sequence[LanguageRow],
+    events: Sequence[LanguageRow],
+    t: float,
+    sample_idx: int,
+    task: str | None,
+    dataset_ctx: Any | None,
+) -> dict[str, LanguageRow | str | None]:
+    """Resolve every binding in ``recipe`` (plus ``task``) at time ``t``."""
+    bindings: dict[str, LanguageRow | str | None] = {
+        "task": _resolve_task(task, dataset_ctx, persistent=persistent, sample_idx=sample_idx),
+    }
+    specs = {**DEFAULT_BINDINGS, **(recipe.bindings or {})}
+    for name, spec in specs.items():
+        bindings[name] = _resolve_spec(spec, persistent=persistent, events=events, t=t)
+    return bindings
+
+
+def _resolve_task(
+    task: str | None,
+    dataset_ctx: Any | None,
+    *,
+    persistent: Sequence[LanguageRow] = (),
+    sample_idx: int = 0,
+) -> str | None:
+    """Return the task string for ``sample_idx``.
+
+    Resolution order:
+
+    1. Explicit ``task`` override (caller-supplied) wins.
+    2. If ``persistent`` contains rows of style ``task_aug`` (role=user),
+       deterministically pick one by ``sample_idx`` so each frame of an
+       episode rotates through the available rephrasings across an epoch.
+       This realizes Xiao 2022 / CAST-style task-prompt diversity without
+       changing ``meta/tasks.parquet`` and without forcing recipes to opt
+       in: ``${task}`` automatically picks a rephrasing when one exists,
+       and falls back to the canonical task otherwise. Recipes that want
+       the literal canonical task can override the binding.
+    3. Otherwise read the canonical task from ``dataset_ctx`` (which is
+       backed by ``meta/tasks.parquet``).
+    """
+    if task is not None:
+        return task
+
+    aug_rows = [r for r in persistent if r.get("style") == "task_aug" and r.get("role") == "user"]
+    if aug_rows:
+        # Deterministic, blake2b-based pick keyed on sample_idx so the
+        # rotation is reproducible across runs (Python's built-in ``hash``
+        # is process-randomized).
+        digest = hashlib.blake2b(f"task_aug:{sample_idx}".encode(), digest_size=8).digest()
+        idx = int.from_bytes(digest, "big") % len(aug_rows)
+        chosen = aug_rows[idx].get("content")
+        if chosen:
+            return str(chosen)
+
+    if dataset_ctx is None:
+        return None
+    if isinstance(dataset_ctx, dict):
+        return dataset_ctx.get("task")
+    return getattr(dataset_ctx, "task", None)
+
+
+def _resolve_spec(
+    spec: str,
+    *,
+    persistent: Sequence[LanguageRow],
+    events: Sequence[LanguageRow],
+    t: float,
+) -> LanguageRow | None:
+    """Parse a single binding's resolver expression and dispatch to its function."""
+    match = _RESOLVER_RE.match(spec.strip())
+    if match is None:
+        raise ValueError(f"Invalid resolver expression: {spec!r}")
+    name = match.group("name")
+    kwargs = _parse_resolver_args(match.group("args"))
+    kwargs.pop("t_arg", None)
+
+    if name == "emitted_at":
+        return emitted_at(t, persistent=persistent, events=events, **kwargs)
+    if name == "active_at":
+        return active_at(t, persistent=persistent, **kwargs)
+    if name == "nth_prev":
+        return nth_prev(t, persistent=persistent, **kwargs)
+    if name == "nth_next":
+        return nth_next(t, persistent=persistent, **kwargs)
+    raise ValueError(f"Unknown language resolver: {name!r}")
+
+
+def _parse_resolver_args(args: str) -> dict[str, Any]:
+    """Parse a comma-separated resolver argument list into a kwargs dict."""
+    kwargs: dict[str, Any] = {}
+    if not args.strip():
+        return kwargs
+
+    parts = [part.strip() for part in args.split(",") if part.strip()]
+    for part in parts:
+        if part == "t":
+            kwargs["t_arg"] = True
+            continue
+        if "=" not in part:
+            raise ValueError(f"Invalid resolver argument: {part!r}")
+        key, value = (item.strip() for item in part.split("=", 1))
+        if key == "offset":
+            kwargs[key] = int(value)
+        else:
+            kwargs[key] = value.strip("\"'")
+    return kwargs
+
+
+def _render_message_recipe(
+    recipe: TrainingRecipe,
+    bindings: dict[str, LanguageRow | str | None],
+) -> RenderedMessages | None:
+    """Expand ``recipe.messages`` into rendered chat messages using ``bindings``."""
+    assert recipe.messages is not None
+    messages: list[dict[str, Any]] = []
+    streams: list[str | None] = []
+    target_indices: list[int] = []
+
+    for turn in recipe.messages:
+        if turn.if_present is not None and bindings.get(turn.if_present) is None:
+            continue
+
+        message = {"role": turn.role}
+        if turn.content is not None:
+            message["content"] = _render_content(turn.content, bindings)
+
+        if turn.tool_calls_from is not None:
+            row = bindings.get(turn.tool_calls_from)
+            tool_calls = row.get("tool_calls") if isinstance(row, dict) else None
+            if tool_calls:
+                message["tool_calls"] = copy.deepcopy(tool_calls)
+
+        message_idx = len(messages)
+        messages.append(message)
+        streams.append(turn.stream)
+        if turn.target:
+            target_indices.append(message_idx)
+
+    if not target_indices:
+        return None
+
+    rendered = {
+        "messages": messages,
+        "message_streams": streams,
+        "target_message_indices": target_indices,
+    }
+    _validate_rendered(rendered)
+    return rendered
+
+
+def _render_content(
+    content: str | list[dict[str, Any]],
+    bindings: dict[str, LanguageRow | str | None],
+) -> str | list[dict[str, Any]]:
+    """Substitute bindings into a string or each string field of multimodal blocks."""
+    if isinstance(content, str):
+        return _substitute(content, bindings)
+
+    rendered_blocks = []
+    for block in content:
+        rendered_block = copy.deepcopy(block)
+        for key, value in rendered_block.items():
+            if isinstance(value, str):
+                rendered_block[key] = _substitute(value, bindings)
+        rendered_blocks.append(rendered_block)
+    return rendered_blocks
+
+
+def _substitute(template: str, bindings: dict[str, LanguageRow | str | None]) -> str:
+    """Replace ``${name}`` placeholders in ``template`` with their bound values."""
+
+    def replace(match: re.Match[str]) -> str:
+        """Resolve a single ``${name}`` match to its bound string value."""
+        name = match.group(1)
+        if name not in bindings:
+            raise ValueError(f"Unknown template binding: {name!r}")
+        value = bindings[name]
+        if value is None:
+            return ""
+        if isinstance(value, dict):
+            content = value.get("content")
+            return "" if content is None else str(content)
+        return str(value)
+
+    return PLACEHOLDER_RE.sub(replace, template)
+
+
+def _validate_rendered(rendered: RenderedMessages) -> None:
+    """Sanity-check the rendered output for stream/target alignment."""
+    messages = rendered["messages"]
+    streams = rendered["message_streams"]
+    target_indices = rendered["target_message_indices"]
+
+    if len(streams) != len(messages):
+        raise ValueError("message_streams must be aligned with messages.")
+    if not target_indices:
+        raise ValueError("Rendered samples must contain at least one target message.")
+    for idx in target_indices:
+        if idx < 0 or idx >= len(messages):
+            raise ValueError(f"Target message index {idx} is out of bounds.")
+    # ``stream`` is enforced non-None at MessageTurn construction time
+    # (see ``MessageTurn.__post_init__``), so a missing stream here would
+    # mean the dataclass invariant was bypassed; no need to re-check.
+
+
+def _nth_relative(
+    name: str,
+    t: float,
+    persistent: Sequence[LanguageRow],
+    style: str | None,
+    offset: int,
+    role: str | None,
+    tool_name: str | None,
+    camera: str | None,
+) -> LanguageRow | None:
+    """Shared body for ``nth_prev`` / ``nth_next`` with signed ``offset``."""
+    _validate_persistent_resolver(name, style)
+    if abs(offset) < 1:
+        raise ValueError(f"{name} offset must be non-zero.")
+
+    rows = sorted(
+        _matching_rows(persistent, style=style, role=role, tool_name=tool_name, camera=camera),
+        key=_row_sort_key,
+    )
+    if not rows:
+        return None
+
+    anchor_idx = None
+    for idx, row in enumerate(rows):
+        if _timestamp(row) <= t:
+            anchor_idx = idx
+        else:
+            break
+
+    target_idx = (offset - 1 if offset > 0 else None) if anchor_idx is None else anchor_idx + offset
+
+    if target_idx is None or target_idx < 0 or target_idx >= len(rows):
+        return None
+    return rows[target_idx]
+
+
+def _validate_persistent_resolver(name: str, style: str | None) -> None:
+    """Reject calls with missing or event-only ``style`` for persistent resolvers."""
+    if style is None:
+        raise ValueError(f"{name} requires a persistent style.")
+    if column_for_style(style) != LANGUAGE_PERSISTENT:
+        raise ValueError(f"{name} cannot be used with event-only style {style!r}.")
+
+
+def _matching_rows(
+    rows: Sequence[LanguageRow],
+    *,
+    style: str | None,
+    role: str | None,
+    tool_name: str | None,
+    camera: str | None,
+) -> list[LanguageRow]:
+    """Return ``rows`` filtered by optional ``style``/``role``/``tool_name``/``camera`` selectors."""
+    return [
+        row
+        for row in rows
+        if (style is None or row.get("style") == style)
+        and (role is None or row.get("role") == role)
+        and (tool_name is None or _row_has_tool_name(row, tool_name))
+        and (camera is None or row.get("camera") == camera)
+    ]
+
+
+def _select_one(
+    rows: Sequence[LanguageRow],
+    *,
+    style: str | None,
+    role: str | None,
+    tool_name: str | None,
+    camera: str | None,
+) -> LanguageRow | None:
+    """Return the single matching row, or raise if the resolver is ambiguous.
+
+    Multiple matches always raise — even when the caller already passed
+    some selectors — because remaining ambiguity means the data has
+    several rows that look identical to the resolver and the caller
+    needs to pin down a specific one (e.g. add ``camera=...`` for VQA
+    rows shared across cameras).
+    """
+    if not rows:
+        return None
+    if len(rows) > 1:
+        raise ValueError(
+            f"Ambiguous resolver for style={style!r} role={role!r} "
+            f"tool_name={tool_name!r} camera={camera!r}: {len(rows)} matching rows. "
+            f"Add a selector that distinguishes them."
+        )
+    return rows[0]
+
+
+def _row_sort_key(row: LanguageRow) -> tuple[float, str, str]:
+    """Stable sort key for both persistent and event rows.
+
+    Event rows lack ``timestamp`` (it is implicit in the frame), so default
+    to ``0.0`` — within a single frame all event rows share the same sort
+    bucket and are tiebroken by ``(style, role)``.
+    """
+    timestamp = row.get("timestamp")
+    ts = (
+        float(timestamp.item() if hasattr(timestamp, "item") else timestamp) if timestamp is not None else 0.0
+    )
+    return (ts, row.get("style") or "", row.get("role") or "")
+
+
+def _timestamp(row: LanguageRow) -> float:
+    """Extract a row's ``timestamp`` as a Python float (unwrapping numpy scalars)."""
+    value = row["timestamp"]
+    return float(value.item() if hasattr(value, "item") else value)
+
+
+def _row_has_tool_name(row: LanguageRow, tool_name: str) -> bool:
+    """Return ``True`` if any of the row's tool calls invokes ``tool_name``."""
+    for tool_call in row.get("tool_calls") or []:
+        if isinstance(tool_call, str):
+            continue
+        function = tool_call.get("function") if isinstance(tool_call, dict) else None
+        if isinstance(function, dict) and function.get("name") == tool_name:
+            return True
+    return False
+
+
+def _normalize_rows(rows: Sequence[Any]) -> list[LanguageRow]:
+    """Convert pyarrow scalars / mappings into a fresh list of plain dict rows."""
+    normalized = []
+    for row in rows:
+        if row is None:
+            continue
+        if hasattr(row, "as_py"):
+            row = row.as_py()
+        if not isinstance(row, dict):
+            raise TypeError(f"Language rows must be dictionaries, got {type(row).__name__}.")
+        normalized.append(dict(row))
+    return normalized

src/lerobot/datasets/utils.py

@@ -88,7 +88,6 @@ VIDEO_DIR = "videos"
 
 CHUNK_FILE_PATTERN = "chunk-{chunk_index:03d}/file-{file_index:03d}"
 DEFAULT_TASKS_PATH = "meta/tasks.parquet"
-DEFAULT_SUBTASKS_PATH = "meta/subtasks.parquet"
 DEFAULT_EPISODES_PATH = EPISODES_DIR + "/" + CHUNK_FILE_PATTERN + ".parquet"
 DEFAULT_DATA_PATH = DATA_DIR + "/" + CHUNK_FILE_PATTERN + ".parquet"
 DEFAULT_VIDEO_PATH = VIDEO_DIR + "/{video_key}/" + CHUNK_FILE_PATTERN + ".mp4"
@@ -130,6 +129,9 @@ class DatasetInfo:
     # Optional metadata
     robot_type: str | None = None
     splits: dict[str, str] = field(default_factory=dict)
+    # OpenAI-style tool schemas declared by the dataset. ``None`` means the
+    # dataset doesn't declare any — readers fall back to ``DEFAULT_TOOLS``.
+    tools: list[dict] | None = None
 
     def __post_init__(self) -> None:
         # Coerce feature shapes from list to tuple — JSON deserialisation
@@ -151,11 +153,15 @@ class DatasetInfo:
         """Return a JSON-serialisable dict.
 
         Converts tuple shapes back to lists so ``json.dump`` can handle them.
+        Drops ``tools`` when unset so existing datasets keep a clean
+        ``info.json``.
         """
         d = dataclasses.asdict(self)
         for ft in d["features"].values():
             if isinstance(ft.get("shape"), tuple):
                 ft["shape"] = list(ft["shape"])
+        if d.get("tools") is None:
+            d.pop("tools", None)
         return d
 
     @classmethod

src/lerobot/datasets/video_utils.py

@@ -282,11 +282,7 @@ class VideoDecoderCache:
         with self._lock:
             if video_path not in self._cache:
                 file_handle = fsspec.open(video_path).__enter__()
-                try:
-                    decoder = VideoDecoder(file_handle, seek_mode="approximate")
-                except Exception:
-                    file_handle.close()
-                    raise
+                decoder = VideoDecoder(file_handle, seek_mode="approximate")
                 self._cache[video_path] = (decoder, file_handle)
 
             return self._cache[video_path][0]

src/lerobot/policies/wall_x/qwen_model/qwen2_5_vl_moe.py

@@ -939,7 +939,7 @@ class Qwen2_5_VLFlashAttention2(Qwen2_5_VLAttention):
         input_dtype = query_states.dtype
         if input_dtype == torch.float32:
             if torch.is_autocast_enabled():
-                target_dtype = torch.get_autocast_dtype(query_states.device.type)
+                target_dtype = torch.get_autocast_gpu_dtype()
             # Handle the case where the model is quantized
             elif hasattr(self.config, "_pre_quantization_dtype"):
                 target_dtype = self.config._pre_quantization_dtype

src/lerobot/policies/xvla/modeling_florence2.py

@@ -985,7 +985,7 @@ class Florence2FlashAttention2(Florence2Attention):
         input_dtype = query_states.dtype
         if input_dtype == torch.float32:
             if torch.is_autocast_enabled():
-                target_dtype = torch.get_autocast_dtype(query_states.device.type)
+                target_dtype = torch.get_autocast_gpu_dtype()
             # Handle the case where the model is quantized
             elif hasattr(self.config, "_pre_quantization_dtype"):
                 target_dtype = self.config._pre_quantization_dtype

src/lerobot/processor/__init__.py

@@ -95,6 +95,13 @@ from .relative_action_processor import (
 from .rename_processor import RenameObservationsProcessorStep, rename_stats
 from .tokenizer_processor import ActionTokenizerProcessorStep, TokenizerProcessorStep
 
+# RenderMessagesStep is intentionally NOT re-exported here: it pulls in
+# `lerobot.datasets.language`, which requires the `[dataset]` extra
+# (`datasets`, `pyarrow`). Importing it from the processor package would
+# break every base-install consumer of `lerobot.processor`. Users that
+# need it import directly:
+#   from lerobot.processor.render_messages_processor import RenderMessagesStep
+
 __all__ = [
     "ActionProcessorStep",
     "AddTeleopActionAsComplimentaryDataStep",

src/lerobot/processor/batch_processor.py

@@ -174,6 +174,24 @@ class AddBatchDimensionComplementaryDataStep(ComplementaryDataProcessorStep):
             task_index_value = complementary_data["task_index"]
             if isinstance(task_index_value, Tensor) and task_index_value.dim() == 0:
                 complementary_data["task_index"] = task_index_value.unsqueeze(0)
+
+        complementary_data.pop("language_persistent", None)
+        complementary_data.pop("language_events", None)
+
+        if "messages" in complementary_data:
+            messages = complementary_data["messages"]
+            if isinstance(messages, list) and (not messages or isinstance(messages[0], dict)):
+                complementary_data["messages"] = [messages]
+
+        if "message_streams" in complementary_data:
+            streams = complementary_data["message_streams"]
+            if isinstance(streams, list) and (not streams or isinstance(streams[0], str)):
+                complementary_data["message_streams"] = [streams]
+
+        if "target_message_indices" in complementary_data:
+            indices = complementary_data["target_message_indices"]
+            if isinstance(indices, list) and (not indices or isinstance(indices[0], int)):
+                complementary_data["target_message_indices"] = [indices]
         return complementary_data
 
     def transform_features(

src/lerobot/processor/converters.py

@@ -153,26 +153,30 @@ def from_tensor_to_numpy(x: torch.Tensor | Any) -> np.ndarray | float | int | An
     return x
 
 
+_COMPLEMENTARY_KEYS = (
+    "task",
+    "index",
+    "task_index",
+    "episode_index",
+    "timestamp",
+    "language_persistent",
+    "language_events",
+    "messages",
+    "message_streams",
+    "target_message_indices",
+)
+
+
 def _extract_complementary_data(batch: dict[str, Any]) -> dict[str, Any]:
-    """
-    Extract complementary data from a batch dictionary.
+    """Extract complementary data from a batch dictionary.
 
-    This includes padding flags, task description, and indices.
-
-    Args:
-        batch: The batch dictionary.
-
-    Returns:
-        A dictionary with the extracted complementary data.
+    Includes padding flags (any key containing ``_is_pad``) plus the fixed
+    set of metadata / language keys defined in ``_COMPLEMENTARY_KEYS`` —
+    each only when present in ``batch``.
     """
     pad_keys = {k: v for k, v in batch.items() if "_is_pad" in k}
-    task_key = {"task": batch["task"]} if "task" in batch else {}
-    subtask_key = {"subtask": batch["subtask"]} if "subtask" in batch else {}
-    index_key = {"index": batch["index"]} if "index" in batch else {}
-    task_index_key = {"task_index": batch["task_index"]} if "task_index" in batch else {}
-    episode_index_key = {"episode_index": batch["episode_index"]} if "episode_index" in batch else {}
-
-    return {**pad_keys, **task_key, **subtask_key, **index_key, **task_index_key, **episode_index_key}
+    extras = {k: batch[k] for k in _COMPLEMENTARY_KEYS if k in batch}
+    return {**pad_keys, **extras}
 
 
 def create_transition(

src/lerobot/processor/render_messages_processor.py

@@ -0,0 +1,94 @@
+#!/usr/bin/env python
+
+# Copyright 2026 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.
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Any
+
+from lerobot.configs import PipelineFeatureType, PolicyFeature
+from lerobot.configs.recipe import TrainingRecipe
+from lerobot.datasets.language import LANGUAGE_EVENTS, LANGUAGE_PERSISTENT
+from lerobot.datasets.language_render import render_sample
+from lerobot.types import EnvTransition, TransitionKey
+
+from .pipeline import ProcessorStep, ProcessorStepRegistry
+
+
+@dataclass
+@ProcessorStepRegistry.register(name="render_messages_processor")
+class RenderMessagesStep(ProcessorStep):
+    """Processor step that turns raw language columns into rendered chat messages.
+
+    Reads ``language_persistent`` and ``language_events`` from the transition's
+    complementary data, renders them through ``recipe`` at the sample timestamp,
+    and replaces the raw columns with the resulting ``messages`` /
+    ``message_streams`` / ``target_message_indices`` keys.
+    """
+
+    recipe: TrainingRecipe
+    dataset_ctx: Any | None = None
+
+    def __call__(self, transition: EnvTransition) -> EnvTransition | None:
+        """Render messages for a single transition; return ``None`` to drop it."""
+        complementary_data = transition.get(TransitionKey.COMPLEMENTARY_DATA) or {}
+        persistent = complementary_data.get(LANGUAGE_PERSISTENT) or []
+        events = complementary_data.get(LANGUAGE_EVENTS) or []
+
+        if not persistent and not events:
+            return transition
+
+        timestamp = complementary_data.get("timestamp")
+        if timestamp is None:
+            raise KeyError("RenderMessagesStep requires sample timestamp in complementary data.")
+
+        sample_idx = complementary_data.get("index", 0)
+        rendered = render_sample(
+            recipe=self.recipe,
+            persistent=persistent,
+            events=events,
+            t=_scalar(timestamp),
+            sample_idx=int(_scalar(sample_idx)),
+            task=complementary_data.get("task"),
+            dataset_ctx=self.dataset_ctx,
+        )
+        if rendered is None:
+            return None
+
+        new_transition = transition.copy()
+        new_complementary_data = dict(complementary_data)
+        new_complementary_data.pop(LANGUAGE_PERSISTENT, None)
+        new_complementary_data.pop(LANGUAGE_EVENTS, None)
+        new_complementary_data.update(rendered)
+        new_transition[TransitionKey.COMPLEMENTARY_DATA] = new_complementary_data
+        return new_transition
+
+    def transform_features(
+        self, features: dict[PipelineFeatureType, dict[str, PolicyFeature]]
+    ) -> dict[PipelineFeatureType, dict[str, PolicyFeature]]:
+        """Pass features through unchanged; rendering only touches complementary data."""
+        return features
+
+
+def _scalar(value: Any) -> float | int:
+    """Unwrap a tensor/array/single-element list into a Python scalar."""
+    if hasattr(value, "item"):
+        return value.item()
+    if isinstance(value, list):
+        if len(value) != 1:
+            raise ValueError(f"Expected a scalar, got list of length {len(value)}: {value!r}")
+        return _scalar(value[0])
+    return value

src/lerobot/scripts/lerobot_train.py

@@ -48,6 +48,7 @@ from lerobot.envs import close_envs, make_env, make_env_pre_post_processors
 from lerobot.optim.factory import make_optimizer_and_scheduler
 from lerobot.policies import PreTrainedPolicy, make_policy, make_pre_post_processors
 from lerobot.rewards import make_reward_pre_post_processors
+from lerobot.utils.collate import lerobot_collate_fn
 from lerobot.utils.import_utils import register_third_party_plugins
 from lerobot.utils.logging_utils import AverageMeter, MetricsTracker
 from lerobot.utils.random_utils import set_seed
@@ -401,6 +402,10 @@ def train(cfg: TrainPipelineConfig, accelerator: "Accelerator | None" = None):
         shuffle = True
         sampler = None
 
+    # Only swap in the language-aware collate when the dataset actually
+    # declares language columns; otherwise stay on PyTorch's default
+    # collate so non-language training runs are unaffected.
+    collate_fn = lerobot_collate_fn if dataset.meta.has_language_columns else None
     dataloader = torch.utils.data.DataLoader(
         dataset,
         num_workers=cfg.num_workers,
@@ -409,6 +414,7 @@ def train(cfg: TrainPipelineConfig, accelerator: "Accelerator | None" = None):
         sampler=sampler,
         pin_memory=device.type == "cuda",
         drop_last=False,
+        collate_fn=collate_fn,
         prefetch_factor=cfg.prefetch_factor if cfg.num_workers > 0 else None,
         persistent_workers=cfg.persistent_workers and cfg.num_workers > 0,
     )

src/lerobot/utils/collate.py

@@ -0,0 +1,65 @@
+#!/usr/bin/env python
+
+# Copyright 2026 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.
+
+from __future__ import annotations
+
+from typing import Any
+
+from torch.utils.data._utils.collate import default_collate
+
+from lerobot.datasets.language import LANGUAGE_COLUMNS
+
+_PYTHON_LIST_KEYS = {"messages", "message_streams", "target_message_indices"}
+
+
+def lerobot_collate_fn(batch: list[dict[str, Any] | None]) -> dict[str, Any] | None:
+    """Collate function that preserves Python-list and language fields as lists.
+
+    Drops ``None`` samples (e.g. recipes that yielded no target message), keeps
+    rendered-message and language fields as plain Python lists, and delegates
+    every other key to PyTorch's ``default_collate``.
+    """
+    batch = [sample for sample in batch if sample is not None]
+    if not batch:
+        return None
+
+    # All-or-nothing per key: a partial-presence batch (e.g. half the samples
+    # carry `messages` and half don't) is a real bug in the upstream
+    # rendering step — silently filtering would hand downstream consumers a
+    # preserved list shorter than the tensor batch. Raise instead so the
+    # mismatch surfaces at the boundary.
+    preserved: dict[str, list[Any]] = {}
+    for key in _PYTHON_LIST_KEYS:
+        presence = [key in sample for sample in batch]
+        if not any(presence):
+            continue
+        if not all(presence):
+            raise ValueError(
+                f"Inconsistent batch: {sum(presence)}/{len(batch)} samples carry {key!r}; "
+                f"every sample in a batch must agree."
+            )
+        preserved[key] = [sample[key] for sample in batch]
+    tensorizable = [
+        {
+            key: value
+            for key, value in sample.items()
+            if key not in _PYTHON_LIST_KEYS and key not in LANGUAGE_COLUMNS
+        }
+        for sample in batch
+    ]
+    collated = default_collate(tensorizable)
+    collated.update(preserved)
+    return collated

tests/configs/test_recipe.py

@@ -0,0 +1,168 @@
+#!/usr/bin/env python
+
+from pathlib import Path
+from textwrap import dedent
+
+import pytest
+
+from lerobot.configs.recipe import MessageTurn, TrainingRecipe, load_recipe
+
+
+def _minimal_message_turn(content: str = "${task}") -> MessageTurn:
+    return MessageTurn(role="user", content=content, stream="high_level")
+
+
+def _minimal_target_turn() -> MessageTurn:
+    return MessageTurn(role="assistant", content="ok", stream="high_level", target=True)
+
+
+# ── Message-recipe validation ────────────────────────────────────────
+
+
+def test_message_recipe_validates_unknown_binding():
+    with pytest.raises(ValueError, match="unknown binding"):
+        TrainingRecipe(
+            messages=[
+                MessageTurn(role="user", content="${missing}", stream="high_level"),
+                _minimal_target_turn(),
+            ]
+        )
+
+
+def test_message_turn_requires_a_stream():
+    """Every turn must declare a stream — None is rejected at construction.
+
+    Previously this only failed at render time (``_validate_rendered``);
+    catching it here means a malformed recipe YAML errors at load instead
+    of at the first training sample.
+    """
+    with pytest.raises(ValueError, match="missing a stream"):
+        MessageTurn(role="user", content="${task}")
+
+
+def test_message_recipe_requires_at_least_one_target():
+    with pytest.raises(ValueError, match="target"):
+        TrainingRecipe(
+            messages=[
+                _minimal_message_turn(),
+                MessageTurn(role="assistant", content="no target", stream="high_level"),
+            ]
+        )
+
+
+def test_recipe_rejects_both_messages_and_blend():
+    with pytest.raises(ValueError, match="only one"):
+        TrainingRecipe(
+            messages=[_minimal_message_turn(), _minimal_target_turn()],
+            blend={"a": TrainingRecipe(weight=1.0, messages=[_minimal_target_turn()])},
+        )
+
+
+def test_recipe_rejects_neither_messages_nor_blend():
+    with pytest.raises(ValueError, match="must set one"):
+        TrainingRecipe()
+
+
+# ── Blend validation ─────────────────────────────────────────────────
+
+
+def test_blend_must_be_non_empty():
+    with pytest.raises(ValueError, match="at least one component"):
+        TrainingRecipe(blend={})
+
+
+def test_blend_component_must_define_weight():
+    with pytest.raises(ValueError, match="weight"):
+        TrainingRecipe(blend={"a": TrainingRecipe(messages=[_minimal_target_turn()])})
+
+
+def test_blend_component_weight_must_be_positive():
+    with pytest.raises(ValueError, match="positive weight"):
+        TrainingRecipe(blend={"a": TrainingRecipe(weight=0.0, messages=[_minimal_target_turn()])})
+
+
+def test_blend_component_must_define_messages():
+    # A bare TrainingRecipe(weight=1.0) would itself raise; build it without
+    # going through __post_init__ to exercise the blend-level validator.
+    bad = TrainingRecipe.__new__(TrainingRecipe)
+    bad.messages = None
+    bad.bindings = None
+    bad.blend = None
+    bad.weight = 1.0
+    with pytest.raises(ValueError, match="must define messages"):
+        TrainingRecipe(blend={"a": bad})
+
+
+def test_blend_components_cannot_themselves_define_a_blend():
+    inner = TrainingRecipe(blend={"x": TrainingRecipe(weight=1.0, messages=[_minimal_target_turn()])})
+    # Force-bypass the inner component's normal validation so the test
+    # exercises the outer blend's "no nested blends" rule directly.
+    nested = TrainingRecipe.__new__(TrainingRecipe)
+    nested.messages = None
+    nested.bindings = None
+    nested.blend = inner.blend
+    nested.weight = 1.0
+    with pytest.raises(ValueError, match="cannot itself define a blend"):
+        TrainingRecipe(blend={"outer": nested})
+
+
+# ── from_dict / from_yaml round-trips ────────────────────────────────
+
+
+def test_from_dict_with_nested_blend():
+    recipe = TrainingRecipe.from_dict(
+        {
+            "blend": {
+                "a": {
+                    "weight": 1.0,
+                    "messages": [
+                        {"role": "user", "content": "${task}", "stream": "high_level"},
+                        {"role": "assistant", "content": "a", "stream": "high_level", "target": True},
+                    ],
+                },
+                "b": {
+                    "weight": 2.0,
+                    "messages": [
+                        {"role": "user", "content": "${task}", "stream": "high_level"},
+                        {"role": "assistant", "content": "b", "stream": "high_level", "target": True},
+                    ],
+                },
+            }
+        }
+    )
+    assert recipe.blend is not None
+    assert set(recipe.blend) == {"a", "b"}
+    assert recipe.blend["b"].weight == 2.0
+    # Inner messages were promoted to MessageTurn instances.
+    assert isinstance(recipe.blend["a"].messages[0], MessageTurn)
+
+
+def test_from_yaml_round_trips_through_load_recipe(tmp_path: Path):
+    yaml_text = dedent(
+        """
+        bindings:
+          custom: "active_at(t, style=subtask)"
+        messages:
+          - {role: user, content: "${task}: ${custom}", stream: high_level}
+          - {role: assistant, content: "ok", stream: high_level, target: true}
+        """
+    ).strip()
+    path = tmp_path / "recipe.yaml"
+    path.write_text(yaml_text)
+
+    via_classmethod = TrainingRecipe.from_yaml(path)
+    via_helper = load_recipe(path)
+
+    assert via_classmethod.bindings == {"custom": "active_at(t, style=subtask)"}
+    assert via_classmethod.messages[1].target is True
+    # ``load_recipe`` is just a wrapper, but assert the two paths agree
+    # on the structural result so a future divergence is caught here.
+    assert via_helper.bindings == via_classmethod.bindings
+    assert len(via_helper.messages) == len(via_classmethod.messages)
+
+
+def test_from_yaml_rejects_non_mapping(tmp_path: Path):
+    path = tmp_path / "bad.yaml"
+    path.write_text("- just\n- a\n- list\n")
+    with pytest.raises(ValueError, match="mapping at the top level"):
+        TrainingRecipe.from_yaml(path)

tests/datasets/test_dataset_metadata.py

@@ -385,3 +385,84 @@ def test_finalize_flushes_buffered_metadata(tmp_path):
     assert episodes_dir.exists()
     parquet_files = list(episodes_dir.rglob("*.parquet"))
     assert len(parquet_files) > 0
+
+
+# ── Tools accessor ───────────────────────────────────────────────────
+
+
+def test_tools_falls_back_to_default_when_info_has_no_tools_field(tmp_path):
+    """meta.tools returns DEFAULT_TOOLS when info.json doesn't declare any."""
+    from lerobot.datasets.language import DEFAULT_TOOLS
+
+    root = tmp_path / "no_tools"
+    meta = LeRobotDatasetMetadata.create(
+        repo_id="test/no_tools",
+        fps=DEFAULT_FPS,
+        features=SIMPLE_FEATURES,
+        root=root,
+        use_videos=False,
+    )
+
+    assert meta.tools == DEFAULT_TOOLS
+    # info.json on disk should NOT include a `tools` key for clean datasets
+    with open(root / INFO_PATH) as f:
+        info_on_disk = json.load(f)
+    assert "tools" not in info_on_disk
+
+
+def test_tools_reads_declared_tools_from_info_json(tmp_path):
+    """A `tools` list written into info.json survives load → meta.tools.
+
+    Regression test for the bug where ``DatasetInfo.from_dict`` silently
+    dropped the ``tools`` key (no matching dataclass field), so
+    ``meta.tools`` always returned ``DEFAULT_TOOLS`` regardless of
+    what was on disk.
+    """
+    from lerobot.datasets.io_utils import load_info
+
+    root = tmp_path / "with_tools"
+    meta = LeRobotDatasetMetadata.create(
+        repo_id="test/with_tools",
+        fps=DEFAULT_FPS,
+        features=SIMPLE_FEATURES,
+        root=root,
+        use_videos=False,
+    )
+
+    custom_tool = {
+        "type": "function",
+        "function": {
+            "name": "record_observation",
+            "description": "Capture a still image.",
+            "parameters": {
+                "type": "object",
+                "properties": {"label": {"type": "string"}},
+                "required": ["label"],
+            },
+        },
+    }
+    info_path = root / INFO_PATH
+    with open(info_path) as f:
+        raw = json.load(f)
+    raw["tools"] = [custom_tool]
+    with open(info_path, "w") as f:
+        json.dump(raw, f)
+
+    # Reload info from disk and rebind it on the metadata object
+    meta.info = load_info(root)
+    assert meta.tools == [custom_tool]
+
+
+def test_tools_round_trip_through_dataset_info(tmp_path):
+    """A `tools` list survives DatasetInfo.from_dict / to_dict."""
+    from lerobot.datasets.utils import DatasetInfo
+
+    raw = {
+        "codebase_version": "v3.1",
+        "fps": 30,
+        "features": SIMPLE_FEATURES,
+        "tools": [{"type": "function", "function": {"name": "say"}}],
+    }
+    info = DatasetInfo.from_dict(raw)
+    assert info.tools == raw["tools"]
+    assert info.to_dict()["tools"] == raw["tools"]

tests/datasets/test_language.py

@@ -0,0 +1,156 @@
+#!/usr/bin/env python
+
+import pytest
+
+pytest.importorskip("datasets", reason="datasets is required (install lerobot[dataset])")
+pytest.importorskip("pandas", reason="pandas is required (install lerobot[dataset])")
+
+import numpy as np  # noqa: E402
+import pandas as pd  # noqa: E402
+import pyarrow as pa  # noqa: E402
+
+from lerobot.datasets import LeRobotDataset  # noqa: E402
+from lerobot.datasets.io_utils import write_info  # noqa: E402
+from lerobot.datasets.language import (  # noqa: E402
+    EVENT_ONLY_STYLES,
+    LANGUAGE_EVENTS,
+    LANGUAGE_PERSISTENT,
+    PERSISTENT_STYLES,
+    STYLE_REGISTRY,
+    VIEW_DEPENDENT_STYLES,
+    column_for_style,
+    is_view_dependent_style,
+    language_events_arrow_type,
+    language_feature_info,
+    language_persistent_arrow_type,
+    validate_camera_field,
+)
+from lerobot.datasets.utils import DEFAULT_DATA_PATH  # noqa: E402
+
+
+def test_language_arrow_schema_has_expected_fields():
+    persistent_row_type = language_persistent_arrow_type().value_type
+    event_row_type = language_events_arrow_type().value_type
+
+    assert isinstance(persistent_row_type, pa.StructType)
+    assert persistent_row_type.names == [
+        "role",
+        "content",
+        "style",
+        "timestamp",
+        "camera",
+        "tool_calls",
+    ]
+
+    assert isinstance(event_row_type, pa.StructType)
+    assert event_row_type.names == ["role", "content", "style", "camera", "tool_calls"]
+
+
+def test_style_registry_routes_columns():
+    assert {"subtask", "plan", "memory", "motion", "task_aug"} == PERSISTENT_STYLES
+    assert {"interjection", "vqa", "trace"} == EVENT_ONLY_STYLES
+    assert PERSISTENT_STYLES | EVENT_ONLY_STYLES <= STYLE_REGISTRY
+
+    assert column_for_style("subtask") == LANGUAGE_PERSISTENT
+    assert column_for_style("plan") == LANGUAGE_PERSISTENT
+    assert column_for_style("memory") == LANGUAGE_PERSISTENT
+    assert column_for_style("motion") == LANGUAGE_PERSISTENT
+    assert column_for_style("task_aug") == LANGUAGE_PERSISTENT
+    assert column_for_style("interjection") == LANGUAGE_EVENTS
+    assert column_for_style("vqa") == LANGUAGE_EVENTS
+    assert column_for_style("trace") == LANGUAGE_EVENTS
+    assert column_for_style(None) == LANGUAGE_EVENTS
+
+
+def test_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("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")
+    assert not is_view_dependent_style(None)
+
+
+def test_validate_camera_field_requires_camera_for_view_dependent_styles():
+    validate_camera_field("vqa", "observation.images.top")
+    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("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"):
+        validate_camera_field(None, "observation.images.top")
+
+
+def test_unknown_style_rejected():
+    with pytest.raises(ValueError, match="Unknown language style"):
+        column_for_style("surprise")
+
+
+def test_lerobot_dataset_passes_language_columns_through(tmp_path, empty_lerobot_dataset_factory):
+    root = tmp_path / "language_dataset"
+    dataset = empty_lerobot_dataset_factory(
+        root=root,
+        features={"state": {"dtype": "float32", "shape": (2,), "names": None}},
+        use_videos=False,
+    )
+    dataset.add_frame({"state": np.array([0.0, 1.0], dtype=np.float32), "task": "tidy"})
+    dataset.add_frame({"state": np.array([1.0, 2.0], dtype=np.float32), "task": "tidy"})
+    dataset.save_episode()
+    dataset.finalize()
+
+    persistent = [
+        {
+            "role": "assistant",
+            "content": "reach for the cup",
+            "style": "subtask",
+            "timestamp": 0.0,
+            "camera": None,
+            "tool_calls": None,
+        }
+    ]
+    event = {
+        "role": "user",
+        "content": "what is visible?",
+        "style": "vqa",
+        "camera": "observation.images.top",
+        "tool_calls": None,
+    }
+    data_path = root / DEFAULT_DATA_PATH.format(chunk_index=0, file_index=0)
+    df = pd.read_parquet(data_path)
+    df[LANGUAGE_PERSISTENT] = [persistent, persistent]
+    df[LANGUAGE_EVENTS] = [[event], []]
+    df.to_parquet(data_path)
+
+    info = dataset.meta.info
+    info["features"].update(language_feature_info())
+    write_info(info, root)
+
+    reloaded = LeRobotDataset(repo_id=dataset.repo_id, root=root)
+
+    first = reloaded[0]
+    second = reloaded[1]
+    assert first[LANGUAGE_PERSISTENT] == persistent
+    assert first[LANGUAGE_EVENTS] == [event]
+    assert second[LANGUAGE_PERSISTENT] == persistent
+    assert second[LANGUAGE_EVENTS] == []

tests/datasets/test_language_render.py

@@ -0,0 +1,417 @@
+#!/usr/bin/env python
+
+import pytest
+
+pytest.importorskip("datasets", reason="datasets is required (install lerobot[dataset])")
+
+from lerobot.configs.recipe import MessageTurn, TrainingRecipe  # noqa: E402
+from lerobot.datasets.language_render import (  # noqa: E402
+    EMITTED_AT_TOLERANCE_S,
+    active_at,
+    emitted_at,
+    nth_next,
+    nth_prev,
+    render_sample,
+)
+
+
+def persistent_row(role, content, style, timestamp, tool_calls=None, camera=None):
+    return {
+        "role": role,
+        "content": content,
+        "style": style,
+        "timestamp": timestamp,
+        "camera": camera,
+        "tool_calls": tool_calls,
+    }
+
+
+def event_row(role, content, style, tool_calls=None, camera=None):
+    return {
+        "role": role,
+        "content": content,
+        "style": style,
+        "camera": camera,
+        "tool_calls": tool_calls,
+    }
+
+
+PERSISTENT = [
+    persistent_row("assistant", "plan 0", "plan", 0.0),
+    persistent_row("assistant", "memory 0", "memory", 0.0),
+    persistent_row("assistant", "subtask 0", "subtask", 0.0),
+    persistent_row("assistant", "memory 1", "memory", 1.0),
+    persistent_row("assistant", "subtask 1", "subtask", 1.0),
+]
+EVENTS_AT_1 = [
+    event_row("user", "what is visible?", "vqa", camera="observation.images.top"),
+    event_row("assistant", '{"count": 2}', "vqa", camera="observation.images.top"),
+]
+EVENTS_AT_2 = [
+    event_row("user", "skip wiping", "interjection"),
+    event_row(
+        "assistant",
+        None,
+        None,
+        [{"type": "function", "function": {"name": "say", "arguments": {"text": "Skipping wiping."}}}],
+    ),
+]
+# Same emission tick, two cameras: triggers per-camera disambiguation in
+# resolvers, mirroring how Module 3 of the annotation pipeline writes one
+# (vqa, user) + (vqa, assistant) pair per camera.
+EVENTS_AT_3_TWO_CAMERAS = [
+    event_row("user", "how many cups (top)?", "vqa", camera="observation.images.top"),
+    event_row("assistant", '{"count": 3}', "vqa", camera="observation.images.top"),
+    event_row("user", "how many cups (wrist)?", "vqa", camera="observation.images.wrist"),
+    event_row("assistant", '{"count": 1}', "vqa", camera="observation.images.wrist"),
+]
+
+
+def test_resolver_temporal_semantics():
+    assert active_at(0.5, persistent=PERSISTENT, style="subtask")["content"] == "subtask 0"
+    assert active_at(1.0, persistent=PERSISTENT, style="subtask")["content"] == "subtask 1"
+    assert emitted_at(0.5, persistent=PERSISTENT, events=[], style="vqa", role="assistant") is None
+    assert (
+        emitted_at(1.0, persistent=PERSISTENT, events=EVENTS_AT_1, style="vqa", role="assistant")["content"]
+        == '{"count": 2}'
+    )
+
+
+def test_persistent_relative_resolvers_reject_event_styles():
+    with pytest.raises(ValueError, match="event-only"):
+        active_at(1.0, persistent=PERSISTENT, style="vqa")
+    with pytest.raises(ValueError, match="event-only"):
+        nth_prev(1.0, persistent=PERSISTENT, style="interjection")
+
+
+def test_nth_prev_and_next():
+    assert nth_prev(1.0, persistent=PERSISTENT, style="subtask", offset=1)["content"] == "subtask 0"
+    assert nth_next(0.0, persistent=PERSISTENT, style="subtask", offset=1)["content"] == "subtask 1"
+
+
+def test_substitution_if_present_multimodal_and_tool_calls():
+    recipe = TrainingRecipe(
+        messages=[
+            MessageTurn(
+                role="user",
+                content=[
+                    {"type": "image", "feature": "observation.images.top"},
+                    {"type": "text", "text": "${task}: ${interjection}"},
+                ],
+                stream="high_level",
+                if_present="interjection",
+            ),
+            MessageTurn(
+                role="assistant",
+                content="${plan}",
+                stream="high_level",
+                target=True,
+                tool_calls_from="speech",
+            ),
+        ],
+        bindings={"plan": "active_at(t, style=plan)"},
+    )
+
+    rendered = render_sample(
+        recipe=recipe,
+        persistent=PERSISTENT,
+        events=EVENTS_AT_2,
+        t=2.0,
+        sample_idx=0,
+        task="clean kitchen",
+    )
+
+    assert rendered["messages"][0]["content"][1]["text"] == "clean kitchen: skip wiping"
+    assert rendered["messages"][1]["content"] == "plan 0"
+    assert rendered["messages"][1]["tool_calls"][0]["function"]["name"] == "say"
+    assert rendered["message_streams"] == ["high_level", "high_level"]
+    assert rendered["target_message_indices"] == [1]
+
+
+def test_exact_event_miss_returns_none_when_target_skips():
+    recipe = TrainingRecipe(
+        messages=[
+            MessageTurn(role="user", content="${vqa_query}", stream="high_level", if_present="vqa_query"),
+            MessageTurn(
+                role="assistant",
+                content="${vqa}",
+                stream="high_level",
+                target=True,
+                if_present="vqa",
+            ),
+        ]
+    )
+
+    assert (
+        render_sample(recipe=recipe, persistent=PERSISTENT, events=EVENTS_AT_2, t=0.0, sample_idx=0) is None
+    )
+
+
+def test_deterministic_blend_sampling():
+    recipe = TrainingRecipe(
+        blend={
+            "a": TrainingRecipe(
+                weight=1.0,
+                messages=[
+                    MessageTurn(role="user", content="${task}", stream="high_level"),
+                    MessageTurn(role="assistant", content="a", stream="high_level", target=True),
+                ],
+            ),
+            "b": TrainingRecipe(
+                weight=1.0,
+                messages=[
+                    MessageTurn(role="user", content="${task}", stream="high_level"),
+                    MessageTurn(role="assistant", content="b", stream="high_level", target=True),
+                ],
+            ),
+        }
+    )
+
+    first = render_sample(
+        recipe=recipe, persistent=PERSISTENT, events=EVENTS_AT_2, t=0.0, sample_idx=123, task="x"
+    )
+    second = render_sample(
+        recipe=recipe, persistent=PERSISTENT, events=EVENTS_AT_2, t=0.0, sample_idx=123, task="x"
+    )
+    assert first == second
+
+
+def test_emitted_at_filters_vqa_by_camera():
+    top = emitted_at(
+        3.0,
+        persistent=PERSISTENT,
+        events=EVENTS_AT_3_TWO_CAMERAS,
+        style="vqa",
+        role="assistant",
+        camera="observation.images.top",
+    )
+    wrist = emitted_at(
+        3.0,
+        persistent=PERSISTENT,
+        events=EVENTS_AT_3_TWO_CAMERAS,
+        style="vqa",
+        role="assistant",
+        camera="observation.images.wrist",
+    )
+    assert top["content"] == '{"count": 3}'
+    assert wrist["content"] == '{"count": 1}'
+
+
+def test_emitted_at_raises_on_ambiguous_per_camera_vqa():
+    with pytest.raises(ValueError, match="Ambiguous resolver"):
+        emitted_at(
+            3.0,
+            persistent=PERSISTENT,
+            events=EVENTS_AT_3_TWO_CAMERAS,
+            style="vqa",
+            role="assistant",
+        )
+
+
+def _vqa_subrecipe(camera: str) -> TrainingRecipe:
+    return TrainingRecipe(
+        weight=1.0,
+        bindings={
+            "vqa_query": f"emitted_at(t, style=vqa, role=user, camera={camera})",
+            "vqa": f"emitted_at(t, style=vqa, role=assistant, camera={camera})",
+        },
+        messages=[
+            MessageTurn(
+                role="user",
+                content=[{"type": "image", "feature": camera}, {"type": "text", "text": "${vqa_query}"}],
+                stream="high_level",
+                if_present="vqa_query",
+            ),
+            MessageTurn(
+                role="assistant",
+                content="${vqa}",
+                stream="high_level",
+                target=True,
+                if_present="vqa",
+            ),
+        ],
+    )
+
+
+@pytest.mark.parametrize(
+    ("camera", "expected_query", "expected_answer"),
+    [
+        ("observation.images.top", "how many cups (top)?", '{"count": 3}'),
+        ("observation.images.wrist", "how many cups (wrist)?", '{"count": 1}'),
+    ],
+)
+def test_per_camera_blend_renders_both_views(camera, expected_query, expected_answer):
+    rendered = render_sample(
+        recipe=_vqa_subrecipe(camera),
+        persistent=PERSISTENT,
+        events=EVENTS_AT_3_TWO_CAMERAS,
+        t=3.0,
+        sample_idx=0,
+    )
+
+    assert rendered["messages"][0]["content"][0]["feature"] == camera
+    assert rendered["messages"][0]["content"][1]["text"] == expected_query
+    assert rendered["messages"][1]["content"] == expected_answer
+
+
+def test_resolve_task_picks_rephrasing_deterministically_per_sample():
+    rephrasings = [
+        persistent_row("user", "tidy the kitchen", "task_aug", 0.0),
+        persistent_row("user", "please clean up the kitchen", "task_aug", 0.0),
+        persistent_row("user", "kitchen needs tidying", "task_aug", 0.0),
+        persistent_row("user", "make the kitchen clean", "task_aug", 0.0),
+    ]
+    recipe = TrainingRecipe(
+        messages=[
+            MessageTurn(role="user", content="${task}", stream="high_level"),
+            MessageTurn(role="assistant", content="ok", stream="high_level", target=True),
+        ]
+    )
+
+    # No explicit task override → resolver consults persistent rows.
+    seen: set[str] = set()
+    for sample_idx in range(64):
+        rendered = render_sample(
+            recipe=recipe,
+            persistent=rephrasings,
+            events=[],
+            t=0.0,
+            sample_idx=sample_idx,
+            dataset_ctx={"task": "canonical kitchen task"},
+        )
+        seen.add(rendered["messages"][0]["content"])
+    # Every rephrasing should be reachable across enough samples.
+    assert seen == {r["content"] for r in rephrasings}
+    # Same sample_idx → same pick (determinism).
+    a = render_sample(
+        recipe=recipe,
+        persistent=rephrasings,
+        events=[],
+        t=0.0,
+        sample_idx=42,
+        dataset_ctx={"task": "canonical"},
+    )
+    b = render_sample(
+        recipe=recipe,
+        persistent=rephrasings,
+        events=[],
+        t=0.0,
+        sample_idx=42,
+        dataset_ctx={"task": "canonical"},
+    )
+    assert a["messages"][0]["content"] == b["messages"][0]["content"]
+
+
+def test_resolve_task_falls_back_to_canonical_without_rephrasings():
+    recipe = TrainingRecipe(
+        messages=[
+            MessageTurn(role="user", content="${task}", stream="high_level"),
+            MessageTurn(role="assistant", content="ok", stream="high_level", target=True),
+        ]
+    )
+    rendered = render_sample(
+        recipe=recipe,
+        persistent=PERSISTENT,  # no task_aug rows
+        events=[],
+        t=0.0,
+        sample_idx=0,
+        dataset_ctx={"task": "clean the kitchen"},
+    )
+    assert rendered["messages"][0]["content"] == "clean the kitchen"
+
+
+def test_resolve_task_explicit_override_beats_rephrasings():
+    rephrasings = [
+        persistent_row("user", "rephrased one", "task_aug", 0.0),
+        persistent_row("user", "rephrased two", "task_aug", 0.0),
+    ]
+    recipe = TrainingRecipe(
+        messages=[
+            MessageTurn(role="user", content="${task}", stream="high_level"),
+            MessageTurn(role="assistant", content="ok", stream="high_level", target=True),
+        ]
+    )
+    rendered = render_sample(
+        recipe=recipe,
+        persistent=rephrasings,
+        events=[],
+        t=0.0,
+        sample_idx=0,
+        task="explicit override wins",
+        dataset_ctx={"task": "canonical"},
+    )
+    assert rendered["messages"][0]["content"] == "explicit override wins"
+
+
+def test_emitted_at_persistent_tolerates_small_timestamp_drift():
+    """Persistent ``emitted_at`` should match within EMITTED_AT_TOLERANCE_S
+    so callers that derive ``t`` arithmetically (``frame_idx / fps``) still
+    line up with the parquet-stored timestamp.
+    """
+    rows = [persistent_row("assistant", "memo", "memory", 1.0)]
+    # Half a tolerance window — bit-different float, comfortably inside
+    inside = emitted_at(1.0 + EMITTED_AT_TOLERANCE_S / 2, persistent=rows, events=[], style="memory")
+    assert inside is not None and inside["content"] == "memo"
+
+    # Just past the window — no match
+    outside = emitted_at(1.0 + EMITTED_AT_TOLERANCE_S * 2, persistent=rows, events=[], style="memory")
+    assert outside is None
+
+
+def test_render_sample_rejects_non_dict_language_rows():
+    """``_normalize_rows`` must surface malformed inputs as TypeError.
+
+    A pipeline that hands the renderer a non-dict (e.g. a stray string)
+    is a real upstream bug — silent skipping would let it propagate.
+    """
+    recipe = TrainingRecipe(
+        messages=[
+            MessageTurn(role="user", content="${task}", stream="high_level"),
+            MessageTurn(role="assistant", content="ok", stream="high_level", target=True),
+        ]
+    )
+    with pytest.raises(TypeError, match="must be dictionaries"):
+        render_sample(
+            recipe=recipe,
+            persistent=["not a dict"],
+            events=[],
+            t=0.0,
+            sample_idx=0,
+            task="x",
+        )
+
+
+def test_low_level_branch_renders_active_subtask():
+    low_level = TrainingRecipe(
+        blend={
+            "low": TrainingRecipe(
+                weight=1.0,
+                messages=[
+                    MessageTurn(
+                        role="user",
+                        content="${task}\nPlan: ${plan}\nMemory: ${memory}",
+                        stream="high_level",
+                    ),
+                    MessageTurn(
+                        role="assistant",
+                        content="${subtask}",
+                        stream="low_level",
+                        target=True,
+                    ),
+                ],
+            )
+        }
+    )
+
+    rendered = render_sample(
+        recipe=low_level,
+        persistent=PERSISTENT,
+        events=[],
+        t=0.5,
+        sample_idx=0,
+        task="clean kitchen",
+    )
+
+    assert rendered["messages"][-1] == {"role": "assistant", "content": "subtask 0"}
+    assert rendered["message_streams"][-1] == "low_level"
+    assert rendered["target_message_indices"] == [1]

tests/datasets/test_subtask_dataset.py

@@ -1,193 +0,0 @@
-#!/usr/bin/env python
-
-# Copyright 2026 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.
-
-"""
-Tests for subtask functionality in LeRobotDataset.
-
-These tests verify that:
-- Subtask information is correctly loaded from datasets that have subtask data
-- The __getitem__ method correctly adds subtask strings to returned items
-- Subtask handling gracefully handles missing data
-"""
-
-import pytest
-
-pytest.importorskip("pandas", reason="pandas is required (install lerobot[dataset])")
-
-import pandas as pd  # noqa: E402
-import torch
-
-from lerobot.datasets.lerobot_dataset import LeRobotDataset
-
-
-class TestSubtaskDataset:
-    """Tests for subtask handling in LeRobotDataset."""
-
-    @pytest.fixture
-    def subtask_dataset(self):
-        """Load the test subtask dataset from the hub."""
-        # Use lerobot/pusht-subtask dataset with episode 1
-        return LeRobotDataset(
-            repo_id="lerobot/pusht-subtask",
-            episodes=[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11],
-        )
-
-    def test_subtask_dataset_loads(self, subtask_dataset):
-        """Test that the subtask dataset loads successfully."""
-        assert subtask_dataset is not None
-        assert len(subtask_dataset) > 0
-
-    def test_subtask_metadata_loaded(self, subtask_dataset):
-        """Test that subtask metadata is loaded when present in dataset."""
-        # The dataset should have subtasks metadata loaded
-        assert subtask_dataset.meta.subtasks is not None
-        assert isinstance(subtask_dataset.meta.subtasks, pd.DataFrame)
-
-    def test_subtask_index_in_features(self, subtask_dataset):
-        """Test that subtask_index is a feature when dataset has subtasks."""
-        assert "subtask_index" in subtask_dataset.features
-
-    def test_getitem_returns_subtask_string(self, subtask_dataset):
-        """Test that __getitem__ correctly adds subtask string to returned item."""
-        item = subtask_dataset[0]
-
-        # Subtask should be present in the returned item
-        assert "subtask" in item
-        assert isinstance(item["subtask"], str)
-        assert len(item["subtask"]) > 0  # Should not be empty
-
-    def test_getitem_has_subtask_index(self, subtask_dataset):
-        """Test that __getitem__ includes subtask_index."""
-        item = subtask_dataset[0]
-
-        assert "subtask_index" in item
-        assert isinstance(item["subtask_index"], torch.Tensor)
-
-    def test_subtask_index_maps_to_valid_subtask(self, subtask_dataset):
-        """Test that subtask_index correctly maps to a subtask in metadata."""
-        item = subtask_dataset[0]
-
-        subtask_idx = item["subtask_index"].item()
-        subtask_from_metadata = subtask_dataset.meta.subtasks.iloc[subtask_idx].name
-
-        assert item["subtask"] == subtask_from_metadata
-
-    def test_all_items_have_subtask(self, subtask_dataset):
-        """Test that all items in the dataset have subtask information."""
-        for i in range(min(len(subtask_dataset), 5)):  # Check first 5 items
-            item = subtask_dataset[i]
-            assert "subtask" in item
-            assert isinstance(item["subtask"], str)
-
-    def test_task_and_subtask_coexist(self, subtask_dataset):
-        """Test that both task and subtask are present in returned items."""
-        item = subtask_dataset[0]
-
-        # Both task and subtask should be present
-        assert "task" in item
-        assert "subtask" in item
-        assert isinstance(item["task"], str)
-        assert isinstance(item["subtask"], str)
-
-
-class TestSubtaskDatasetMissing:
-    """Tests for graceful handling when subtask data is missing."""
-
-    @pytest.fixture
-    def dataset_without_subtasks(self, tmp_path, empty_lerobot_dataset_factory):
-        """Create a dataset without subtask information."""
-        features = {"state": {"dtype": "float32", "shape": (2,), "names": None}}
-        dataset = empty_lerobot_dataset_factory(root=tmp_path / "no_subtask", features=features)
-
-        # Add some frames and save
-        for _ in range(5):
-            dataset.add_frame({"state": torch.randn(2), "task": "Test task"})
-        dataset.save_episode()
-        dataset.finalize()
-
-        # Reload the dataset
-        return LeRobotDataset(dataset.repo_id, root=dataset.root)
-
-    def test_no_subtask_in_features(self, dataset_without_subtasks):
-        """Test that subtask_index is not in features when not provided."""
-        assert "subtask_index" not in dataset_without_subtasks.features
-
-    def test_getitem_without_subtask(self, dataset_without_subtasks):
-        """Test that __getitem__ works when subtask is not present."""
-        item = dataset_without_subtasks[0]
-
-        # Item should still be retrievable
-        assert item is not None
-        assert "state" in item
-        assert "task" in item
-
-        # Subtask should NOT be present
-        assert "subtask" not in item
-
-    def test_subtasks_metadata_is_none(self, dataset_without_subtasks):
-        """Test that subtasks metadata is None when not present."""
-        assert dataset_without_subtasks.meta.subtasks is None
-
-
-class TestSubtaskEdgeCases:
-    """Edge case tests for subtask handling."""
-
-    def test_subtask_with_multiple_episodes(self):
-        """Test subtask handling with multiple episodes if available."""
-        try:
-            dataset = LeRobotDataset(
-                repo_id="lerobot/pusht-subtask",
-                episodes=[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11],
-            )
-        except Exception:
-            pytest.skip("Could not load test-subtask dataset")
-
-        # Check first and last items have valid subtasks
-        first_item = dataset[0]
-        last_item = dataset[len(dataset) - 1]
-
-        assert "subtask" in first_item
-        assert "subtask" in last_item
-        assert isinstance(first_item["subtask"], str)
-        assert isinstance(last_item["subtask"], str)
-
-    def test_subtask_index_consistency(self):
-        """Test that same subtask_index returns same subtask string."""
-        try:
-            dataset = LeRobotDataset(
-                repo_id="lerobot/pusht-subtask",
-                episodes=[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11],
-            )
-        except Exception:
-            pytest.skip("Could not load test-subtask dataset")
-
-        if len(dataset) < 2:
-            pytest.skip("Dataset too small for this test")
-
-        # Collect subtask_index to subtask mappings
-        subtask_map = {}
-        for i in range(min(len(dataset), 10)):
-            item = dataset[i]
-            idx = item["subtask_index"].item()
-            subtask = item["subtask"]
-
-            if idx in subtask_map:
-                # Same index should always return same subtask
-                assert subtask_map[idx] == subtask, (
-                    f"Inconsistent subtask for index {idx}: '{subtask_map[idx]}' vs '{subtask}'"
-                )
-            else:
-                subtask_map[idx] = subtask

tests/processor/test_render_messages_processor.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python
+
+import pytest
+
+pytest.importorskip("datasets", reason="datasets is required (install lerobot[dataset])")
+
+import torch  # noqa: E402
+
+from lerobot.configs.recipe import MessageTurn, TrainingRecipe  # noqa: E402
+from lerobot.processor.converters import create_transition  # noqa: E402
+from lerobot.processor.render_messages_processor import RenderMessagesStep  # noqa: E402
+from lerobot.types import TransitionKey  # noqa: E402
+
+
+def test_render_messages_step_noops_without_language_columns():
+    recipe = TrainingRecipe(
+        messages=[
+            MessageTurn(role="user", content="${task}", stream="high_level"),
+            MessageTurn(role="assistant", content="${subtask}", stream="low_level", target=True),
+        ]
+    )
+    transition = create_transition(complementary_data={"task": "do it"})
+
+    assert RenderMessagesStep(recipe)(transition) == transition
+
+
+def test_render_messages_step_renders_and_drops_raw_language():
+    recipe = TrainingRecipe(
+        messages=[
+            MessageTurn(role="user", content="${task}", stream="high_level"),
+            MessageTurn(role="assistant", content="${subtask}", stream="low_level", target=True),
+        ]
+    )
+    transition = create_transition(
+        complementary_data={
+            "task": "do it",
+            "timestamp": torch.tensor(0.0),
+            "index": torch.tensor(7),
+            "language_persistent": [
+                {
+                    "role": "assistant",
+                    "content": "reach carefully",
+                    "style": "subtask",
+                    "timestamp": 0.0,
+                    "camera": None,
+                    "tool_calls": None,
+                }
+            ],
+            "language_events": [],
+        }
+    )
+
+    out = RenderMessagesStep(recipe)(transition)
+    data = out[TransitionKey.COMPLEMENTARY_DATA]
+
+    assert "language_persistent" not in data
+    assert "language_events" not in data
+    assert data["messages"][-1]["content"] == "reach carefully"
+    assert data["message_streams"] == ["high_level", "low_level"]
+    assert data["target_message_indices"] == [1]

tests/utils/test_collate.py

@@ -0,0 +1,84 @@
+#!/usr/bin/env python
+
+import pytest
+
+pytest.importorskip("datasets", reason="datasets is required (install lerobot[dataset])")
+
+import torch  # noqa: E402
+
+from lerobot.utils.collate import lerobot_collate_fn  # noqa: E402
+
+
+def test_lerobot_collate_preserves_messages_and_drops_raw_language():
+    batch = [
+        {
+            "index": torch.tensor(0),
+            "messages": [{"role": "assistant", "content": "a"}],
+            "message_streams": ["low_level"],
+            "target_message_indices": [0],
+            "language_persistent": [{"content": "raw"}],
+            "language_events": [],
+        },
+        {
+            "index": torch.tensor(1),
+            "messages": [{"role": "assistant", "content": "b"}],
+            "message_streams": ["low_level"],
+            "target_message_indices": [0],
+            "language_persistent": [{"content": "raw"}],
+            "language_events": [],
+        },
+    ]
+
+    out = lerobot_collate_fn(batch)
+
+    assert out["index"].tolist() == [0, 1]
+    assert out["messages"][0][0]["content"] == "a"
+    assert out["messages"][1][0]["content"] == "b"
+    assert out["message_streams"] == [["low_level"], ["low_level"]]
+    assert out["target_message_indices"] == [[0], [0]]
+    assert "language_persistent" not in out
+    assert "language_events" not in out
+
+
+def test_lerobot_collate_passes_through_standard_batch():
+    """On a non-language batch, the collate must match ``default_collate``.
+
+    Guards against silent regressions: ``lerobot_train.py`` only opts into
+    ``lerobot_collate_fn`` when the dataset declares language columns, but
+    if a future change ever wires it in unconditionally we want the
+    behavior to remain a transparent pass-through for ordinary tensor
+    batches.
+    """
+    from torch.utils.data._utils.collate import default_collate
+
+    batch = [
+        {
+            "observation.image": torch.zeros(3, 4, 4),
+            "action": torch.tensor([0.0, 1.0]),
+            "index": torch.tensor(0),
+        },
+        {
+            "observation.image": torch.ones(3, 4, 4),
+            "action": torch.tensor([2.0, 3.0]),
+            "index": torch.tensor(1),
+        },
+    ]
+
+    custom = lerobot_collate_fn(batch)
+    expected = default_collate(batch)
+
+    assert custom.keys() == expected.keys()
+    for key in expected:
+        assert torch.equal(custom[key], expected[key]), f"key={key} diverged"
+
+
+def test_lerobot_collate_drops_none_samples():
+    """Recipes that yielded no target message return ``None`` — those samples
+    must be filtered out, and an entirely-``None`` batch must collapse to ``None``.
+    """
+    batch = [None, {"index": torch.tensor(0)}, None]
+    out = lerobot_collate_fn(batch)
+    assert out is not None
+    assert out["index"].tolist() == [0]
+
+    assert lerobot_collate_fn([None, None]) is None