adding relative joint exclude test

* refactor(processors): share policy pipeline builders

* Apply suggestions from code review

Co-authored-by: Martino Russi <77496684+nepyope@users.noreply.github.com>
Signed-off-by: Steven Palma <imstevenpmwork@ieee.org>

* fix(processor): solve style after commit suggestions

---------

Signed-off-by: Steven Palma <imstevenpmwork@ieee.org>
Co-authored-by: Martino Russi <77496684+nepyope@users.noreply.github.com>

docs/source/bring_your_own_policies.mdx

@@ -150,14 +150,14 @@ class MyPolicy(PreTrainedPolicy):
 
 The methods called by the train/eval loops:
 
-| 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).                                                                                                                                           |
+| 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 (see `get_optim_params` in [`modeling_act.py`](https://github.com/huggingface/lerobot/blob/main/src/lerobot/policies/act/modeling_act.py) for a per-group learning-rate example). |
+| `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.
 
@@ -295,12 +295,10 @@ The file names are load-bearing: the factory does lazy imports by name, and the
 
 ### Wiring
 
-Four places need to know about your policy. All by name.
+Two 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.
-4. **`templates/lerobot_modelcard_template.md` and the root `README.md`** — the template is what `push_model_to_hub` renders into the model card of every checkpoint trained with your policy: add a one-line description of your policy in the `model_name` branches, map it in `policy_docs` so cards link to your MDX guide, and optionally add an architecture image to `diagrams`. Then add your policy to the models table in the root `README.md`, under the right category, linking to your doc page.
+1. **`policies/__init__.py`** — re-export `MyPolicyConfig` and add it to `__all__`. This import is what registers your policy: `@PreTrainedConfig.register_subclass("my_policy")` runs, and from then on the factory resolves everything by convention. **Don't** re-export the modeling class; it loads lazily through the factory (so `import lerobot` stays fast).
+2. **`templates/lerobot_modelcard_template.md` and the root `README.md`** — the template is what `push_model_to_hub` renders into the model card of every checkpoint trained with your policy: add a one-line description of your policy in the `model_name` branches, map it in `policy_docs` so cards link to your MDX guide, and optionally add an architecture image to `diagrams`. Then add your policy to the models table in the root `README.md`, under the right category, linking to your doc page.
 
 Mirror an existing policy that's structurally similar to yours; the diff is small.
 
@@ -332,6 +330,10 @@ This way:
 
 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.
 
+### Avoid copying a modeling file — subclass it
+
+If your policy needs to modify a backbone that already exists in `transformers` (custom conditioning, extra inputs, a swapped sub-module), **do not vendor a copy of its `modeling_*.py`**. Instead, subclass the smallest upstream unit and override only what changes. [`pi_gemma.py`](https://github.com/huggingface/lerobot/blob/main/src/lerobot/policies/pi_gemma.py) is the canonical reference: it injects AdaRMS conditioning into PaliGemma/Gemma in ~370 lines by subclassing `GemmaModel`/`PaliGemmaModel` and overriding the decoder-layer forward, instead of forking the ~2,000-line modeling file. Model surgery on a _loaded_ native model is also fine (layer truncation, tokenizer expansion, hidden-state capture — see `evo1/internvl3_embedder.py`, `eo1/modeling_eo1.py`, `groot/groot_n1_7.py` for working examples). Reviewers will ask for this pattern when a PR arrives with a copied modeling file; the only accepted exception is a model that does not exist in `transformers` at all.
+
 ### 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.
@@ -367,7 +369,7 @@ If your policy is real-robot-only and no sim benchmark applies, swap the sim eva
 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).
+- [ ] `policies/__init__.py` re-exports the config (this registers the policy; the factory resolves modeling/processor by naming convention).
 - [ ] `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/configs/policies.py

@@ -205,24 +205,30 @@ class PreTrainedConfig(draccus.ChoiceRegistry, HubMixin, abc.ABC):  # type: igno
                     f"{CONFIG_NAME} not found on the HuggingFace Hub in {model_id}"
                 ) from e
 
-        # HACK: Parse the original config to get the config subclass, so that we can
-        # apply cli overrides.
-        # This is very ugly, ideally we'd like to be able to do that natively with draccus
-        # something like --policy.path (in addition to --policy.type)
-        with draccus.config_type("json"):
-            orig_config = draccus.parse(cls, config_file, args=[])
-
         if config_file is None:
             raise FileNotFoundError(f"{CONFIG_NAME} not found in {model_id}")
 
         with open(config_file) as f:
             config = json.load(f)
 
-        config.pop("type")
+        # Resolve the concrete config subclass from the serialized "type" tag, then parse
+        # the config (with CLI overrides) directly for that class. The "type" key is
+        # stripped because draccus only consumes it when parsing the registry base class.
+        policy_type = config.pop("type", None)
+        if policy_type is None:
+            raise ValueError(f"Missing 'type' field in {CONFIG_NAME} of {model_id}")
+        try:
+            config_cls = cls.get_choice_class(policy_type)
+        except Exception as e:
+            raise ValueError(
+                f"Policy type '{policy_type}' (from {CONFIG_NAME} of {model_id}) is not registered. "
+                f"Available policy types: {cls.get_known_choices()}"
+            ) from e
+
         with tempfile.NamedTemporaryFile("w+", delete=False, suffix=".json") as f:
             json.dump(config, f)
             config_file = f.name
 
         cli_overrides = policy_kwargs.pop("cli_overrides", [])
         with draccus.config_type("json"):
-            return draccus.parse(orig_config.__class__, config_file, args=cli_overrides)
+            return draccus.parse(config_cls, config_file, args=cli_overrides)

src/lerobot/policies/__init__.py

@@ -32,6 +32,7 @@ from .pretrained import PreTrainedPolicy as PreTrainedPolicy
 from .smolvla.configuration_smolvla import SmolVLAConfig as SmolVLAConfig
 from .tdmpc.configuration_tdmpc import TDMPCConfig as TDMPCConfig
 from .utils import make_robot_action, prepare_observation_for_inference
+from .vla_jepa.configuration_vla_jepa import VLAJEPAConfig as VLAJEPAConfig
 from .vqbet.configuration_vqbet import VQBeTConfig as VQBeTConfig
 from .wall_x.configuration_wall_x import WallXConfig as WallXConfig
 from .xvla.configuration_xvla import XVLAConfig as XVLAConfig
@@ -57,6 +58,7 @@ __all__ = [
     "PI05Config",
     "SmolVLAConfig",
     "TDMPCConfig",
+    "VLAJEPAConfig",
     "VQBeTConfig",
     "WallXConfig",
     "XVLAConfig",

src/lerobot/policies/act/processor_act.py

@@ -18,17 +18,10 @@ from typing import Any
 import torch
 
 from lerobot.processor import (
-    AddBatchDimensionProcessorStep,
-    DeviceProcessorStep,
-    NormalizerProcessorStep,
     PolicyAction,
     PolicyProcessorPipeline,
-    RenameObservationsProcessorStep,
-    UnnormalizerProcessorStep,
-    policy_action_to_transition,
-    transition_to_policy_action,
+    make_default_pre_post_processors,
 )
-from lerobot.utils.constants import POLICY_POSTPROCESSOR_DEFAULT_NAME, POLICY_PREPROCESSOR_DEFAULT_NAME
 
 from .configuration_act import ACTConfig
 
@@ -54,34 +47,4 @@ def make_act_pre_post_processors(
         tuple[PolicyProcessorPipeline[dict[str, Any], dict[str, Any]], PolicyProcessorPipeline[PolicyAction, PolicyAction]]: A tuple containing the
         pre-processor pipeline and the post-processor pipeline.
     """
-
-    input_steps = [
-        RenameObservationsProcessorStep(rename_map={}),
-        AddBatchDimensionProcessorStep(),
-        DeviceProcessorStep(device=config.device),
-        NormalizerProcessorStep(
-            features={**config.input_features, **config.output_features},
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-            device=config.device,
-        ),
-    ]
-    output_steps = [
-        UnnormalizerProcessorStep(
-            features=config.output_features, norm_map=config.normalization_mapping, stats=dataset_stats
-        ),
-        DeviceProcessorStep(device="cpu"),
-    ]
-
-    return (
-        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
-            steps=input_steps,
-            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
-        ),
-        PolicyProcessorPipeline[PolicyAction, PolicyAction](
-            steps=output_steps,
-            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
-            to_transition=policy_action_to_transition,
-            to_output=transition_to_policy_action,
-        ),
-    )
+    return make_default_pre_post_processors(config, dataset_stats, normalizer_device=config.device)

src/lerobot/policies/diffusion/processor_diffusion.py

@@ -19,17 +19,10 @@ from typing import Any
 import torch
 
 from lerobot.processor import (
-    AddBatchDimensionProcessorStep,
-    DeviceProcessorStep,
-    NormalizerProcessorStep,
     PolicyAction,
     PolicyProcessorPipeline,
-    RenameObservationsProcessorStep,
-    UnnormalizerProcessorStep,
-    policy_action_to_transition,
-    transition_to_policy_action,
+    make_default_pre_post_processors,
 )
-from lerobot.utils.constants import POLICY_POSTPROCESSOR_DEFAULT_NAME, POLICY_PREPROCESSOR_DEFAULT_NAME
 
 from .configuration_diffusion import DiffusionConfig
 
@@ -63,32 +56,4 @@ def make_diffusion_pre_post_processors(
     Returns:
         A tuple containing the configured pre-processor and post-processor pipelines.
     """
-
-    input_steps = [
-        RenameObservationsProcessorStep(rename_map={}),
-        AddBatchDimensionProcessorStep(),
-        DeviceProcessorStep(device=config.device),
-        NormalizerProcessorStep(
-            features={**config.input_features, **config.output_features},
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-        ),
-    ]
-    output_steps = [
-        UnnormalizerProcessorStep(
-            features=config.output_features, norm_map=config.normalization_mapping, stats=dataset_stats
-        ),
-        DeviceProcessorStep(device="cpu"),
-    ]
-    return (
-        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
-            steps=input_steps,
-            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
-        ),
-        PolicyProcessorPipeline[PolicyAction, PolicyAction](
-            steps=output_steps,
-            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
-            to_transition=policy_action_to_transition,
-            to_output=transition_to_policy_action,
-        ),
-    )
+    return make_default_pre_post_processors(config, dataset_stats)

src/lerobot/policies/eo1/processor_eo1.py

@@ -23,24 +23,16 @@ import torch
 
 from lerobot.configs.types import FeatureType, PipelineFeatureType, PolicyFeature
 from lerobot.processor import (
-    AddBatchDimensionProcessorStep,
     ComplementaryDataProcessorStep,
-    DeviceProcessorStep,
-    NormalizerProcessorStep,
     PolicyAction,
     PolicyProcessorPipeline,
     ProcessorStep,
     ProcessorStepRegistry,
-    RenameObservationsProcessorStep,
-    UnnormalizerProcessorStep,
+    make_default_policy_processor_steps,
+    make_policy_processor_pipelines,
 )
-from lerobot.processor.converters import policy_action_to_transition, transition_to_policy_action
 from lerobot.types import TransitionKey
-from lerobot.utils.constants import (
-    OBS_STATE,
-    POLICY_POSTPROCESSOR_DEFAULT_NAME,
-    POLICY_PREPROCESSOR_DEFAULT_NAME,
-)
+from lerobot.utils.constants import OBS_STATE
 from lerobot.utils.import_utils import _transformers_available, require_package
 
 from .configuration_eo1 import EO1Config
@@ -242,14 +234,12 @@ def make_eo1_pre_post_processors(
 ]:
     """Build pre/post processor pipelines for EO1."""
 
+    steps = make_default_policy_processor_steps(config, dataset_stats)
+
     input_steps: list[ProcessorStep] = [
-        RenameObservationsProcessorStep(rename_map={}),
-        AddBatchDimensionProcessorStep(),
-        NormalizerProcessorStep(
-            features={**config.input_features, **config.output_features},
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-        ),
+        steps.rename_observations,
+        steps.add_batch_dim,
+        steps.normalize,
         EO1ConversationTemplateStep(input_features=config.input_features, chunk_size=config.chunk_size),
         EO1QwenProcessorStep(
             processor_name=config.vlm_base,
@@ -257,27 +247,12 @@ def make_eo1_pre_post_processors(
             image_max_pixels=config.image_max_pixels,
             use_fast_processor=config.use_fast_processor,
         ),
-        DeviceProcessorStep(device=config.device),
+        steps.to_device,
     ]
 
     output_steps: list[ProcessorStep] = [
-        UnnormalizerProcessorStep(
-            features=config.output_features,
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-        ),
-        DeviceProcessorStep(device="cpu"),
+        steps.unnormalize,
+        steps.to_cpu,
     ]
 
-    return (
-        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
-            steps=input_steps,
-            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
-        ),
-        PolicyProcessorPipeline[PolicyAction, PolicyAction](
-            steps=output_steps,
-            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
-            to_transition=policy_action_to_transition,
-            to_output=transition_to_policy_action,
-        ),
-    )
+    return make_policy_processor_pipelines(input_steps=input_steps, output_steps=output_steps)

src/lerobot/policies/factory.py

@@ -17,6 +17,7 @@
 from __future__ import annotations
 
 import importlib
+import inspect
 import logging
 from typing import TYPE_CHECKING, Any, TypedDict, Unpack
 
@@ -44,26 +45,10 @@ from lerobot.utils.constants import (
 )
 from lerobot.utils.feature_utils import dataset_to_policy_features
 
-from .act.configuration_act import ACTConfig
-from .diffusion.configuration_diffusion import DiffusionConfig
-from .eo1.configuration_eo1 import EO1Config
 from .evo1.configuration_evo1 import Evo1Config
-from .fastwam.configuration_fastwam import FastWAMConfig
-from .gaussian_actor.configuration_gaussian_actor import GaussianActorConfig
 from .groot.configuration_groot import GrootConfig
-from .lingbot_va.configuration_lingbot_va import LingBotVAConfig
-from .molmoact2.configuration_molmoact2 import MolmoAct2Config
-from .multi_task_dit.configuration_multi_task_dit import MultiTaskDiTConfig
-from .pi0.configuration_pi0 import PI0Config
-from .pi05.configuration_pi05 import PI05Config
 from .pretrained import PreTrainedPolicy
-from .smolvla.configuration_smolvla import SmolVLAConfig
-from .tdmpc.configuration_tdmpc import TDMPCConfig
 from .utils import validate_visual_features_consistency
-from .vla_jepa.configuration_vla_jepa import VLAJEPAConfig
-from .vqbet.configuration_vqbet import VQBeTConfig
-from .wall_x.configuration_wall_x import WallXConfig
-from .xvla.configuration_xvla import XVLAConfig
 
 
 def _reconnect_relative_absolute_steps(
@@ -88,100 +73,23 @@ def get_policy_class(name: str) -> type[PreTrainedPolicy]:
     """
     Retrieves a policy class by its registered name.
 
-    This function uses dynamic imports to avoid loading all policy classes into memory
-    at once, improving startup time and reducing dependencies.
+    Resolution is convention-based: the draccus-registered config class of ``name`` is
+    looked up, its ``configuration_*`` module path is rewritten to ``modeling_*``, and
+    the ``<X>Policy`` class is imported from there. The modeling module is only imported
+    at call time, keeping heavy optional dependencies lazy. This works for both built-in
+    policies and third-party lerobot plugins (anything registered via
+    ``@PreTrainedConfig.register_subclass``).
 
     Args:
-        name: The name of the policy. Supported names are "tdmpc", "diffusion", "act",
-            "multi_task_dit", "vqbet", "pi0", "pi05", "gaussian_actor", "smolvla", "wall_x",
-            "molmoact2", "eo1", "evo1".
+        name: The registered name of the policy (e.g. "act", "diffusion", "pi0").
     Returns:
         The policy class corresponding to the given name.
 
     Raises:
-        NotImplementedError: If the policy name is not recognized.
+        ValueError: If the policy name is not registered.
+        ImportError: If the policy's optional dependencies are not installed.
     """
-    if name == "tdmpc":
-        from .tdmpc.modeling_tdmpc import TDMPCPolicy
-
-        return TDMPCPolicy
-    elif name == "diffusion":
-        from .diffusion.modeling_diffusion import DiffusionPolicy
-
-        return DiffusionPolicy
-    elif name == "act":
-        from .act.modeling_act import ACTPolicy
-
-        return ACTPolicy
-    elif name == "multi_task_dit":
-        from .multi_task_dit.modeling_multi_task_dit import MultiTaskDiTPolicy
-
-        return MultiTaskDiTPolicy
-    elif name == "vqbet":
-        from .vqbet.modeling_vqbet import VQBeTPolicy
-
-        return VQBeTPolicy
-    elif name == "pi0":
-        from .pi0.modeling_pi0 import PI0Policy
-
-        return PI0Policy
-    elif name == "pi0_fast":
-        from .pi0_fast.modeling_pi0_fast import PI0FastPolicy
-
-        return PI0FastPolicy
-    elif name == "pi05":
-        from .pi05.modeling_pi05 import PI05Policy
-
-        return PI05Policy
-    elif name == "gaussian_actor":
-        from .gaussian_actor.modeling_gaussian_actor import GaussianActorPolicy
-
-        return GaussianActorPolicy
-    elif name == "smolvla":
-        from .smolvla.modeling_smolvla import SmolVLAPolicy
-
-        return SmolVLAPolicy
-    elif name == "groot":
-        from .groot.modeling_groot import GrootPolicy
-
-        return GrootPolicy
-    elif name == "xvla":
-        from .xvla.modeling_xvla import XVLAPolicy
-
-        return XVLAPolicy
-    elif name == "wall_x":
-        from .wall_x.modeling_wall_x import WallXPolicy
-
-        return WallXPolicy
-    elif name == "eo1":
-        from .eo1.modeling_eo1 import EO1Policy
-
-        return EO1Policy
-    elif name == "molmoact2":
-        from .molmoact2.modeling_molmoact2 import MolmoAct2Policy
-
-        return MolmoAct2Policy
-    elif name == "vla_jepa":
-        from .vla_jepa.modeling_vla_jepa import VLAJEPAPolicy
-
-        return VLAJEPAPolicy
-    elif name == "lingbot_va":
-        from .lingbot_va.modeling_lingbot_va import LingBotVAPolicy
-
-        return LingBotVAPolicy
-    elif name == "fastwam":
-        from .fastwam.modeling_fastwam import FastWAMPolicy
-
-        return FastWAMPolicy
-    elif name == "evo1":
-        from .evo1.modeling_evo1 import Evo1Policy
-
-        return Evo1Policy
-    else:
-        try:
-            return _get_policy_cls_from_policy_name(name=name)
-        except Exception as e:
-            raise ValueError(f"Policy type '{name}' is not available.") from e
+    return _get_policy_cls_from_policy_name(name=name)
 
 
 def make_policy_config(policy_type: str, **kwargs) -> PreTrainedConfig:
@@ -192,9 +100,8 @@ def make_policy_config(policy_type: str, **kwargs) -> PreTrainedConfig:
     mapping a string identifier to the corresponding config class.
 
     Args:
-        policy_type: The type of the policy. Supported types include "tdmpc",
-                     "multi_task_dit", "diffusion", "act", "vqbet", "pi0", "pi05", "gaussian_actor",
-                     "smolvla", "wall_x", "molmoact2", "eo1", "evo1".
+        policy_type: The registered type of the policy (any name registered via
+                     ``@PreTrainedConfig.register_subclass``, e.g. "act", "diffusion", "pi0").
         **kwargs: Keyword arguments to be passed to the configuration class constructor.
 
     Returns:
@@ -203,48 +110,11 @@ def make_policy_config(policy_type: str, **kwargs) -> PreTrainedConfig:
     Raises:
         ValueError: If the `policy_type` is not recognized.
     """
-    if policy_type == "tdmpc":
-        return TDMPCConfig(**kwargs)
-    elif policy_type == "diffusion":
-        return DiffusionConfig(**kwargs)
-    elif policy_type == "act":
-        return ACTConfig(**kwargs)
-    elif policy_type == "multi_task_dit":
-        return MultiTaskDiTConfig(**kwargs)
-    elif policy_type == "vqbet":
-        return VQBeTConfig(**kwargs)
-    elif policy_type == "pi0":
-        return PI0Config(**kwargs)
-    elif policy_type == "pi05":
-        return PI05Config(**kwargs)
-    elif policy_type == "gaussian_actor":
-        return GaussianActorConfig(**kwargs)
-    elif policy_type == "smolvla":
-        return SmolVLAConfig(**kwargs)
-    elif policy_type == "groot":
-        return GrootConfig(**kwargs)
-    elif policy_type == "xvla":
-        return XVLAConfig(**kwargs)
-    elif policy_type == "wall_x":
-        return WallXConfig(**kwargs)
-    elif policy_type == "eo1":
-        return EO1Config(**kwargs)
-    elif policy_type == "molmoact2":
-        return MolmoAct2Config(**kwargs)
-    elif policy_type == "vla_jepa":
-        return VLAJEPAConfig(**kwargs)
-    elif policy_type == "lingbot_va":
-        return LingBotVAConfig(**kwargs)
-    elif policy_type == "fastwam":
-        return FastWAMConfig(**kwargs)
-    elif policy_type == "evo1":
-        return Evo1Config(**kwargs)
-    else:
-        try:
-            config_cls = PreTrainedConfig.get_choice_class(policy_type)
-            return config_cls(**kwargs)
-        except Exception as e:
-            raise ValueError(f"Policy type '{policy_type}' is not available.") from e
+    try:
+        config_cls = PreTrainedConfig.get_choice_class(policy_type)
+    except Exception as e:
+        raise ValueError(f"Policy type '{policy_type}' is not available.") from e
+    return config_cls(**kwargs)
 
 
 class ProcessorConfigKwargs(TypedDict, total=False):
@@ -298,8 +168,7 @@ def make_pre_post_processors(
         A tuple containing the input (pre-processor) and output (post-processor) pipelines.
 
     Raises:
-        NotImplementedError: If a processor factory is not implemented for the given
-            policy configuration type.
+        ValueError: If no processor factory exists for the given policy configuration type.
     """
     if pretrained_path:
         if isinstance(policy_cfg, GrootConfig):
@@ -351,166 +220,13 @@ def make_pre_post_processors(
             )
         return preprocessor, postprocessor
 
-    # Create a new processor based on policy type
-    if isinstance(policy_cfg, TDMPCConfig):
-        from .tdmpc.processor_tdmpc import make_tdmpc_pre_post_processors
-
-        processors = make_tdmpc_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-        )
-
-    elif isinstance(policy_cfg, DiffusionConfig):
-        from .diffusion.processor_diffusion import make_diffusion_pre_post_processors
-
-        processors = make_diffusion_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-        )
-
-    elif isinstance(policy_cfg, ACTConfig):
-        from .act.processor_act import make_act_pre_post_processors
-
-        processors = make_act_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-        )
-
-    elif isinstance(policy_cfg, MultiTaskDiTConfig):
-        from .multi_task_dit.processor_multi_task_dit import (
-            make_multi_task_dit_pre_post_processors,
-        )
-
-        processors = make_multi_task_dit_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-        )
-
-    elif isinstance(policy_cfg, VQBeTConfig):
-        from .vqbet.processor_vqbet import make_vqbet_pre_post_processors
-
-        processors = make_vqbet_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-        )
-
-    elif isinstance(policy_cfg, PI0Config):
-        from .pi0.processor_pi0 import make_pi0_pre_post_processors
-
-        processors = make_pi0_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-        )
-
-    elif isinstance(policy_cfg, PI05Config):
-        from .pi05.processor_pi05 import make_pi05_pre_post_processors
-
-        processors = make_pi05_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-        )
-
-    elif isinstance(policy_cfg, GaussianActorConfig):
-        from .gaussian_actor.processor_gaussian_actor import make_gaussian_actor_pre_post_processors
-
-        processors = make_gaussian_actor_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-        )
-
-    elif isinstance(policy_cfg, SmolVLAConfig):
-        from .smolvla.processor_smolvla import make_smolvla_pre_post_processors
-
-        processors = make_smolvla_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-        )
-
-    elif isinstance(policy_cfg, GrootConfig):
-        from .groot.processor_groot import make_groot_pre_post_processors
-
-        processors = make_groot_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-            dataset_meta=kwargs.get("dataset_meta"),
-        )
-
-    elif isinstance(policy_cfg, XVLAConfig):
-        from .xvla.processor_xvla import (
-            make_xvla_pre_post_processors,
-        )
-
-        processors = make_xvla_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-        )
-
-    elif isinstance(policy_cfg, WallXConfig):
-        from .wall_x.processor_wall_x import make_wall_x_pre_post_processors
-
-        processors = make_wall_x_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-        )
-
-    elif isinstance(policy_cfg, EO1Config):
-        from .eo1.processor_eo1 import make_eo1_pre_post_processors
-
-        processors = make_eo1_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-        )
-    elif isinstance(policy_cfg, Evo1Config):
-        from .evo1.processor_evo1 import make_evo1_pre_post_processors
-
-        processors = make_evo1_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-        )
-
-    elif isinstance(policy_cfg, MolmoAct2Config):
-        from .molmoact2.processor_molmoact2 import make_molmoact2_pre_post_processors
-
-        processors = make_molmoact2_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-            dataset_meta=kwargs.get("dataset_meta"),
-        )
-
-    elif isinstance(policy_cfg, VLAJEPAConfig):
-        from .vla_jepa.processor_vla_jepa import make_vla_jepa_pre_post_processors
-
-        processors = make_vla_jepa_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-        )
-
-    elif isinstance(policy_cfg, LingBotVAConfig):
-        from .lingbot_va.processor_lingbot_va import make_lingbot_va_pre_post_processors
-
-        processors = make_lingbot_va_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-        )
-
-    elif isinstance(policy_cfg, FastWAMConfig):
-        from .fastwam.processor_fastwam import make_fastwam_pre_post_processors
-
-        processors = make_fastwam_pre_post_processors(
-            config=policy_cfg,
-            dataset_stats=kwargs.get("dataset_stats"),
-        )
-
-    else:
-        try:
-            processors = _make_processors_from_policy_config(
-                config=policy_cfg,
-                dataset_stats=kwargs.get("dataset_stats"),
-            )
-        except Exception as e:
-            raise ValueError(f"Processor for policy type '{policy_cfg.type}' is not implemented.") from e
-
-    return processors
+    # Create new processors from the policy config, resolving the per-policy factory
+    # function by naming convention (lazy import keeps optional dependencies optional).
+    return _make_processors_from_policy_config(
+        config=policy_cfg,
+        dataset_stats=kwargs.get("dataset_stats"),
+        dataset_meta=kwargs.get("dataset_meta"),
+    )
 
 
 def make_policy(
@@ -654,10 +370,12 @@ def make_policy(
     return policy
 
 
-def _get_policy_cls_from_policy_name(name: str) -> type[PreTrainedConfig]:
+def _get_policy_cls_from_policy_name(name: str) -> type[PreTrainedPolicy]:
     """Get policy class from its registered name using dynamic imports.
 
-    This is used as a helper function to import policies from 3rd party lerobot plugins.
+    Works for built-in policies and 3rd party lerobot plugins alike: the config class
+    registered under ``name`` is resolved via the draccus ChoiceRegistry, and the policy
+    class is imported from the sibling ``modeling_*`` module by naming convention.
 
     Args:
         name: The name of the policy.
@@ -683,22 +401,39 @@ def _get_policy_cls_from_policy_name(name: str) -> type[PreTrainedConfig]:
         "configuration_", "modeling_"
     )  # e.g., configuration_diffusion -> modeling_diffusion
 
-    module = importlib.import_module(module_path)
-    policy_cls = getattr(module, cls_name)
+    try:
+        module = importlib.import_module(module_path)
+    except ModuleNotFoundError as e:
+        if e.name == module_path:
+            # The modeling_* module itself does not exist for this policy type. A missing
+            # optional dependency inside an existing module propagates unchanged instead,
+            # so its actionable install hint stays visible.
+            raise ValueError(f"Policy class for '{name}' is not implemented.") from e
+        raise
+    policy_cls = getattr(module, cls_name, None)
+    if policy_cls is None:
+        raise ValueError(
+            f"Policy class '{cls_name}' not found in '{module_path}'. "
+            f"Policies must expose '<Name>Policy' in the sibling 'modeling_*' module by naming convention."
+        )
     return policy_cls
 
 
 def _make_processors_from_policy_config(
     config: PreTrainedConfig,
     dataset_stats: dict[str, dict[str, torch.Tensor]] | None = None,
+    dataset_meta: Any | None = None,
 ) -> tuple[Any, Any]:
     """Create pre- and post-processors from a policy configuration using dynamic imports.
 
-    This is used as a helper function to import processor factories from 3rd party lerobot plugins.
+    Resolves ``make_{type}_pre_post_processors`` from the policy's ``processor_*`` module
+    by naming convention. Works for built-in policies and 3rd party lerobot plugins.
 
     Args:
         config: The policy configuration object.
         dataset_stats: Dataset statistics for normalization.
+        dataset_meta: Dataset metadata, forwarded only to factories that declare a
+            ``dataset_meta`` parameter (e.g. groot, molmoact2).
     Returns:
         A tuple containing the input (pre-processor) and output (post-processor) pipelines.
     """
@@ -711,6 +446,19 @@ def _make_processors_from_policy_config(
     logging.debug(
         f"Instantiating pre/post processors using function '{function_name}' from module '{module_path}'"
     )
-    module = importlib.import_module(module_path)
-    function = getattr(module, function_name)
-    return function(config, dataset_stats=dataset_stats)
+    try:
+        module = importlib.import_module(module_path)
+    except ModuleNotFoundError as e:
+        if e.name == module_path:
+            # The processor_* module itself does not exist for this policy type. A missing
+            # optional dependency inside an existing module propagates unchanged instead,
+            # so its actionable install hint stays visible.
+            raise ValueError(f"Processor for policy type '{policy_type}' is not implemented.") from e
+        raise
+    function = getattr(module, function_name, None)
+    if function is None:
+        raise ValueError(f"Processor for policy type '{policy_type}' is not implemented.")
+    call_kwargs: dict[str, Any] = {"dataset_stats": dataset_stats}
+    if "dataset_meta" in inspect.signature(function).parameters:
+        call_kwargs["dataset_meta"] = dataset_meta
+    return function(config, **call_kwargs)

src/lerobot/policies/fastwam/processor_fastwam.py

@@ -22,20 +22,11 @@ import torch
 from lerobot.configs import PipelineFeatureType, PolicyFeature
 from lerobot.processor import (
     ActionProcessorStep,
-    AddBatchDimensionProcessorStep,
-    DeviceProcessorStep,
-    NormalizerProcessorStep,
     PolicyAction,
     PolicyProcessorPipeline,
     ProcessorStepRegistry,
-    RenameObservationsProcessorStep,
-    UnnormalizerProcessorStep,
-    policy_action_to_transition,
-    transition_to_policy_action,
-)
-from lerobot.utils.constants import (
-    POLICY_POSTPROCESSOR_DEFAULT_NAME,
-    POLICY_PREPROCESSOR_DEFAULT_NAME,
+    make_default_policy_processor_steps,
+    make_policy_processor_pipelines,
 )
 
 from .configuration_fastwam import FastWAMConfig
@@ -105,38 +96,20 @@ def make_fastwam_pre_post_processors(
     # anyway) and unsafe across fine-tuning: its `resize_size` would be inherited from the base
     # checkpoint's camera geometry, not this dataset's, making the concatenation N_cameras x too wide.
 
+    steps = make_default_policy_processor_steps(config, normalization_stats, normalizer_device=config.device)
+
     input_steps = [
-        RenameObservationsProcessorStep(rename_map={}),
-        AddBatchDimensionProcessorStep(),
-        DeviceProcessorStep(device=config.device),
-        NormalizerProcessorStep(
-            features={**config.input_features, **config.output_features},
-            norm_map=config.normalization_mapping,
-            stats=normalization_stats,
-            device=config.device,
-        ),
+        steps.rename_observations,
+        steps.add_batch_dim,
+        steps.to_device,
+        steps.normalize,
     ]
     output_steps = [
-        UnnormalizerProcessorStep(
-            features=config.output_features,
-            norm_map=config.normalization_mapping,
-            stats=normalization_stats,
-        ),
+        steps.unnormalize,
     ]
     if config.toggle_action_dimensions:
         output_steps.append(
             FastWAMActionToggleProcessorStep(toggle_dimensions=config.toggle_action_dimensions)
         )
-    output_steps.append(DeviceProcessorStep(device="cpu"))
-    return (
-        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
-            steps=input_steps,
-            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
-        ),
-        PolicyProcessorPipeline[PolicyAction, PolicyAction](
-            steps=output_steps,
-            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
-            to_transition=policy_action_to_transition,
-            to_output=transition_to_policy_action,
-        ),
-    )
+    output_steps.append(steps.to_cpu)
+    return make_policy_processor_pipelines(input_steps=input_steps, output_steps=output_steps)

src/lerobot/policies/gaussian_actor/processor_gaussian_actor.py

@@ -20,17 +20,10 @@ from typing import Any
 import torch
 
 from lerobot.processor import (
-    AddBatchDimensionProcessorStep,
-    DeviceProcessorStep,
-    NormalizerProcessorStep,
     PolicyAction,
     PolicyProcessorPipeline,
-    RenameObservationsProcessorStep,
-    UnnormalizerProcessorStep,
-    policy_action_to_transition,
-    transition_to_policy_action,
+    make_default_pre_post_processors,
 )
-from lerobot.utils.constants import POLICY_POSTPROCESSOR_DEFAULT_NAME, POLICY_PREPROCESSOR_DEFAULT_NAME
 
 from .configuration_gaussian_actor import GaussianActorConfig
 
@@ -62,33 +55,4 @@ def make_gaussian_actor_pre_post_processors(
     Returns:
         A tuple containing the configured pre-processor and post-processor pipelines.
     """
-
-    # Add remaining processors
-    input_steps = [
-        RenameObservationsProcessorStep(rename_map={}),
-        AddBatchDimensionProcessorStep(),
-        DeviceProcessorStep(device=config.device),
-        NormalizerProcessorStep(
-            features={**config.input_features, **config.output_features},
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-        ),
-    ]
-    output_steps = [
-        UnnormalizerProcessorStep(
-            features=config.output_features, norm_map=config.normalization_mapping, stats=dataset_stats
-        ),
-        DeviceProcessorStep(device="cpu"),
-    ]
-    return (
-        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
-            steps=input_steps,
-            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
-        ),
-        PolicyProcessorPipeline[PolicyAction, PolicyAction](
-            steps=output_steps,
-            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
-            to_transition=policy_action_to_transition,
-            to_output=transition_to_policy_action,
-        ),
-    )
+    return make_default_pre_post_processors(config, dataset_stats)

src/lerobot/policies/lingbot_va/processor_lingbot_va.py

@@ -25,19 +25,12 @@ import torch
 
 from lerobot.configs.types import FeatureType, NormalizationMode
 from lerobot.processor import (
-    AddBatchDimensionProcessorStep,
-    DeviceProcessorStep,
-    NormalizerProcessorStep,
     PolicyAction,
     PolicyProcessorPipeline,
     ProcessorStep,
-    RenameObservationsProcessorStep,
     UnnormalizerProcessorStep,
-)
-from lerobot.processor.converters import policy_action_to_transition, transition_to_policy_action
-from lerobot.utils.constants import (
-    POLICY_POSTPROCESSOR_DEFAULT_NAME,
-    POLICY_PREPROCESSOR_DEFAULT_NAME,
+    make_default_policy_processor_steps,
+    make_policy_processor_pipelines,
 )
 
 from .configuration_lingbot_va import LingBotVAConfig
@@ -52,15 +45,13 @@ def make_lingbot_va_pre_post_processors(
 ]:
     """Build the pre/post processor pipelines for LingBot-VA."""
 
+    steps = make_default_policy_processor_steps(config, dataset_stats)
+
     input_steps: list[ProcessorStep] = [
-        RenameObservationsProcessorStep(rename_map={}),
-        AddBatchDimensionProcessorStep(),
-        NormalizerProcessorStep(
-            features={**config.input_features, **config.output_features},
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-        ),
-        DeviceProcessorStep(device=config.device),
+        steps.rename_observations,
+        steps.add_batch_dim,
+        steps.normalize,
+        steps.to_device,
     ]
 
     # Unnormalize actions from [-1, 1] to physical units (QUANTILES) using q01/q99 restored from the checkpoint.
@@ -70,18 +61,7 @@ def make_lingbot_va_pre_post_processors(
             norm_map={FeatureType.ACTION: NormalizationMode.QUANTILES},
             stats=dataset_stats,
         ),
-        DeviceProcessorStep(device="cpu"),
+        steps.to_cpu,
     ]
 
-    return (
-        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
-            steps=input_steps,
-            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
-        ),
-        PolicyProcessorPipeline[PolicyAction, PolicyAction](
-            steps=output_steps,
-            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
-            to_transition=policy_action_to_transition,
-            to_output=transition_to_policy_action,
-        ),
-    )
+    return make_policy_processor_pipelines(input_steps=input_steps, output_steps=output_steps)

src/lerobot/policies/multi_task_dit/processor_multi_task_dit.py

@@ -19,18 +19,12 @@ from typing import Any
 import torch
 
 from lerobot.processor import (
-    AddBatchDimensionProcessorStep,
-    DeviceProcessorStep,
-    NormalizerProcessorStep,
     PolicyAction,
     PolicyProcessorPipeline,
-    RenameObservationsProcessorStep,
     TokenizerProcessorStep,
-    UnnormalizerProcessorStep,
-    policy_action_to_transition,
-    transition_to_policy_action,
+    make_default_policy_processor_steps,
+    make_policy_processor_pipelines,
 )
-from lerobot.utils.constants import POLICY_POSTPROCESSOR_DEFAULT_NAME, POLICY_PREPROCESSOR_DEFAULT_NAME
 
 from .configuration_multi_task_dit import MultiTaskDiTConfig
 
@@ -66,9 +60,11 @@ def make_multi_task_dit_pre_post_processors(
         A tuple containing the configured pre-processor and post-processor pipelines.
     """
 
+    steps = make_default_policy_processor_steps(config, dataset_stats, normalizer_device=config.device)
+
     input_steps = [
-        RenameObservationsProcessorStep(rename_map={}),
-        AddBatchDimensionProcessorStep(),
+        steps.rename_observations,
+        steps.add_batch_dim,
         TokenizerProcessorStep(
             tokenizer_name=config.text_encoder_name,
             padding=config.tokenizer_padding,
@@ -76,32 +72,12 @@ def make_multi_task_dit_pre_post_processors(
             max_length=config.tokenizer_max_length,
             truncation=config.tokenizer_truncation,
         ),
-        DeviceProcessorStep(device=config.device),
-        NormalizerProcessorStep(
-            features={**config.input_features, **config.output_features},
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-            device=config.device,
-        ),
+        steps.to_device,
+        steps.normalize,
     ]
     output_steps = [
-        UnnormalizerProcessorStep(
-            features=config.output_features,
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-        ),
-        DeviceProcessorStep(device="cpu"),
+        steps.unnormalize,
+        steps.to_cpu,
     ]
 
-    return (
-        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
-            steps=input_steps,
-            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
-        ),
-        PolicyProcessorPipeline[PolicyAction, PolicyAction](
-            steps=output_steps,
-            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
-            to_transition=policy_action_to_transition,
-            to_output=transition_to_policy_action,
-        ),
-    )
+    return make_policy_processor_pipelines(input_steps=input_steps, output_steps=output_steps)

src/lerobot/policies/pi0/processor_pi0.py

@@ -21,22 +21,16 @@ import torch
 from lerobot.configs import PipelineFeatureType, PolicyFeature
 from lerobot.processor import (
     AbsoluteActionsProcessorStep,
-    AddBatchDimensionProcessorStep,
     ComplementaryDataProcessorStep,
-    DeviceProcessorStep,
-    NormalizerProcessorStep,
     PolicyAction,
     PolicyProcessorPipeline,
     ProcessorStep,
     ProcessorStepRegistry,
     RelativeActionsProcessorStep,
-    RenameObservationsProcessorStep,
     TokenizerProcessorStep,
-    UnnormalizerProcessorStep,
-    policy_action_to_transition,
-    transition_to_policy_action,
+    make_default_policy_processor_steps,
+    make_policy_processor_pipelines,
 )
-from lerobot.utils.constants import POLICY_POSTPROCESSOR_DEFAULT_NAME, POLICY_PREPROCESSOR_DEFAULT_NAME
 
 from .configuration_pi0 import PI0Config
 
@@ -136,10 +130,12 @@ def make_pi0_pre_post_processors(
         action_names=getattr(config, "action_feature_names", None),
     )
 
+    steps = make_default_policy_processor_steps(config, dataset_stats)
+
     # OpenPI order: raw → relative → normalize → model → unnormalize → absolute
     input_steps: list[ProcessorStep] = [
-        RenameObservationsProcessorStep(rename_map={}),  # To mimic the same processor as pretrained one
-        AddBatchDimensionProcessorStep(),
+        steps.rename_observations,  # To mimic the same processor as pretrained one
+        steps.add_batch_dim,
         Pi0NewLineProcessor(),  # Add newlines before tokenization for PaliGemma
         TokenizerProcessorStep(
             tokenizer_name="google/paligemma-3b-pt-224",
@@ -147,32 +143,15 @@ def make_pi0_pre_post_processors(
             padding_side="right",
             padding="max_length",
         ),
-        DeviceProcessorStep(device=config.device),
+        steps.to_device,
         relative_step,
-        NormalizerProcessorStep(
-            features={**config.input_features, **config.output_features},
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-        ),
+        steps.normalize,
     ]
 
     output_steps: list[ProcessorStep] = [
-        UnnormalizerProcessorStep(
-            features=config.output_features, norm_map=config.normalization_mapping, stats=dataset_stats
-        ),
+        steps.unnormalize,
         AbsoluteActionsProcessorStep(enabled=config.use_relative_actions, relative_step=relative_step),
-        DeviceProcessorStep(device="cpu"),
+        steps.to_cpu,
     ]
 
-    return (
-        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
-            steps=input_steps,
-            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
-        ),
-        PolicyProcessorPipeline[PolicyAction, PolicyAction](
-            steps=output_steps,
-            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
-            to_transition=policy_action_to_transition,
-            to_output=transition_to_policy_action,
-        ),
-    )
+    return make_policy_processor_pipelines(input_steps=input_steps, output_steps=output_steps)

src/lerobot/policies/pi05/processor_pi05.py

@@ -24,26 +24,17 @@ import torch
 from lerobot.configs import PipelineFeatureType, PolicyFeature
 from lerobot.processor import (
     AbsoluteActionsProcessorStep,
-    AddBatchDimensionProcessorStep,
-    DeviceProcessorStep,
-    NormalizerProcessorStep,
     PolicyAction,
     PolicyProcessorPipeline,
     ProcessorStep,
     ProcessorStepRegistry,
     RelativeActionsProcessorStep,
-    RenameObservationsProcessorStep,
     TokenizerProcessorStep,
-    UnnormalizerProcessorStep,
-    policy_action_to_transition,
-    transition_to_policy_action,
+    make_default_policy_processor_steps,
+    make_policy_processor_pipelines,
 )
 from lerobot.types import EnvTransition, TransitionKey
-from lerobot.utils.constants import (
-    OBS_STATE,
-    POLICY_POSTPROCESSOR_DEFAULT_NAME,
-    POLICY_PREPROCESSOR_DEFAULT_NAME,
-)
+from lerobot.utils.constants import OBS_STATE
 
 from .configuration_pi05 import PI05Config
 
@@ -135,18 +126,16 @@ def make_pi05_pre_post_processors(
         action_names=getattr(config, "action_feature_names", None),
     )
 
+    steps = make_default_policy_processor_steps(config, dataset_stats)
+
     # OpenPI order: raw → relative → normalize → model → unnormalize → absolute
     input_steps: list[ProcessorStep] = [
-        RenameObservationsProcessorStep(rename_map={}),  # To mimic the same processor as pretrained one
-        AddBatchDimensionProcessorStep(),
+        steps.rename_observations,  # To mimic the same processor as pretrained one
+        steps.add_batch_dim,
         relative_step,
         # NOTE: NormalizerProcessorStep MUST come before Pi05PrepareStateTokenizerProcessorStep
         # because the tokenizer step expects normalized state in [-1, 1] range for discretization
-        NormalizerProcessorStep(
-            features={**config.input_features, **config.output_features},
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-        ),
+        steps.normalize,
         Pi05PrepareStateTokenizerProcessorStep(max_state_dim=config.max_state_dim),
         TokenizerProcessorStep(
             tokenizer_name="google/paligemma-3b-pt-224",
@@ -154,26 +143,13 @@ def make_pi05_pre_post_processors(
             padding_side="right",
             padding="max_length",
         ),
-        DeviceProcessorStep(device=config.device),
+        steps.to_device,
     ]
 
     output_steps: list[ProcessorStep] = [
-        UnnormalizerProcessorStep(
-            features=config.output_features, norm_map=config.normalization_mapping, stats=dataset_stats
-        ),
+        steps.unnormalize,
         AbsoluteActionsProcessorStep(enabled=config.use_relative_actions, relative_step=relative_step),
-        DeviceProcessorStep(device="cpu"),
+        steps.to_cpu,
     ]
 
-    return (
-        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
-            steps=input_steps,
-            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
-        ),
-        PolicyProcessorPipeline[PolicyAction, PolicyAction](
-            steps=output_steps,
-            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
-            to_transition=policy_action_to_transition,
-            to_output=transition_to_policy_action,
-        ),
-    )
+    return make_policy_processor_pipelines(input_steps=input_steps, output_steps=output_steps)

src/lerobot/policies/pi0_fast/processor_pi0_fast.py

@@ -25,26 +25,17 @@ from lerobot.configs import PipelineFeatureType, PolicyFeature
 from lerobot.processor import (
     AbsoluteActionsProcessorStep,
     ActionTokenizerProcessorStep,
-    AddBatchDimensionProcessorStep,
-    DeviceProcessorStep,
-    NormalizerProcessorStep,
     PolicyAction,
     PolicyProcessorPipeline,
     ProcessorStep,
     ProcessorStepRegistry,
     RelativeActionsProcessorStep,
-    RenameObservationsProcessorStep,
     TokenizerProcessorStep,
-    UnnormalizerProcessorStep,
-    policy_action_to_transition,
-    transition_to_policy_action,
+    make_default_policy_processor_steps,
+    make_policy_processor_pipelines,
 )
 from lerobot.types import EnvTransition, TransitionKey
-from lerobot.utils.constants import (
-    OBS_STATE,
-    POLICY_POSTPROCESSOR_DEFAULT_NAME,
-    POLICY_PREPROCESSOR_DEFAULT_NAME,
-)
+from lerobot.utils.constants import OBS_STATE
 
 from .configuration_pi0_fast import PI0FastConfig
 
@@ -135,6 +126,8 @@ def make_pi0_fast_pre_post_processors(
         action_names=getattr(config, "action_feature_names", None),
     )
 
+    steps = make_default_policy_processor_steps(config, dataset_stats)
+
     # Pi0Fast order: relative → normalize → tokenize → model → unnormalize → absolute
     # This matches pi0/pi0.5: RelativeActionsProcessorStep runs first on raw absolute actions,
     # caching the raw state. NormalizerProcessorStep then normalizes the raw relative actions,
@@ -144,14 +137,10 @@ def make_pi0_fast_pre_post_processors(
     # before Pi0FastPrepareStateAndLanguageTokenizerProcessorStep, so the state tokenizer
     # continues to receive normalized state in [-1, 1] as expected.
     input_steps: list[ProcessorStep] = [
-        RenameObservationsProcessorStep(rename_map={}),  # To mimic the same processor as pretrained one
-        AddBatchDimensionProcessorStep(),
+        steps.rename_observations,  # To mimic the same processor as pretrained one
+        steps.add_batch_dim,
         relative_step,
-        NormalizerProcessorStep(
-            features={**config.input_features, **config.output_features},
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-        ),
+        steps.normalize,
         Pi0FastPrepareStateAndLanguageTokenizerProcessorStep(max_state_dim=config.max_state_dim),
         TokenizerProcessorStep(
             tokenizer_name=config.text_tokenizer_name,
@@ -165,26 +154,13 @@ def make_pi0_fast_pre_post_processors(
             fast_skip_tokens=config.fast_skip_tokens,
             paligemma_tokenizer_name=config.text_tokenizer_name,
         ),
-        DeviceProcessorStep(device=config.device),
+        steps.to_device,
     ]
 
     output_steps: list[ProcessorStep] = [
-        UnnormalizerProcessorStep(
-            features=config.output_features, norm_map=config.normalization_mapping, stats=dataset_stats
-        ),
+        steps.unnormalize,
         AbsoluteActionsProcessorStep(enabled=config.use_relative_actions, relative_step=relative_step),
-        DeviceProcessorStep(device="cpu"),
+        steps.to_cpu,
     ]
 
-    return (
-        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
-            steps=input_steps,
-            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
-        ),
-        PolicyProcessorPipeline[PolicyAction, PolicyAction](
-            steps=output_steps,
-            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
-            to_transition=policy_action_to_transition,
-            to_output=transition_to_policy_action,
-        ),
-    )
+    return make_policy_processor_pipelines(input_steps=input_steps, output_steps=output_steps)

src/lerobot/policies/smolvla/processor_smolvla.py

@@ -19,19 +19,13 @@ from typing import Any
 import torch
 
 from lerobot.processor import (
-    AddBatchDimensionProcessorStep,
-    DeviceProcessorStep,
     NewLineTaskProcessorStep,
-    NormalizerProcessorStep,
     PolicyAction,
     PolicyProcessorPipeline,
-    RenameObservationsProcessorStep,
     TokenizerProcessorStep,
-    UnnormalizerProcessorStep,
-    policy_action_to_transition,
-    transition_to_policy_action,
+    make_default_policy_processor_steps,
+    make_policy_processor_pipelines,
 )
-from lerobot.utils.constants import POLICY_POSTPROCESSOR_DEFAULT_NAME, POLICY_PREPROCESSOR_DEFAULT_NAME
 
 from .configuration_smolvla import SmolVLAConfig
 
@@ -66,9 +60,11 @@ def make_smolvla_pre_post_processors(
         A tuple containing the configured pre-processor and post-processor pipelines.
     """
 
+    steps = make_default_policy_processor_steps(config, dataset_stats)
+
     input_steps = [
-        RenameObservationsProcessorStep(rename_map={}),  # To mimic the same processor as pretrained one
-        AddBatchDimensionProcessorStep(),
+        steps.rename_observations,  # To mimic the same processor as pretrained one
+        steps.add_batch_dim,
         NewLineTaskProcessorStep(),
         TokenizerProcessorStep(
             tokenizer_name=config.vlm_model_name,
@@ -76,28 +72,11 @@ def make_smolvla_pre_post_processors(
             padding_side="right",
             max_length=config.tokenizer_max_length,
         ),
-        DeviceProcessorStep(device=config.device),
-        NormalizerProcessorStep(
-            features={**config.input_features, **config.output_features},
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-        ),
+        steps.to_device,
+        steps.normalize,
     ]
     output_steps = [
-        UnnormalizerProcessorStep(
-            features=config.output_features, norm_map=config.normalization_mapping, stats=dataset_stats
-        ),
-        DeviceProcessorStep(device="cpu"),
+        steps.unnormalize,
+        steps.to_cpu,
     ]
-    return (
-        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
-            steps=input_steps,
-            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
-        ),
-        PolicyProcessorPipeline[PolicyAction, PolicyAction](
-            steps=output_steps,
-            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
-            to_transition=policy_action_to_transition,
-            to_output=transition_to_policy_action,
-        ),
-    )
+    return make_policy_processor_pipelines(input_steps=input_steps, output_steps=output_steps)

src/lerobot/policies/tdmpc/processor_tdmpc.py

@@ -19,17 +19,10 @@ from typing import Any
 import torch
 
 from lerobot.processor import (
-    AddBatchDimensionProcessorStep,
-    DeviceProcessorStep,
-    NormalizerProcessorStep,
     PolicyAction,
     PolicyProcessorPipeline,
-    RenameObservationsProcessorStep,
-    UnnormalizerProcessorStep,
-    policy_action_to_transition,
-    transition_to_policy_action,
+    make_default_pre_post_processors,
 )
-from lerobot.utils.constants import POLICY_POSTPROCESSOR_DEFAULT_NAME, POLICY_PREPROCESSOR_DEFAULT_NAME
 
 from .configuration_tdmpc import TDMPCConfig
 
@@ -61,32 +54,4 @@ def make_tdmpc_pre_post_processors(
     Returns:
         A tuple containing the configured pre-processor and post-processor pipelines.
     """
-
-    input_steps = [
-        RenameObservationsProcessorStep(rename_map={}),
-        AddBatchDimensionProcessorStep(),
-        DeviceProcessorStep(device=config.device),
-        NormalizerProcessorStep(
-            features={**config.input_features, **config.output_features},
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-        ),
-    ]
-    output_steps = [
-        UnnormalizerProcessorStep(
-            features=config.output_features, norm_map=config.normalization_mapping, stats=dataset_stats
-        ),
-        DeviceProcessorStep(device="cpu"),
-    ]
-    return (
-        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
-            steps=input_steps,
-            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
-        ),
-        PolicyProcessorPipeline[PolicyAction, PolicyAction](
-            steps=output_steps,
-            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
-            to_transition=policy_action_to_transition,
-            to_output=transition_to_policy_action,
-        ),
-    )
+    return make_default_pre_post_processors(config, dataset_stats)

src/lerobot/policies/vla_jepa/processor_vla_jepa.py

@@ -20,20 +20,16 @@ import torch
 
 from lerobot.policies.vla_jepa.configuration_vla_jepa import VLAJEPAConfig
 from lerobot.processor import (
-    AddBatchDimensionProcessorStep,
-    DeviceProcessorStep,
     EnvTransition,
-    NormalizerProcessorStep,
     PolicyAction,
     PolicyProcessorPipeline,
     ProcessorStep,
     ProcessorStepRegistry,
-    RenameObservationsProcessorStep,
     TransitionKey,
     UnnormalizerProcessorStep,
+    make_default_policy_processor_steps,
+    make_policy_processor_pipelines,
 )
-from lerobot.processor.converters import policy_action_to_transition, transition_to_policy_action
-from lerobot.utils.constants import POLICY_POSTPROCESSOR_DEFAULT_NAME, POLICY_PREPROCESSOR_DEFAULT_NAME
 
 
 @ProcessorStepRegistry.register(name="vla_jepa_clip_actions")
@@ -112,15 +108,12 @@ def make_vla_jepa_pre_post_processors(
     PolicyProcessorPipeline[PolicyAction, PolicyAction],
 ]:
     features = {**config.input_features, **config.output_features}
+    steps = make_default_policy_processor_steps(config, dataset_stats)
     input_steps = [
-        RenameObservationsProcessorStep(rename_map={}),
-        AddBatchDimensionProcessorStep(),
-        DeviceProcessorStep(device=config.device),
-        NormalizerProcessorStep(
-            features=features,
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-        ),
+        steps.rename_observations,
+        steps.add_batch_dim,
+        steps.to_device,
+        steps.normalize,
     ]
     output_steps: list[ProcessorStep] = []
     if config.clip_normalized_actions:
@@ -129,6 +122,8 @@ def make_vla_jepa_pre_post_processors(
         output_steps.append(
             PreSnapGripperProcessorStep(gripper_dim=config.gripper_dim, threshold=config.gripper_threshold)
         )
+    # NOTE: unlike the default policy unnormalizer (output features only), VLA-JEPA
+    # unnormalizes over BOTH input and output features.
     output_steps.append(
         UnnormalizerProcessorStep(
             features=features,
@@ -140,16 +135,5 @@ def make_vla_jepa_pre_post_processors(
         output_steps.append(
             BinarizeGripperProcessorStep(gripper_dim=config.gripper_dim, threshold=config.gripper_threshold)
         )
-    output_steps.append(DeviceProcessorStep(device="cpu"))
-    return (
-        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
-            steps=input_steps,
-            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
-        ),
-        PolicyProcessorPipeline[PolicyAction, PolicyAction](
-            steps=output_steps,
-            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
-            to_transition=policy_action_to_transition,
-            to_output=transition_to_policy_action,
-        ),
-    )
+    output_steps.append(steps.to_cpu)
+    return make_policy_processor_pipelines(input_steps=input_steps, output_steps=output_steps)

src/lerobot/policies/vqbet/processor_vqbet.py

@@ -20,17 +20,10 @@ from typing import Any
 import torch
 
 from lerobot.processor import (
-    AddBatchDimensionProcessorStep,
-    DeviceProcessorStep,
-    NormalizerProcessorStep,
     PolicyAction,
     PolicyProcessorPipeline,
-    RenameObservationsProcessorStep,
-    UnnormalizerProcessorStep,
-    policy_action_to_transition,
-    transition_to_policy_action,
+    make_default_pre_post_processors,
 )
-from lerobot.utils.constants import POLICY_POSTPROCESSOR_DEFAULT_NAME, POLICY_PREPROCESSOR_DEFAULT_NAME
 
 from .configuration_vqbet import VQBeTConfig
 
@@ -62,32 +55,4 @@ def make_vqbet_pre_post_processors(
     Returns:
         A tuple containing the configured pre-processor and post-processor pipelines.
     """
-
-    input_steps = [
-        RenameObservationsProcessorStep(rename_map={}),  # Let the possibility to the user to rename the keys
-        AddBatchDimensionProcessorStep(),
-        DeviceProcessorStep(device=config.device),
-        NormalizerProcessorStep(
-            features={**config.input_features, **config.output_features},
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-        ),
-    ]
-    output_steps = [
-        UnnormalizerProcessorStep(
-            features=config.output_features, norm_map=config.normalization_mapping, stats=dataset_stats
-        ),
-        DeviceProcessorStep(device="cpu"),
-    ]
-    return (
-        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
-            steps=input_steps,
-            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
-        ),
-        PolicyProcessorPipeline[PolicyAction, PolicyAction](
-            steps=output_steps,
-            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
-            to_transition=policy_action_to_transition,
-            to_output=transition_to_policy_action,
-        ),
-    )
+    return make_default_pre_post_processors(config, dataset_stats)

src/lerobot/policies/wall_x/processor_wall_x.py

@@ -20,19 +20,13 @@ import torch
 
 from lerobot.configs import PipelineFeatureType, PolicyFeature
 from lerobot.processor import (
-    AddBatchDimensionProcessorStep,
     ComplementaryDataProcessorStep,
-    DeviceProcessorStep,
-    NormalizerProcessorStep,
     PolicyAction,
     PolicyProcessorPipeline,
     ProcessorStepRegistry,
-    RenameObservationsProcessorStep,
-    UnnormalizerProcessorStep,
-    policy_action_to_transition,
-    transition_to_policy_action,
+    make_default_policy_processor_steps,
+    make_policy_processor_pipelines,
 )
-from lerobot.utils.constants import POLICY_POSTPROCESSOR_DEFAULT_NAME, POLICY_PREPROCESSOR_DEFAULT_NAME
 
 from .configuration_wall_x import WallXConfig
 
@@ -65,37 +59,22 @@ def make_wall_x_pre_post_processors(
         A tuple containing the configured pre-processor and post-processor pipelines
     """
 
+    steps = make_default_policy_processor_steps(config, dataset_stats)
+
     input_steps = [
-        RenameObservationsProcessorStep(rename_map={}),
-        AddBatchDimensionProcessorStep(),
+        steps.rename_observations,
+        steps.add_batch_dim,
         WallXTaskProcessor(),  # Process task description
-        NormalizerProcessorStep(
-            features={**config.input_features, **config.output_features},
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-        ),
-        DeviceProcessorStep(device=config.device),
+        steps.normalize,
+        steps.to_device,
     ]
 
     output_steps = [
-        UnnormalizerProcessorStep(
-            features=config.output_features, norm_map=config.normalization_mapping, stats=dataset_stats
-        ),
-        DeviceProcessorStep(device="cpu"),
+        steps.unnormalize,
+        steps.to_cpu,
     ]
 
-    return (
-        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
-            steps=input_steps,
-            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
-        ),
-        PolicyProcessorPipeline[PolicyAction, PolicyAction](
-            steps=output_steps,
-            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
-            to_transition=policy_action_to_transition,
-            to_output=transition_to_policy_action,
-        ),
-    )
+    return make_policy_processor_pipelines(input_steps=input_steps, output_steps=output_steps)
 
 
 @ProcessorStepRegistry.register(name="wall_x_task_processor")

src/lerobot/policies/xvla/processor_xvla.py

@@ -22,19 +22,14 @@ import torch
 
 from lerobot.configs import PipelineFeatureType, PolicyFeature
 from lerobot.processor import (
-    AddBatchDimensionProcessorStep,
-    DeviceProcessorStep,
-    NormalizerProcessorStep,
     ObservationProcessorStep,
     PolicyAction,
     PolicyProcessorPipeline,
     ProcessorStep,
     ProcessorStepRegistry,
-    RenameObservationsProcessorStep,
     TokenizerProcessorStep,
-    UnnormalizerProcessorStep,
-    policy_action_to_transition,
-    transition_to_policy_action,
+    make_default_policy_processor_steps,
+    make_policy_processor_pipelines,
 )
 from lerobot.types import EnvTransition, TransitionKey
 from lerobot.utils.constants import (
@@ -42,8 +37,6 @@ from lerobot.utils.constants import (
     OBS_IMAGES,
     OBS_PREFIX,
     OBS_STATE,
-    POLICY_POSTPROCESSOR_DEFAULT_NAME,
-    POLICY_PREPROCESSOR_DEFAULT_NAME,
 )
 
 from .configuration_xvla import XVLAConfig
@@ -61,10 +54,11 @@ def make_xvla_pre_post_processors(
     Build the LeRobot processor pipelines for XVLA.
     """
 
-    features = {**config.input_features, **config.output_features}
+    steps = make_default_policy_processor_steps(config, dataset_stats)
+
     input_steps = [
-        RenameObservationsProcessorStep(rename_map={}),
-        AddBatchDimensionProcessorStep(),
+        steps.rename_observations,
+        steps.add_batch_dim,
         TokenizerProcessorStep(
             tokenizer_name=config.tokenizer_name,
             max_length=config.tokenizer_max_length,
@@ -74,32 +68,15 @@ def make_xvla_pre_post_processors(
         XVLAImageToFloatProcessorStep(),
         XVLAImageNetNormalizeProcessorStep(),
         XVLAAddDomainIdProcessorStep(),
-        DeviceProcessorStep(device=config.device),
-        NormalizerProcessorStep(
-            features=features, norm_map=config.normalization_mapping, stats=dataset_stats
-        ),
+        steps.to_device,
+        steps.normalize,
     ]
     output_steps = [
-        UnnormalizerProcessorStep(
-            features=config.output_features,
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-        ),
-        DeviceProcessorStep(device="cpu"),
+        steps.unnormalize,
+        steps.to_cpu,
     ]
 
-    return (
-        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
-            steps=input_steps,
-            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
-        ),
-        PolicyProcessorPipeline[PolicyAction, PolicyAction](
-            steps=output_steps,
-            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
-            to_transition=policy_action_to_transition,
-            to_output=transition_to_policy_action,
-        ),
-    )
+    return make_policy_processor_pipelines(input_steps=input_steps, output_steps=output_steps)
 
 
 # Custom XVLA processor steps

src/lerobot/processor/__init__.py

@@ -42,10 +42,14 @@ from .delta_action_processor import MapDeltaActionToRobotActionStep, MapTensorTo
 from .device_processor import DeviceProcessorStep
 from .env_processor import IsaaclabArenaProcessorStep, LiberoProcessorStep
 from .factory import (
+    DefaultPolicyProcessorSteps,
+    make_default_policy_processor_steps,
+    make_default_pre_post_processors,
     make_default_processors,
     make_default_robot_action_processor,
     make_default_robot_observation_processor,
     make_default_teleop_action_processor,
+    make_policy_processor_pipelines,
 )
 from .gym_action_processor import (
     Numpy2TorchActionProcessorStep,
@@ -129,10 +133,14 @@ __all__ = [
     "ImageCropResizeProcessorStep",
     "InfoProcessorStep",
     "InterventionActionProcessorStep",
+    "DefaultPolicyProcessorSteps",
+    "make_default_policy_processor_steps",
+    "make_default_pre_post_processors",
     "make_default_processors",
     "make_default_teleop_action_processor",
     "make_default_robot_action_processor",
     "make_default_robot_observation_processor",
+    "make_policy_processor_pipelines",
     "AbsoluteActionsProcessorStep",
     "RelativeActionsProcessorStep",
     "MapDeltaActionToRobotActionStep",

src/lerobot/processor/factory.py

@@ -14,15 +14,33 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from lerobot.types import RobotAction, RobotObservation
+from dataclasses import dataclass
+from typing import Any
 
+import torch
+
+from lerobot.configs.policies import PreTrainedConfig
+from lerobot.types import PolicyAction, RobotAction, RobotObservation
+from lerobot.utils.constants import POLICY_POSTPROCESSOR_DEFAULT_NAME, POLICY_PREPROCESSOR_DEFAULT_NAME
+
+from .batch_processor import AddBatchDimensionProcessorStep
 from .converters import (
     observation_to_transition,
+    policy_action_to_transition,
     robot_action_observation_to_transition,
     transition_to_observation,
+    transition_to_policy_action,
     transition_to_robot_action,
 )
-from .pipeline import IdentityProcessorStep, RobotProcessorPipeline
+from .device_processor import DeviceProcessorStep
+from .normalize_processor import NormalizerProcessorStep, UnnormalizerProcessorStep
+from .pipeline import (
+    IdentityProcessorStep,
+    PolicyProcessorPipeline,
+    ProcessorStep,
+    RobotProcessorPipeline,
+)
+from .rename_processor import RenameObservationsProcessorStep
 
 
 def make_default_teleop_action_processor() -> RobotProcessorPipeline[
@@ -61,3 +79,97 @@ def make_default_processors():
     robot_action_processor = make_default_robot_action_processor()
     robot_observation_processor = make_default_robot_observation_processor()
     return (teleop_action_processor, robot_action_processor, robot_observation_processor)
+
+
+@dataclass
+class DefaultPolicyProcessorSteps:
+    """The canonical processor steps shared by most policies' pre/post pipelines.
+
+    Policies compose these in their own order (step ORDER is a Hub-serialized contract
+    and intentionally stays explicit per policy) and interleave their custom steps.
+    """
+
+    rename_observations: RenameObservationsProcessorStep
+    add_batch_dim: AddBatchDimensionProcessorStep
+    to_device: DeviceProcessorStep
+    normalize: NormalizerProcessorStep
+    unnormalize: UnnormalizerProcessorStep
+    to_cpu: DeviceProcessorStep
+
+
+def make_default_policy_processor_steps(
+    config: PreTrainedConfig,
+    dataset_stats: dict[str, dict[str, torch.Tensor]] | None = None,
+    *,
+    normalizer_device: torch.device | str | None = None,
+) -> DefaultPolicyProcessorSteps:
+    """Construct the canonical policy processor steps from a policy config.
+
+    Args:
+        config: A `PreTrainedConfig` providing `device`, `input_features`,
+            `output_features` and `normalization_mapping`.
+        dataset_stats: Dataset statistics used for (un)normalization.
+        normalizer_device: Device passed to `NormalizerProcessorStep` (some policies pin
+            their normalization stats to the policy device; most leave it unset).
+    """
+    return DefaultPolicyProcessorSteps(
+        rename_observations=RenameObservationsProcessorStep(rename_map={}),
+        add_batch_dim=AddBatchDimensionProcessorStep(),
+        to_device=DeviceProcessorStep(device=config.device),
+        normalize=NormalizerProcessorStep(
+            features={**config.input_features, **config.output_features},
+            norm_map=config.normalization_mapping,
+            stats=dataset_stats,
+            device=normalizer_device,
+        ),
+        unnormalize=UnnormalizerProcessorStep(
+            features=config.output_features, norm_map=config.normalization_mapping, stats=dataset_stats
+        ),
+        to_cpu=DeviceProcessorStep(device="cpu"),
+    )
+
+
+def make_policy_processor_pipelines(
+    input_steps: list[ProcessorStep],
+    output_steps: list[ProcessorStep],
+) -> tuple[
+    PolicyProcessorPipeline[dict[str, Any], dict[str, Any]],
+    PolicyProcessorPipeline[PolicyAction, PolicyAction],
+]:
+    """Wrap pre/post step lists into the canonical policy pipeline pair.
+
+    Uses the standard pipeline names (which determine the serialized JSON filenames on
+    the Hub) and the standard policy-action converters on the postprocessor.
+    """
+    return (
+        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
+            steps=input_steps,
+            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
+        ),
+        PolicyProcessorPipeline[PolicyAction, PolicyAction](
+            steps=output_steps,
+            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
+            to_transition=policy_action_to_transition,
+            to_output=transition_to_policy_action,
+        ),
+    )
+
+
+def make_default_pre_post_processors(
+    config: PreTrainedConfig,
+    dataset_stats: dict[str, dict[str, torch.Tensor]] | None = None,
+    *,
+    normalizer_device: torch.device | str | None = None,
+) -> tuple[
+    PolicyProcessorPipeline[dict[str, Any], dict[str, Any]],
+    PolicyProcessorPipeline[PolicyAction, PolicyAction],
+]:
+    """The pure-scaffold policy pipeline pair: Rename -> Batch -> Device -> Normalize,
+    and Unnormalize -> Device(cpu). Policies with custom steps or a different step order
+    compose `make_default_policy_processor_steps` themselves instead.
+    """
+    s = make_default_policy_processor_steps(config, dataset_stats, normalizer_device=normalizer_device)
+    return make_policy_processor_pipelines(
+        input_steps=[s.rename_observations, s.add_batch_dim, s.to_device, s.normalize],
+        output_steps=[s.unnormalize, s.to_cpu],
+    )

src/lerobot/processor/relative_action_processor.py

@@ -126,7 +126,7 @@ class RelativeActionsProcessorStep(ProcessorStep):
         observation = transition.get(TransitionKey.OBSERVATION, {})
         state = observation.get(OBS_STATE) if observation else None
 
-        # Always cache state for the paired AbsoluteActionsProcessorStep
+        # Always cache state for the paired AbsoluteActionsProcessorStep.
         if state is not None:
             self._last_state = state
 
@@ -146,6 +146,11 @@ class RelativeActionsProcessorStep(ProcessorStep):
         """Return the cached ``observation.state`` used as the reference point for relative/absolute action conversions."""
         return self._last_state
 
+    def set_cached_state(self, state: torch.Tensor | None) -> None:
+        """Override the cached anchor state, e.g. to re-pin a chunk's anchor after the
+        per-tick pipeline overwrote it (see ``SyncInferenceEngine``)."""
+        self._last_state = state
+
     def get_config(self) -> dict[str, Any]:
         return {
             "enabled": self.enabled,

src/lerobot/rollout/context.py

@@ -43,7 +43,6 @@ from lerobot.processor import (
     make_default_processors,
     rename_stats,
 )
-from lerobot.processor.relative_action_processor import RelativeActionsProcessorStep
 from lerobot.robots import make_robot_from_config
 from lerobot.teleoperators import Teleoperator, make_teleoperator_from_config
 from lerobot.utils.feature_utils import combine_feature_dicts, hw_to_dataset_features
@@ -52,7 +51,6 @@ from .configs import BaseStrategyConfig, DAggerStrategyConfig, RolloutConfig
 from .inference import (
     InferenceEngine,
     RTCInferenceConfig,
-    SyncInferenceConfig,
     create_inference_engine,
 )
 from .robot_wrapper import ThreadSafeRobot
@@ -399,15 +397,6 @@ def build_rollout_context(
         },
     )
 
-    if isinstance(cfg.inference, SyncInferenceConfig) and any(
-        isinstance(step, RelativeActionsProcessorStep) and step.enabled
-        for step in getattr(preprocessor, "steps", ())
-    ):
-        raise NotImplementedError(
-            "SyncInferenceEngine does not support policies with relative actions for now."
-            "Use --inference.type=rtc or remove relative action processor steps from the policy pipeline."
-        )
-
     # --- 7. Inference strategy (needs policy + pre/post + hardware) --
     logger.info(
         "Creating inference engine (type=%s)...",

src/lerobot/rollout/inference/sync.py

@@ -24,26 +24,21 @@ import torch
 
 from lerobot.policies.pretrained import PreTrainedPolicy
 from lerobot.policies.utils import make_robot_action, prepare_observation_for_inference
-from lerobot.processor import PolicyProcessorPipeline
+from lerobot.processor import PolicyProcessorPipeline, RelativeActionsProcessorStep
 
 from .base import InferenceEngine
 
 logger = logging.getLogger(__name__)
 
 
-# TODO(Steven): support relative-action policies.  The per-tick flow refreshes
-# ``RelativeActionsProcessorStep._last_state`` every call, so cached chunk
-# actions popped on later ticks get reanchored to the *current* robot state and
-# absolute targets drift through the chunk.  Relative-action policies are
-# rejected at context-build time today; RTC postprocesses the whole chunk and
-# is unaffected.
-#
-# Candidate fix: drive the policy via ``predict_action_chunk`` and serve a
-# local FIFO of postprocessed actions.  Eliminates drift by construction and
-# saves per-tick pre/post work, but bypasses ``select_action`` — needs
-# fallbacks for SAC (raises), ACT temporal ensembling (ensembler lives in
-# ``select_action``), and Diffusion-family (obs-history queues populated as a
-# side effect of ``select_action``).
+# Relative-action support: a predicted chunk of offsets is anchored to the robot
+# state at prediction time, but the sync engine reruns the pre/post pipeline every
+# tick, so ``RelativeActionsProcessorStep`` would re-anchor cached actions to the
+# current (moved) state and drift through the chunk. We pin the anchor per chunk:
+# a probe on the policy's public ``predict_action_chunk`` flags the ticks that
+# predict a fresh chunk; on the others the engine restores the anchor the relative
+# step overwrote. ``select_action`` stays on the hot path, so per-tick side effects
+# (e.g. LingBot-VA keyframe feedback) are preserved.
 
 
 class SyncInferenceEngine(InferenceEngine):
@@ -73,6 +68,31 @@ class SyncInferenceEngine(InferenceEngine):
         self._task = task
         self._device = torch.device(device or "cpu")
         self._robot_type = robot_type
+
+        # Find an enabled RelativeActionsProcessorStep to pin its anchor per chunk
+        # (see module comment), mirroring the RTC engine.
+        self._relative_step = next(
+            (
+                s
+                for s in getattr(preprocessor, "steps", ())
+                if isinstance(s, RelativeActionsProcessorStep) and s.enabled
+            ),
+            None,
+        )
+        # Set by the probe for the current tick / ever, respectively.
+        self._chunk_predicted = False
+        self._ever_predicted_chunk = False
+        self._original_predict_action_chunk = None  # set while the probe is installed
+        if self._relative_step is not None:
+            # ``action_names`` is optional on the step; fill it lazily from the
+            # policy/dataset so the relative<->absolute mask is built correctly. This is
+            # a deliberate engine->step side effect (the step is configured by its consumer).
+            if self._relative_step.action_names is None:
+                cfg_names = getattr(policy.config, "action_feature_names", None)
+                self._relative_step.action_names = list(cfg_names) if cfg_names else list(ordered_action_keys)
+            self._install_chunk_probe()
+            logger.info("Relative actions enabled: chunk anchor pinned per predicted chunk")
+
         logger.info(
             "SyncInferenceEngine initialized (device=%s, action_keys=%d)",
             self._device,
@@ -85,6 +105,11 @@ class SyncInferenceEngine(InferenceEngine):
 
     def stop(self) -> None:
         """No background resources to stop."""
+        # Undo the probe so the policy object isn't left permanently patched
+        # (it may outlive this engine or be reused by another).
+        if self._original_predict_action_chunk is not None:
+            self._policy.predict_action_chunk = self._original_predict_action_chunk
+            self._original_predict_action_chunk = None
         logger.info("SyncInferenceEngine stopped")
 
     def reset(self) -> None:
@@ -93,6 +118,27 @@ class SyncInferenceEngine(InferenceEngine):
         self._policy.reset()
         self._preprocessor.reset()
         self._postprocessor.reset()
+        # New episode: the next tick predicts a fresh chunk and re-anchors.
+        self._chunk_predicted = False
+        self._ever_predicted_chunk = False
+
+    def _install_chunk_probe(self) -> None:
+        """Wrap the policy's public ``predict_action_chunk`` so we learn which ticks
+        predict a fresh chunk (when the anchor must advance) without introspecting any
+        private action queue. Chunking policies call it from ``select_action``.
+
+        Wraps whatever callable is currently bound (e.g. an already-``torch.compile``d
+        one, since ``build_rollout_context`` compiles before building the engine); undone
+        in ``stop()``."""
+        self._original_predict_action_chunk = self._policy.predict_action_chunk
+        inner = self._original_predict_action_chunk
+
+        def probe(*args, **kwargs):
+            self._chunk_predicted = True
+            self._ever_predicted_chunk = True
+            return inner(*args, **kwargs)
+
+        self._policy.predict_action_chunk = probe
 
     def get_action(self, obs_frame: dict | None) -> torch.Tensor | None:
         """Run the full inference pipeline on ``obs_frame`` and return an action tensor."""
@@ -107,12 +153,25 @@ class SyncInferenceEngine(InferenceEngine):
             if self._device.type == "cuda" and self._policy.config.use_amp
             else nullcontext()
         )
+        # Snapshot the chunk anchor before the preprocessor overwrites it with this
+        # tick's state; restore it below if this tick only served a cached action.
+        # ``clone`` so the snapshot survives even if the cached tensor is ever mutated
+        # in place (today it is only rebound, but the copy is cheap for a state vector).
+        anchor_before = None
+        if self._relative_step is not None:
+            cached = self._relative_step.get_cached_state()
+            anchor_before = cached.clone() if cached is not None else None
+        self._chunk_predicted = False
         with torch.inference_mode(), autocast_ctx:
             observation = prepare_observation_for_inference(
                 observation, self._device, self._task, self._robot_type
             )
             observation = self._preprocessor(observation)
             action = self._policy.select_action(observation)
+            # Hold the anchor only for a chunking policy serving a cached action this
+            # tick; policies that never chunk or that recomputed keep refreshing.
+            if self._relative_step is not None and self._ever_predicted_chunk and not self._chunk_predicted:
+                self._relative_step.set_cached_state(anchor_before)
             action = self._postprocessor(action)
         action_tensor = action.squeeze(0).cpu()
 

tests/policies/test_relative_actions.py

@@ -346,3 +346,10 @@ def test_state_not_modified_by_relative_processor(dataset, action_dim):
 
     result_state = result[TransitionKey.OBSERVATION][OBS_STATE]
     torch.testing.assert_close(result_state, original_state)
+
+
+def test_cached_anchor_not_in_config():
+    """The cached anchor is ephemeral runtime state and must not leak into the config."""
+    step = RelativeActionsProcessorStep(enabled=True)
+    step.set_cached_state(torch.tensor([[1.0, 2.0, 3.0, 4.0]]))
+    assert set(step.get_config()) == {"enabled", "exclude_joints", "action_names"}

tests/test_rollout.py

@@ -348,3 +348,225 @@ def test_rollout_context_fields():
 
     field_names = {f.name for f in dataclasses.fields(RolloutContext)}
     assert field_names == {"runtime", "hardware", "policy", "processors", "data"}
+
+
+# ---------------------------------------------------------------------------
+# Sync engine: relative-action anchoring (drift-free chunk execution)
+# ---------------------------------------------------------------------------
+
+_REL_ACTION_NAMES = ["j0.pos", "j1.pos", "j2.pos", "gripper.pos"]
+_REL_ACTION_DIM = len(_REL_ACTION_NAMES)
+
+
+def _relative_pre_post(exclude_joints=None):
+    """Pre/post processors wrapping the real relative (caches anchor) and absolute
+    (relative + cached state) steps, mirroring what the sync engine feeds them."""
+    from lerobot.processor import (
+        AbsoluteActionsProcessorStep,
+        RelativeActionsProcessorStep,
+        TransitionKey,
+        create_transition,
+    )
+    from lerobot.utils.constants import OBS_STATE
+
+    relative_step = RelativeActionsProcessorStep(
+        enabled=True, exclude_joints=exclude_joints or [], action_names=list(_REL_ACTION_NAMES)
+    )
+    absolute_step = AbsoluteActionsProcessorStep(enabled=True, relative_step=relative_step)
+
+    class _Pre:
+        steps = [relative_step]
+
+        def __call__(self, observation):
+            # Run the relative step so it caches the anchor, then pass the batch through.
+            transition = create_transition(observation={OBS_STATE: observation[OBS_STATE]})
+            relative_step(transition)
+            return observation
+
+        def reset(self):
+            pass
+
+    class _Post:
+        def __call__(self, action):
+            transition = create_transition(action=action)
+            return absolute_step(transition)[TransitionKey.ACTION]
+
+        def reset(self):
+            pass
+
+    return _Pre(), _Post(), relative_step
+
+
+def _fake_relative_policy(chunk_rel, n_action_steps, chunking=True):
+    """Fake relative-action policy for the sync engine.
+
+    ``chunking=True`` buffers a chunk and serves it one action per tick, calling the
+    public ``predict_action_chunk`` only on refill (pi0/fastwam/lingbot). ``False``
+    returns an action directly and never calls it. The engine's anchor probe keys off
+    that public call, so the fake routes through it rather than any private queue.
+    """
+    from collections import deque
+
+    policy = MagicMock()
+    policy.config.use_amp = False
+    policy.config.action_feature_names = list(_REL_ACTION_NAMES)
+    state = {"predict_calls": 0}
+    queue = deque(maxlen=n_action_steps)
+
+    def predict_action_chunk(_batch=None, **_kwargs):
+        state["predict_calls"] += 1
+        return chunk_rel.unsqueeze(0)  # [B=1, n, dim]
+
+    def select_action(_observation):
+        if not chunking:
+            return chunk_rel[0].unsqueeze(0)
+        if len(queue) == 0:
+            actions = policy.predict_action_chunk(_observation)
+            queue.extend(actions.transpose(0, 1))  # [n, 1, dim]
+        return queue.popleft()
+
+    policy.predict_action_chunk.side_effect = predict_action_chunk
+    policy.select_action.side_effect = select_action
+    policy.reset.side_effect = queue.clear
+    policy._predict_state = state
+    return policy
+
+
+def _build_sync_engine(policy, pre, post):
+    from lerobot.rollout import SyncInferenceEngine
+
+    return SyncInferenceEngine(
+        policy=policy,
+        preprocessor=pre,
+        postprocessor=post,
+        dataset_features={"action": {"names": list(_REL_ACTION_NAMES)}},
+        ordered_action_keys=list(_REL_ACTION_NAMES),
+        task="test",
+        device="cpu",
+        robot_type="mock",
+    )
+
+
+def _obs_frame(state_values):
+    import numpy as np
+
+    return {"observation.state": np.asarray(state_values, dtype=np.float32)}
+
+
+def test_sync_relative_holds_anchor_across_chunk():
+    """Every action popped within a chunk must anchor to the tick-0 state (no drift)."""
+    n = 4
+    # A distinct relative offset per chunk step so a wrong anchor would be visible.
+    chunk_rel = torch.stack([torch.full((_REL_ACTION_DIM,), 0.1 * (i + 1)) for i in range(n)])
+    pre, post, relative_step = _relative_pre_post()
+    policy = _fake_relative_policy(chunk_rel, n_action_steps=n)
+    engine = _build_sync_engine(policy, pre, post)
+
+    assert engine._relative_step is relative_step  # introspection wired the step
+
+    s0 = [1.0, 2.0, 3.0, 4.0]
+    outputs = []
+    for tick in range(n):
+        # Feed a *different* state each tick; a drifting anchor would use it.
+        state = [v + tick for v in s0]
+        outputs.append(engine.get_action(_obs_frame(state)))
+
+    # Exactly one chunk was predicted across the n ticks.
+    assert policy._predict_state["predict_calls"] == 1
+    for tick in range(n):
+        expected = torch.tensor(s0) + chunk_rel[tick]
+        torch.testing.assert_close(outputs[tick], expected)
+
+    # Next tick empties the queue -> fresh chunk -> anchor advances to the new state.
+    s_next = [10.0, 20.0, 30.0, 40.0]
+    out = engine.get_action(_obs_frame(s_next))
+    assert policy._predict_state["predict_calls"] == 2
+    torch.testing.assert_close(out, torch.tensor(s_next) + chunk_rel[0])
+    # The anchor now reflects the fresh-chunk state, not the held one.
+    torch.testing.assert_close(relative_step.get_cached_state(), torch.tensor([s_next]))
+
+
+def test_sync_relative_reset_reanchors_new_episode():
+    """After ``reset()`` the first tick of the next episode anchors to the new state."""
+    n = 3
+    chunk_rel = torch.stack([torch.full((_REL_ACTION_DIM,), 0.2) for _ in range(n)])
+    pre, post, relative_step = _relative_pre_post()
+    policy = _fake_relative_policy(chunk_rel, n_action_steps=n)
+    engine = _build_sync_engine(policy, pre, post)
+
+    # Episode 1: one tick anchors to s0 and leaves cached actions in the queue.
+    engine.get_action(_obs_frame([1.0, 1.0, 1.0, 1.0]))
+    assert policy._predict_state["predict_calls"] == 1
+
+    engine.reset()  # clears the queue and the per-episode chunk flags
+
+    # Episode 2: a fresh state must produce a fresh chunk anchored to that state,
+    # not carry over the previous episode's anchor.
+    s_new = [7.0, 8.0, 9.0, 10.0]
+    out = engine.get_action(_obs_frame(s_new))
+    assert policy._predict_state["predict_calls"] == 2
+    torch.testing.assert_close(out, torch.tensor(s_new) + chunk_rel[0])
+    torch.testing.assert_close(relative_step.get_cached_state(), torch.tensor([s_new]))
+
+
+def test_sync_relative_non_chunking_policy_refreshes_every_tick():
+    """A policy that never calls ``predict_action_chunk`` must not freeze the anchor."""
+    n = 3
+    chunk_rel = torch.stack([torch.full((_REL_ACTION_DIM,), 0.5) for _ in range(n)])
+    pre, post, _ = _relative_pre_post()
+    policy = _fake_relative_policy(chunk_rel, n_action_steps=n, chunking=False)
+    engine = _build_sync_engine(policy, pre, post)
+
+    s0 = [1.0, 1.0, 1.0, 1.0]
+    for tick in range(3):
+        state = [v + tick for v in s0]
+        out = engine.get_action(_obs_frame(state))
+        # Anchor must track the current state every tick (no chunk => no hold).
+        torch.testing.assert_close(out, torch.tensor(state) + chunk_rel[0])
+    assert policy._predict_state["predict_calls"] == 0
+
+
+def test_sync_engine_no_relative_step_is_none():
+    """Without an enabled relative step, the engine takes the plain select_action path."""
+    policy = MagicMock()
+    policy.config.use_amp = False
+    engine = _build_sync_engine(policy, MagicMock(steps=[]), MagicMock())
+    assert engine._relative_step is None
+
+
+def test_sync_relative_exclude_joints_stay_absolute():
+    """With ``exclude_joints``, excluded dims pass through absolute while the relative
+    dims still hold the tick-0 anchor across the chunk."""
+    n = 4
+    # Distinct offset per step *and* per dim so a wrong anchor or a wrong mask shows up.
+    chunk_rel = torch.stack([torch.full((_REL_ACTION_DIM,), 0.1 * (i + 1)) for i in range(n)])
+    pre, post, relative_step = _relative_pre_post(exclude_joints=["gripper"])
+    policy = _fake_relative_policy(chunk_rel, n_action_steps=n)
+    engine = _build_sync_engine(policy, pre, post)
+
+    # gripper (last dim) is kept absolute; j0..j2 are relative.
+    mask = torch.tensor([1.0, 1.0, 1.0, 0.0])
+    s0 = [1.0, 2.0, 3.0, 4.0]
+    outputs = []
+    for tick in range(n):
+        state = [v + tick for v in s0]  # moving state; a drifting anchor would use it
+        outputs.append(engine.get_action(_obs_frame(state)))
+
+    assert policy._predict_state["predict_calls"] == 1  # one chunk held across n ticks
+    for tick in range(n):
+        # relative dims: anchor held at s0; excluded gripper dim: raw predicted value.
+        expected = chunk_rel[tick] + torch.tensor(s0) * mask
+        torch.testing.assert_close(outputs[tick], expected)
+
+
+def test_sync_relative_stop_restores_policy_method():
+    """``stop()`` un-patches the probe so the policy object isn't permanently modified."""
+    n = 3
+    chunk_rel = torch.stack([torch.full((_REL_ACTION_DIM,), 0.2) for _ in range(n)])
+    pre, post, _ = _relative_pre_post()
+    policy = _fake_relative_policy(chunk_rel, n_action_steps=n)
+    original = policy.predict_action_chunk
+    engine = _build_sync_engine(policy, pre, post)
+    assert policy.predict_action_chunk is not original  # probe installed
+    engine.stop()
+    assert policy.predict_action_chunk is original  # restored