feat(rl): consolidate HIL-SERL checkpoint into HF-style components

Make `RLAlgorithmConfig` and `RLAlgorithm` `HubMixin`s, add abstract
`state_dict()` / `load_state_dict()` for critic ensemble, target nets
and `log_alpha`, and persist them as a sibling `algorithm/` component
next to `pretrained_model/`. Replace the pickled `training_state.pt`
with an enriched `training_step.json` carrying `step` and
`interaction_step`, so resume restores actor + critics + target nets +
temperature + optimizers + RNG + counters from HF-standard files.

src/lerobot/rl/algorithms/base.py

@@ -15,25 +15,38 @@
 from __future__ import annotations
 
 import abc
+import builtins
+import os
 from collections.abc import Iterator
-from typing import TYPE_CHECKING, Any
+from pathlib import Path
+from typing import TYPE_CHECKING, Any, TypeVar
 
 import torch
+from huggingface_hub import hf_hub_download
+from huggingface_hub.constants import SAFETENSORS_SINGLE_FILE
+from huggingface_hub.errors import HfHubHTTPError
+from safetensors.torch import load_file as load_safetensors, save_file as save_safetensors
 from torch.optim import Optimizer
 
 from lerobot.types import BatchType
+from lerobot.utils.hub import HubMixin
 
 from .configs import RLAlgorithmConfig, TrainingStats
 
 if TYPE_CHECKING:
+    from torch import nn
+
     from ..data_sources.data_mixer import DataMixer
 
+T = TypeVar("T", bound="RLAlgorithm")
 
-class RLAlgorithm(abc.ABC):
+
+class RLAlgorithm(HubMixin, abc.ABC):
     """Base for all RL algorithms."""
 
     config_class: type[RLAlgorithmConfig]
     name: str
+    config: RLAlgorithmConfig
 
     @abc.abstractmethod
     def update(self, batch_iterator: Iterator[BatchType]) -> TrainingStats:
@@ -98,3 +111,97 @@ class RLAlgorithm(abc.ABC):
     def load_weights(self, weights: dict[str, Any], device: str | torch.device = "cpu") -> None:
         """Load policy state-dict received from the learner."""
         raise NotImplementedError
+
+    @abc.abstractmethod
+    def state_dict(self) -> dict[str, torch.Tensor]:
+        """Algorithm-owned trainable tensors.
+
+        Must return a flat tensor mapping for everything the algorithm owns
+        that is not part of the policy (e.g. critic ensembles, target networks,
+        temperature parameters). Algorithms with no training-only tensors
+        should explicitly return an empty dict.
+        """
+        raise NotImplementedError
+
+    @abc.abstractmethod
+    def load_state_dict(
+        self,
+        state_dict: dict[str, torch.Tensor],
+        device: str | torch.device = "cpu",
+    ) -> None:
+        """In-place load of algorithm-owned tensors.
+
+        Implementations MUST keep the identity of any ``nn.Parameter`` that an
+        optimizer references (e.g. SAC's ``log_alpha``) by using ``.copy_()``
+        rather than rebinding the attribute.
+        """
+        raise NotImplementedError
+
+    def _save_pretrained(self, save_directory: Path) -> None:
+        """Persist the algorithm's tensors and config to ``save_directory``.
+
+        Writes ``model.safetensors`` (algorithm tensors via :meth:`state_dict`)
+        and ``config.json`` (via :meth:`RLAlgorithmConfig.save_pretrained`).
+        """
+        tensors = {k: v.detach().cpu().contiguous() for k, v in self.state_dict().items()}
+        save_safetensors(tensors, str(save_directory / SAFETENSORS_SINGLE_FILE))
+        self.config._save_pretrained(save_directory)
+
+    @classmethod
+    def from_pretrained(
+        cls: builtins.type[T],
+        pretrained_name_or_path: str | Path,
+        *,
+        policy: nn.Module,
+        config: RLAlgorithmConfig | None = None,
+        force_download: bool = False,
+        resume_download: bool | None = None,
+        proxies: dict | None = None,
+        token: str | bool | None = None,
+        cache_dir: str | Path | None = None,
+        local_files_only: bool = False,
+        revision: str | None = None,
+        device: str | torch.device = "cpu",
+        **algo_kwargs: Any,
+    ) -> T:
+        """Build an algorithm and load its weights from ``pretrained_name_or_path``."""
+        if config is None:
+            config = cls.config_class.from_pretrained(
+                pretrained_name_or_path,
+                force_download=force_download,
+                resume_download=resume_download,
+                proxies=proxies,
+                token=token,
+                cache_dir=cache_dir,
+                local_files_only=local_files_only,
+                revision=revision,
+            )
+        if hasattr(config, "policy_config"):
+            config.policy_config = policy.config
+
+        instance = cls(policy=policy, config=config, **algo_kwargs)
+
+        model_id = str(pretrained_name_or_path)
+        if os.path.isdir(model_id):
+            model_file = os.path.join(model_id, SAFETENSORS_SINGLE_FILE)
+        else:
+            try:
+                model_file = hf_hub_download(
+                    repo_id=model_id,
+                    filename=SAFETENSORS_SINGLE_FILE,
+                    revision=revision,
+                    cache_dir=cache_dir,
+                    force_download=force_download,
+                    proxies=proxies,
+                    resume_download=resume_download,
+                    token=token,
+                    local_files_only=local_files_only,
+                )
+            except HfHubHTTPError as e:
+                raise FileNotFoundError(
+                    f"{SAFETENSORS_SINGLE_FILE} not found on the HuggingFace Hub in {model_id}"
+                ) from e
+
+        tensors = load_safetensors(model_file)
+        instance.load_state_dict(tensors, device=device)
+        return instance

src/lerobot/rl/algorithms/configs.py

@@ -15,10 +15,23 @@
 from __future__ import annotations
 
 import abc
+import builtins
+import logging
+import os
 from dataclasses import dataclass, field
-from typing import Any
+from pathlib import Path
+from typing import Any, TypeVar
 
 import draccus
+from huggingface_hub import hf_hub_download
+from huggingface_hub.constants import CONFIG_NAME
+from huggingface_hub.errors import HfHubHTTPError
+
+from lerobot.utils.hub import HubMixin
+
+T = TypeVar("T", bound="RLAlgorithmConfig")
+
+logger = logging.getLogger(__name__)
 
 
 @dataclass
@@ -43,7 +56,7 @@ class TrainingStats:
 
 
 @dataclass
-class RLAlgorithmConfig(draccus.ChoiceRegistry, abc.ABC):
+class RLAlgorithmConfig(draccus.ChoiceRegistry, HubMixin, abc.ABC):
     """Registry for algorithm configs."""
 
     @property
@@ -62,3 +75,64 @@ class RLAlgorithmConfig(draccus.ChoiceRegistry, abc.ABC):
         Must be overridden by every registered config subclass.
         """
         raise NotImplementedError(f"{cls.__name__} must implement from_policy_config()")
+
+    def _save_pretrained(self, save_directory: Path) -> None:
+        """Serialize this config as ``config.json`` inside ``save_directory``."""
+        with open(save_directory / CONFIG_NAME, "w") as f, draccus.config_type("json"):
+            draccus.dump(self, f, indent=4)
+
+    @classmethod
+    def from_pretrained(
+        cls: builtins.type[T],
+        pretrained_name_or_path: str | Path,
+        *,
+        force_download: bool = False,
+        resume_download: bool | None = None,
+        proxies: dict[Any, Any] | None = None,
+        token: str | bool | None = None,
+        cache_dir: str | Path | None = None,
+        local_files_only: bool = False,
+        revision: str | None = None,
+        **algo_kwargs: Any,
+    ) -> T:
+        model_id = str(pretrained_name_or_path)
+        config_file: str | None = None
+        if Path(model_id).is_dir():
+            if CONFIG_NAME in os.listdir(model_id):
+                config_file = os.path.join(model_id, CONFIG_NAME)
+            else:
+                logger.error(f"{CONFIG_NAME} not found in {Path(model_id).resolve()}")
+        else:
+            try:
+                config_file = hf_hub_download(
+                    repo_id=model_id,
+                    filename=CONFIG_NAME,
+                    revision=revision,
+                    cache_dir=cache_dir,
+                    force_download=force_download,
+                    proxies=proxies,
+                    resume_download=resume_download,
+                    token=token,
+                    local_files_only=local_files_only,
+                )
+            except HfHubHTTPError as e:
+                raise FileNotFoundError(
+                    f"{CONFIG_NAME} not found on the HuggingFace Hub in {model_id}"
+                ) from e
+
+        if config_file is None:
+            raise FileNotFoundError(f"{CONFIG_NAME} not found in {model_id}")
+
+        with draccus.config_type("json"):
+            instance = draccus.parse(RLAlgorithmConfig, config_file, args=[])
+
+        if cls is not RLAlgorithmConfig and not isinstance(instance, cls):
+            raise TypeError(
+                f"Config at {model_id} has type '{instance.type}' but was loaded via "
+                f"{cls.__name__}; use the matching subclass or RLAlgorithmConfig.from_pretrained()."
+            )
+
+        for key, value in algo_kwargs.items():
+            if hasattr(instance, key):
+                setattr(instance, key, value)
+        return instance

src/lerobot/rl/algorithms/sac/configuration_sac.py

@@ -16,6 +16,7 @@ from __future__ import annotations
 
 from dataclasses import dataclass, field
 
+from lerobot.configs.policies import PreTrainedConfig
 from lerobot.policies.gaussian_actor.configuration_gaussian_actor import (
     CriticNetworkConfig,
     GaussianActorConfig,
@@ -87,7 +88,7 @@ class SACAlgorithmConfig(RLAlgorithmConfig):
     use_torch_compile: bool = False
 
     # Policy config
-    policy_config: GaussianActorConfig | None = None
+    policy_config: PreTrainedConfig | None = None
 
     @classmethod
     def from_policy_config(cls, policy_cfg: GaussianActorConfig) -> SACAlgorithmConfig:

src/lerobot/rl/algorithms/sac/sac_algorithm.py

@@ -513,6 +513,46 @@ class SACAlgorithm(RLAlgorithm):
         """Load actor + discrete-critic weights into the policy."""
         self.policy.load_actor_weights(weights, device=device)
 
+    def state_dict(self) -> dict[str, torch.Tensor]:
+        """Algorithm-owned trainable tensors.
+
+        Encoder weights are stripped because they are owned by the policy
+        (``policy.encoder_critic``) and already saved via ``policy.save_pretrained``.
+        """
+        bundle: dict[str, torch.Tensor] = {}
+        for k, v in _strip_encoder_keys(self.critic_ensemble.state_dict()).items():
+            bundle[f"critic_ensemble.{k}"] = v
+        for k, v in _strip_encoder_keys(self.critic_target.state_dict()).items():
+            bundle[f"critic_target.{k}"] = v
+        if self.discrete_critic_target is not None:
+            for k, v in _strip_encoder_keys(self.discrete_critic_target.state_dict()).items():
+                bundle[f"discrete_critic_target.{k}"] = v
+        bundle["log_alpha"] = self.log_alpha.detach()
+        return bundle
+
+    def load_state_dict(
+        self,
+        state_dict: dict[str, torch.Tensor],
+        device: str | torch.device = "cpu",
+    ) -> None:
+        """In-place load of algorithm-owned tensors.
+
+        ``log_alpha`` is restored via ``Parameter.data.copy_`` so the
+        ``temperature`` optimizer's reference to the parameter object stays
+        valid after resume.
+        """
+        critic_ensemble_state = _split_prefix(state_dict, "critic_ensemble.")
+        critic_target_state = _split_prefix(state_dict, "critic_target.")
+        self.critic_ensemble.load_state_dict(critic_ensemble_state, strict=False)
+        self.critic_target.load_state_dict(critic_target_state, strict=False)
+
+        if self.discrete_critic_target is not None:
+            discrete_target_state = _split_prefix(state_dict, "discrete_critic_target.")
+            self.discrete_critic_target.load_state_dict(discrete_target_state, strict=False)
+
+        if "log_alpha" in state_dict:
+            self.log_alpha.data.copy_(state_dict["log_alpha"].to(self.log_alpha.device))
+
     def get_observation_features(
         self, observations: Tensor, next_observations: Tensor
     ) -> tuple[Tensor | None, Tensor | None]:
@@ -540,6 +580,16 @@ class SACAlgorithm(RLAlgorithm):
         return observation_features, next_observation_features
 
 
+def _strip_encoder_keys(state: dict[str, torch.Tensor]) -> dict[str, torch.Tensor]:
+    """Drop ``encoder.*`` keys from a critic-module state dict."""
+    return {k: v for k, v in state.items() if not k.startswith("encoder.")}
+
+
+def _split_prefix(state: dict[str, torch.Tensor], prefix: str) -> dict[str, torch.Tensor]:
+    """Return the subset of ``state`` whose keys start with ``prefix``, prefix-stripped."""
+    return {k.removeprefix(prefix): v for k, v in state.items() if k.startswith(prefix)}
+
+
 class CriticHead(nn.Module):
     def __init__(
         self,

src/lerobot/rl/learner.py

@@ -56,6 +56,8 @@ from pprint import pformat
 from typing import TYPE_CHECKING, Any
 
 import torch
+from huggingface_hub.constants import SAFETENSORS_SINGLE_FILE
+from safetensors.torch import load_file as load_safetensors
 from termcolor import colored
 from torch import nn
 from torch.multiprocessing import Queue
@@ -77,13 +79,16 @@ from lerobot.teleoperators import gamepad, so_leader  # noqa: F401
 from lerobot.teleoperators.utils import TeleopEvents
 from lerobot.utils.constants import (
     ACTION,
+    ALGORITHM_DIR,
     CHECKPOINTS_DIR,
     LAST_CHECKPOINT_LINK,
     PRETRAINED_MODEL_DIR,
     TRAINING_STATE_DIR,
+    TRAINING_STEP,
 )
 from lerobot.utils.device_utils import get_safe_torch_device
 from lerobot.utils.import_utils import _grpc_available, require_package
+from lerobot.utils.io_utils import load_json, write_json
 from lerobot.utils.process import ProcessSignalHandler
 from lerobot.utils.random_utils import set_seed
 from lerobot.utils.utils import (
@@ -370,7 +375,9 @@ def add_actor_information_and_train(
 
     # If we are resuming, we need to load the training state
     optimizers = algorithm.get_optimizers()
-    resume_optimization_step, resume_interaction_step = load_training_state(cfg=cfg, optimizers=optimizers)
+    resume_optimization_step, resume_interaction_step = load_training_state(
+        cfg=cfg, optimizers=optimizers, algorithm=algorithm, device=device
+    )
 
     logging.info("Starting learner thread")
     interaction_message = None
@@ -464,6 +471,7 @@ def add_actor_information_and_train(
                 policy=policy,
                 optimizers=optimizers,
                 replay_buffer=replay_buffer,
+                algorithm=algorithm,
                 offline_replay_buffer=offline_replay_buffer,
                 dataset_repo_id=dataset_repo_id,
                 fps=fps,
@@ -550,6 +558,7 @@ def save_training_checkpoint(
     policy: nn.Module,
     optimizers: dict[str, Optimizer],
     replay_buffer: ReplayBuffer,
+    algorithm: RLAlgorithm | None = None,
     offline_replay_buffer: ReplayBuffer | None = None,
     dataset_repo_id: str | None = None,
     fps: int = 30,
@@ -588,7 +597,7 @@ def save_training_checkpoint(
     # Create checkpoint directory
     checkpoint_dir = get_step_checkpoint_dir(cfg.output_dir, online_steps, optimization_step)
 
-    # Save checkpoint
+    # Save policy artifacts (pretrained_model/) + Trainer scaffolding (training_state/).
     save_checkpoint(
         checkpoint_dir=checkpoint_dir,
         step=optimization_step,
@@ -600,11 +609,18 @@ def save_training_checkpoint(
         postprocessor=postprocessor,
     )
 
-    # Save interaction step manually
-    training_state_dir = os.path.join(checkpoint_dir, TRAINING_STATE_DIR)
-    os.makedirs(training_state_dir, exist_ok=True)
-    training_state = {"step": optimization_step, "interaction_step": interaction_step}
-    torch.save(training_state, os.path.join(training_state_dir, "training_state.pt"))
+    # Algorithm-owned tensors live in their own component subfolder
+    # so they can be `push_to_hub`'d independently and don't bloat the inference artifact.
+    if algorithm is not None:
+        algorithm.save_pretrained(checkpoint_dir / ALGORITHM_DIR)
+
+    # Enrich training_step.json with the RL-specific interaction_step counter so
+    # both can be restored from a single file.
+    training_state_dir = checkpoint_dir / TRAINING_STATE_DIR
+    write_json(
+        {"step": optimization_step, "interaction_step": interaction_step},
+        training_state_dir / TRAINING_STEP,
+    )
 
     # Update the "last" symlink
     update_last_checkpoint(checkpoint_dir)
@@ -698,13 +714,20 @@ def handle_resume_logic(cfg: TrainRLServerPipelineConfig) -> TrainRLServerPipeli
 def load_training_state(
     cfg: TrainRLServerPipelineConfig,
     optimizers: Optimizer | dict[str, Optimizer],
+    algorithm: RLAlgorithm | None = None,
+    device: str | torch.device = "cpu",
 ):
     """
-    Loads the training state (optimizers, step count, etc.) from a checkpoint.
+    Loads the training state (optimizers, RNG, step + interaction step, and
+    algorithm-owned tensors) from the most recent checkpoint.
 
     Args:
-        cfg (TrainRLServerPipelineConfig): Training configuration
-        optimizers (Optimizer | dict): Optimizers to load state into
+        cfg: Training configuration.
+        optimizers: Optimizers to load state into.
+        algorithm: Algorithm whose state dict should be restored.
+            Required for full main-equivalent resume;
+            the policy itself is restored separately via ``make_policy``.
+        device: Device on which to place loaded algorithm tensors.
 
     Returns:
         tuple: (optimization_step, interaction_step) or (None, None) if not resuming
@@ -713,20 +736,31 @@ def load_training_state(
         return None, None
 
     # Construct path to the last checkpoint directory
-    checkpoint_dir = os.path.join(cfg.output_dir, CHECKPOINTS_DIR, LAST_CHECKPOINT_LINK)
+    checkpoint_dir = Path(cfg.output_dir) / CHECKPOINTS_DIR / LAST_CHECKPOINT_LINK
 
     logging.info(f"Loading training state from {checkpoint_dir}")
 
     try:
-        # Use the utility function from train_utils which loads the optimizer state
-        step, optimizers, _ = utils_load_training_state(Path(checkpoint_dir), optimizers, None)
+        # Restore optimizers + RNG + step from the standard `training_state/` folder
+        step, optimizers, _ = utils_load_training_state(checkpoint_dir, optimizers, None)
 
-        # Load interaction step separately from training_state.pt
-        training_state_path = os.path.join(checkpoint_dir, TRAINING_STATE_DIR, "training_state.pt")
-        interaction_step = 0
-        if os.path.exists(training_state_path):
-            training_state = torch.load(training_state_path, weights_only=False)  # nosec B614: Safe usage of torch.load
-            interaction_step = training_state.get("interaction_step", 0)
+        # Restore algorithm-owned tensors
+        if algorithm is not None:
+            algo_dir = checkpoint_dir / ALGORITHM_DIR
+            if algo_dir.is_dir():
+                tensors = load_safetensors(str(algo_dir / SAFETENSORS_SINGLE_FILE))
+                algorithm.load_state_dict(tensors, device=device)
+                logging.info(f"Loaded algorithm state from {algo_dir}")
+            else:
+                logging.warning(
+                    f"No algorithm state found at {algo_dir}; "
+                    "will keep their freshly-initialised values. Adam moments restored from the "
+                    "old optimizer state may not match these reset parameters."
+                )
+
+        # Read interaction_step from the enriched training_step.json
+        training_step_path = checkpoint_dir / TRAINING_STATE_DIR / TRAINING_STEP
+        interaction_step = int(load_json(training_step_path).get("interaction_step", 0))
 
         logging.info(f"Resuming from step {step}, interaction step {interaction_step}")
         return step, interaction_step

src/lerobot/utils/constants.py

@@ -47,6 +47,7 @@ CHECKPOINTS_DIR = "checkpoints"
 LAST_CHECKPOINT_LINK = "last"
 PRETRAINED_MODEL_DIR = "pretrained_model"
 TRAINING_STATE_DIR = "training_state"
+ALGORITHM_DIR = "algorithm"
 RNG_STATE = "rng_state.safetensors"
 TRAINING_STEP = "training_step.json"
 OPTIMIZER_STATE = "optimizer_state.safetensors"

tests/rl/test_sac_algorithm.py

@@ -515,3 +515,88 @@ def test_make_algorithm_builds_sac():
     algorithm = make_algorithm(cfg=algo_config, policy=policy)
     assert isinstance(algorithm, SACAlgorithm)
     assert algorithm.config.utd_ratio == 2
+
+
+# ===========================================================================
+# state_dict / load_state_dict (algorithm-side resume)
+# ===========================================================================
+
+
+def test_state_dict_contains_algorithm_owned_tensors():
+    """state_dict should pack critics, target networks, and log_alpha (no encoder bloat)."""
+    algorithm, _ = _make_algorithm()
+    sd = algorithm.state_dict()
+
+    assert "log_alpha" in sd
+    assert any(k.startswith("critic_ensemble.") for k in sd)
+    assert any(k.startswith("critic_target.") for k in sd)
+    # encoder weights live on the policy and must not be duplicated here.
+    assert not any(".encoder." in k for k in sd)
+
+
+def test_state_dict_includes_discrete_critic_target_when_present():
+    algorithm, _ = _make_algorithm(num_discrete_actions=3, action_dim=6)
+    sd = algorithm.state_dict()
+    assert any(k.startswith("discrete_critic_target.") for k in sd)
+
+
+def test_load_state_dict_round_trip_restores_critics_and_log_alpha():
+    """state_dict -> load_state_dict on a fresh algorithm restores all bytes exactly."""
+    sac_cfg = _make_sac_config(num_discrete_actions=3, action_dim=6)
+    src_policy = GaussianActorPolicy(config=sac_cfg)
+    src = SACAlgorithm(policy=src_policy, config=SACAlgorithmConfig.from_policy_config(sac_cfg))
+    src.make_optimizers_and_scheduler()
+    # Train a few steps so weights diverge from init (action_dim=7 = 6 continuous + 1 discrete).
+    src.update(_batch_iterator(action_dim=7))
+    src.update(_batch_iterator(action_dim=7))
+
+    dst_policy = GaussianActorPolicy(config=sac_cfg)
+    dst = SACAlgorithm(policy=dst_policy, config=SACAlgorithmConfig.from_policy_config(sac_cfg))
+    dst.make_optimizers_and_scheduler()
+
+    src_sd = src.state_dict()
+    dst.load_state_dict(src_sd)
+    dst_sd = dst.state_dict()
+
+    assert set(dst_sd) == set(src_sd)
+    for key in src_sd:
+        assert torch.allclose(src_sd[key].cpu(), dst_sd[key].cpu()), f"{key} mismatch after round-trip"
+
+
+def test_load_state_dict_preserves_log_alpha_parameter_identity():
+    """The temperature optimizer holds a reference to log_alpha; identity must survive load."""
+    algorithm, _ = _make_algorithm()
+    log_alpha_id_before = id(algorithm.log_alpha)
+    optimizer_param_id = id(algorithm.optimizers["temperature"].param_groups[0]["params"][0])
+    assert log_alpha_id_before == optimizer_param_id
+
+    new_state = algorithm.state_dict()
+    new_state["log_alpha"] = torch.tensor([0.42])
+    algorithm.load_state_dict(new_state)
+
+    assert id(algorithm.log_alpha) == log_alpha_id_before
+    assert id(algorithm.optimizers["temperature"].param_groups[0]["params"][0]) == log_alpha_id_before
+    assert torch.allclose(algorithm.log_alpha.detach().cpu(), torch.tensor([0.42]))
+
+
+def test_save_pretrained_round_trip_via_disk(tmp_path):
+    """End-to-end: save_pretrained -> from_pretrained restores tensors and config."""
+    sac_cfg = _make_sac_config()
+    src_policy = GaussianActorPolicy(config=sac_cfg)
+    src = SACAlgorithm(policy=src_policy, config=SACAlgorithmConfig.from_policy_config(sac_cfg))
+    src.make_optimizers_and_scheduler()
+    src.update(_batch_iterator())
+
+    save_dir = tmp_path / "algorithm"
+    src.save_pretrained(save_dir)
+    assert (save_dir / "model.safetensors").is_file()
+    assert (save_dir / "config.json").is_file()
+
+    dst_policy = GaussianActorPolicy(config=sac_cfg)
+    dst = SACAlgorithm.from_pretrained(save_dir, policy=dst_policy)
+
+    src_sd = src.state_dict()
+    dst_sd = dst.state_dict()
+    assert set(src_sd) == set(dst_sd)
+    for key in src_sd:
+        assert torch.allclose(src_sd[key].cpu(), dst_sd[key].cpu()), f"{key} mismatch after disk round-trip"

tests/rl/test_trainer.py

@@ -68,6 +68,12 @@ class _DummyRLAlgorithm(RLAlgorithm):
     def load_weights(self, weights, device="cpu") -> None:
         _ = (weights, device)
 
+    def state_dict(self) -> dict[str, torch.Tensor]:
+        return {}
+
+    def load_state_dict(self, state_dict, device="cpu") -> None:
+        _ = (state_dict, device)
+
 
 class _SimpleMixer:
     def get_iterator(self, batch_size: int, async_prefetch: bool = True, queue_size: int = 2):