docs: update adding_benchmarks for async env changes

- Replace add_envs_task reference with env.call("task_description")
- Update use_async_envs default to True
- Add note about lazy GPU init for AsyncVectorEnv compatibility

Made-with: Cursor

docs/source/adding_benchmarks.mdx

@@ -26,7 +26,7 @@ During evaluation, data moves through four stages:
 1. gym.Env  ──→  raw observations (numpy dicts)
 
 2. Preprocessing  ──→  standard LeRobot keys + task description
-   (preprocess_observation, add_envs_task in envs/utils.py)
+   (preprocess_observation in envs/utils.py, env.call("task_description"))
 
 3. Processors  ──→  env-specific then policy-specific transforms
    (env_preprocessor, policy_preprocessor)
@@ -115,23 +115,22 @@ Each `EnvConfig` subclass declares two dicts that tell the policy what to expect
 ## Step by step
 
 <Tip>
-  At minimum, you need three files: a **gym.Env wrapper**, an **EnvConfig
-  subclass**, and a **factory dispatch branch**. Everything else is optional or
-  documentation.
+  At minimum, you need two files: a **gym.Env wrapper** and an **EnvConfig
+  subclass** with a `create_envs()` override. Everything else is optional or
+  documentation. No changes to `factory.py` are needed.
 </Tip>
 
 ### Checklist
 
-| File                                     | Required | Why                                       |
-| ---------------------------------------- | -------- | ----------------------------------------- |
-| `src/lerobot/envs/<benchmark>.py`        | Yes      | Wraps the simulator as a standard gym.Env |
-| `src/lerobot/envs/configs.py`            | Yes      | Registers your benchmark for the CLI      |
-| `src/lerobot/envs/factory.py`            | Yes      | Tells `make_env()` how to build your envs |
-| `src/lerobot/processor/env_processor.py` | Optional | Custom observation/action transforms      |
-| `src/lerobot/envs/utils.py`              | Optional | Only if you need new raw observation keys |
-| `pyproject.toml`                         | Yes      | Declares benchmark-specific dependencies  |
-| `docs/source/<benchmark>.mdx`            | Yes      | User-facing documentation page            |
-| `docs/source/_toctree.yml`               | Yes      | Adds your page to the docs sidebar        |
+| File                                     | Required | Why                                                          |
+| ---------------------------------------- | -------- | ------------------------------------------------------------ |
+| `src/lerobot/envs/<benchmark>.py`        | Yes      | Wraps the simulator as a standard gym.Env                    |
+| `src/lerobot/envs/configs.py`            | Yes      | Registers your benchmark and its `create_envs()` for the CLI |
+| `src/lerobot/processor/env_processor.py` | Optional | Custom observation/action transforms                         |
+| `src/lerobot/envs/utils.py`              | Optional | Only if you need new raw observation keys                    |
+| `pyproject.toml`                         | Yes      | Declares benchmark-specific dependencies                     |
+| `docs/source/<benchmark>.mdx`            | Yes      | User-facing documentation page                               |
+| `docs/source/_toctree.yml`               | Yes      | Adds your page to the docs sidebar                           |
 
 ### 1. The gym.Env wrapper (`src/lerobot/envs/<benchmark>.py`)
 
@@ -162,6 +161,8 @@ class MyBenchmarkEnv(gym.Env):
         ...
 ```
 
+**GPU-based simulators (e.g. MuJoCo with EGL rendering):** If your simulator allocates GPU/EGL contexts during `__init__`, defer that allocation to a `_ensure_env()` helper called on first `reset()`/`step()`. This avoids inheriting stale GPU handles when `AsyncVectorEnv` spawns worker processes. See `LiberoEnv._ensure_env()` for the pattern.
+
 Also provide a factory function that returns the nested dict structure:
 
 ```python
@@ -179,12 +180,15 @@ See `create_libero_envs()` (multi-suite, multi-task) and `create_metaworld_envs(
 
 ### 2. The config (`src/lerobot/envs/configs.py`)
 
-Register a config dataclass so users can select your benchmark with `--env.type=<name>`:
+Register a config dataclass so users can select your benchmark with `--env.type=<name>`. Each config owns its environment creation and processor logic via two methods:
+
+- **`create_envs(n_envs, use_async_envs)`** — Returns `{suite: {task_id: VectorEnv}}`. The base class default uses `gym.make()` for single-task envs. Multi-task benchmarks override this.
+- **`get_env_processors()`** — Returns `(preprocessor, postprocessor)`. The base class default returns identity (no-op) pipelines. Override if your benchmark needs observation/action transforms.
 
 ```python
 @EnvConfig.register_subclass("<benchmark_name>")
 @dataclass
-class MyBenchmarkEnv(EnvConfig):
+class MyBenchmarkEnvConfig(EnvConfig):
     task: str = "<default_task>"
     fps: int = <fps>
     obs_type: str = "pixels_agent_pos"
@@ -204,6 +208,20 @@ class MyBenchmarkEnv(EnvConfig):
     @property
     def gym_kwargs(self) -> dict:
         return {"obs_type": self.obs_type, "render_mode": self.render_mode}
+
+    def create_envs(self, n_envs: int, use_async_envs: bool = True):
+        """Override for multi-task benchmarks or custom env creation."""
+        from lerobot.envs.<benchmark> import create_<benchmark>_envs
+        return create_<benchmark>_envs(task=self.task, n_envs=n_envs, ...)
+
+    def get_env_processors(self):
+        """Override if your benchmark needs observation/action transforms."""
+        from lerobot.processor.pipeline import PolicyProcessorPipeline
+        from lerobot.processor.env_processor import MyBenchmarkProcessorStep
+        return (
+            PolicyProcessorPipeline(steps=[MyBenchmarkProcessorStep()]),
+            PolicyProcessorPipeline(steps=[]),
+        )
 ```
 
 Key points:
@@ -211,36 +229,11 @@ Key points:
 - The `register_subclass` name is what users pass on the CLI (`--env.type=<name>`).
 - `features` tells the policy what the environment produces.
 - `features_map` maps raw observation keys to LeRobot convention keys.
+- **No changes to `factory.py` needed** — the factory delegates to `cfg.create_envs()` and `cfg.get_env_processors()` automatically.
 
-### 3. The factory dispatch (`src/lerobot/envs/factory.py`)
+### 3. Env processor (optional — `src/lerobot/processor/env_processor.py`)
 
-Add a branch in `make_env()` to call your factory function:
-
-```python
-elif "<benchmark_name>" in cfg.type:
-    from lerobot.envs.<benchmark> import create_<benchmark>_envs
-
-    if cfg.task is None:
-        raise ValueError("<BenchmarkName> requires a task to be specified")
-
-    return create_<benchmark>_envs(
-        task=cfg.task,
-        n_envs=n_envs,
-        gym_kwargs=cfg.gym_kwargs,
-        env_cls=env_cls,
-    )
-```
-
-If your benchmark needs an env processor, add it in `make_env_pre_post_processors()`:
-
-```python
-if isinstance(env_cfg, MyBenchmarkEnv) or "<benchmark_name>" in env_cfg.type:
-    preprocessor_steps.append(MyBenchmarkProcessorStep())
-```
-
-### 4. Env processor (optional — `src/lerobot/processor/env_processor.py`)
-
-Only needed if your benchmark requires observation transforms beyond what `preprocess_observation()` handles (e.g. image flipping, coordinate conversion):
+Only needed if your benchmark requires observation transforms beyond what `preprocess_observation()` handles (e.g. image flipping, coordinate conversion). Define the processor step here and return it from `get_env_processors()` in your config (see step 2):
 
 ```python
 @dataclass
@@ -260,7 +253,7 @@ class MyBenchmarkProcessorStep(ObservationProcessorStep):
 
 See `LiberoProcessorStep` for a full example (image rotation, quaternion-to-axis-angle conversion).
 
-### 5. Dependencies (`pyproject.toml`)
+### 4. Dependencies (`pyproject.toml`)
 
 Add a new optional-dependency group:
 
@@ -281,11 +274,11 @@ Users install with:
 pip install -e ".[mybenchmark]"
 ```
 
-### 6. Documentation (`docs/source/<benchmark>.mdx`)
+### 5. Documentation (`docs/source/<benchmark>.mdx`)
 
 Write a user-facing page following the template in the next section. See `docs/source/libero.mdx` and `docs/source/metaworld.mdx` for full examples.
 
-### 7. Table of contents (`docs/source/_toctree.yml`)
+### 6. Table of contents (`docs/source/_toctree.yml`)
 
 Add your benchmark to the "Benchmarks" section:
 
@@ -302,6 +295,15 @@ Add your benchmark to the "Benchmarks" section:
   title: "Benchmarks"
 ```
 
+## Verifying your integration
+
+After completing the steps above, confirm that everything works:
+
+1. **Install** — `pip install -e ".[mybenchmark]"` and verify the dependency group installs cleanly.
+2. **Smoke test env creation** — call `make_env()` with your config in Python, check that the returned dict has the expected `{suite: {task_id: VectorEnv}}` shape, and that `reset()` returns observations with the right keys.
+3. **Run a full eval** — `lerobot-eval --env.type=<name> --env.task=<task> --eval.n_episodes=1 --eval.batch_size=1 --policy.path=<any_compatible_policy>` to exercise the full pipeline end-to-end.
+4. **Check success detection** — verify that `info["is_success"]` flips to `True` when the task is actually completed. This is what the eval loop uses to compute success rates.
+
 ## Writing a benchmark doc page
 
 Each benchmark `.mdx` page should include: