refactor: rename body_name → base_name across backends and env configs

The parameter body_name was misleading — it refers specifically to the
floating base link, not an arbitrary body. Renamed everywhere:

- mujoco_backend, motrix_backend, motrix_numba_backend: constructor
  parameter body_name → base_name
- g1/base.py, go1/base.py, go2/base.py: Asset.body_name → base_name
- g1/joystick.py, g1/joystick_sac.py, go1/joystick.py, go2/joystick.py,
  g1/motion_tracking/tracking.py: call sites updated to base_name=
- motrix_backend._process_rigid_body_props: cfg.asset.body_name →
  cfg.asset.base_name
- tests/base/test_sim_backend.py: all body_name keys/kwargs updated

Author: TATP-233

src/unilab/base/backend/motrix_backend.py

@@ -21,7 +21,7 @@ def __init__(
         model_file: str,
         num_envs: int,
         sim_dt: float,
-        body_name: str = "base",
+        base_name: str = "base",
         np_dtype=np.float32,
         add_body_sensors: bool = False,
     ):
@@ -34,7 +34,7 @@ def __init__(
             from unilab.utils.xml_utils import inject_motrix_tracking_sensors
 
             tmp_path, _, valid_bnames = inject_motrix_tracking_sensors(
-                model_file, baselink_name=body_name
+                model_file, baselink_name=base_name
             )
             try:
                 self._model = mtx.load_model(tmp_path)  # pyright: ignore[reportPossiblyUnbound]
@@ -60,8 +60,8 @@ def __init__(
         self._np_dtype = np_dtype
 
         self._data = mtx.SceneData(self._model, batch=[num_envs])  # pyright: ignore[reportPossiblyUnbound]
-        self._body = self._model.get_body(body_name)
-        self._body_link = self._model.get_link(body_name)
+        self._body = self._model.get_body(base_name)
+        self._body_link = self._model.get_link(base_name)
         self._render_app: "RenderApp | None" = None
         self.backend_type = "motrix"
 
@@ -258,12 +258,12 @@ def _xyzw_to_wxyz(self, q: np.ndarray) -> np.ndarray:
 
     def _process_rigid_body_props(self, cfg) -> None:
         if cfg.domain_rand.randomize_base_mass:
-            mass = self._model.get_link(cfg.asset.body_name).get_mass_override(self._data)
+            mass = self._model.get_link(cfg.asset.base_name).get_mass_override(self._data)
             mass_low = cfg.domain_rand.added_mass_range[0]
             mass_high = cfg.domain_rand.added_mass_range[1]
             random_mass = mass + np.random.uniform(mass_low, mass_high, size=(self._num_envs,))
-            self._model.get_link(cfg.asset.body_name).set_mass_override(self._data, random_mass)
-            mass = self._model.get_link(cfg.asset.body_name).get_mass_override(self._data)
+            self._model.get_link(cfg.asset.base_name).set_mass_override(self._data, random_mass)
+            mass = self._model.get_link(cfg.asset.base_name).get_mass_override(self._data)
 
         if cfg.domain_rand.random_com:
             com_offset = np.zeros(
@@ -272,10 +272,10 @@ def _process_rigid_body_props(self, cfg) -> None:
             x_low = cfg.domain_rand.com_offset_x[0]
             x_high = cfg.domain_rand.com_offset_x[1]
             com_offset[:, 0] = np.random.uniform(x_low, x_high, self._num_envs)
-            self._model.get_link(cfg.asset.body_name).set_center_of_mass_override(
+            self._model.get_link(cfg.asset.base_name).set_center_of_mass_override(
                 self._data, com_offset
             )
-            self._model.get_link(cfg.asset.body_name).get_center_of_mass_override(self._data)
+            self._model.get_link(cfg.asset.base_name).get_center_of_mass_override(self._data)
 
     def push_robots(self, force_range):
         ex_force = np.random.rand(self.num_envs, 3) * 2 - 1  # [x_force, y_force, z_force]

src/unilab/base/backend/motrix_numba_backend.py

@@ -64,7 +64,7 @@ def __init__(
         model_file: str,
         num_envs: int,
         sim_dt: float,
-        body_name: str = "base",
+        base_name: str = "base",
         np_dtype=np.float32,
     ):
         if not MOTRIX_AVAILABLE:
@@ -76,7 +76,7 @@ def __init__(
         self._np_dtype = np_dtype
 
         self._data = mtx.SceneData(self._model, batch=[num_envs])
-        self._body = self._model.get_body(body_name)
+        self._body = self._model.get_body(base_name)
         self._render_app: "RenderApp | None" = None
 
     def step(self, ctrl: np.ndarray, nsteps: int = 1) -> None:

src/unilab/base/backend/mujoco_backend.py

@@ -18,7 +18,7 @@ def __init__(
         model_file: str,
         num_envs: int,
         sim_dt: float,
-        body_name: Optional[str] = None,
+        base_name: Optional[str] = None,
         np_dtype=None,
         add_body_sensors: bool = False,
     ):
@@ -28,7 +28,7 @@ def __init__(
             from unilab.utils.xml_utils import inject_mujoco_tracking_sensors
 
             tmp_path, self._tracked_body_ids, valid_bnames = inject_mujoco_tracking_sensors(
-                model_file, baselink_name=body_name
+                model_file, baselink_name=base_name
             )
             try:
                 self._model = mujoco.MjModel.from_xml_path(tmp_path)

src/unilab/envs/locomotion/g1/base.py

@@ -29,7 +29,7 @@ class ControlConfig:
 
 @dataclass
 class Asset:
-    body_name = "pelvis"
+    base_name = "pelvis"
     foot_name = "ankle_roll_link"
     ground = "floor"
 

src/unilab/envs/locomotion/g1/joystick.py

@@ -121,7 +121,7 @@ class G1JoystickPPO(G1BaseEnv):
 
     def __init__(self, cfg: G1JoystickPPOCfg, num_envs=1, backend_type="mujoco"):
         backend = create_backend(
-            backend_type, cfg.model_file, num_envs, cfg.sim_dt, body_name=cfg.asset.body_name
+            backend_type, cfg.model_file, num_envs, cfg.sim_dt, base_name=cfg.asset.base_name
         )
         super().__init__(cfg, backend, num_envs)
         self._enable_reward_log = True

src/unilab/envs/locomotion/g1/joystick_sac.py

@@ -114,7 +114,7 @@ class G1WalkTaskMjSAC(G1JoystickPPO):
 
     def __init__(self, cfg: G1JoystickSACCfg, num_envs=1, backend_type="mujoco"):
         backend = create_backend(
-            backend_type, cfg.model_file, num_envs, cfg.sim_dt, body_name=cfg.asset.body_name
+            backend_type, cfg.model_file, num_envs, cfg.sim_dt, base_name=cfg.asset.base_name
         )
         G1BaseEnv.__init__(self, cfg, backend, num_envs)
         self._enable_reward_log = True

src/unilab/envs/locomotion/g1/motion_tracking/tracking.py

@@ -138,7 +138,7 @@ def __init__(self, cfg: G1MotionTrackingCfg, num_envs=1, backend_type="mujoco"):
             raise ValueError("motion_file must be specified in config")
 
         backend = create_backend(
-            backend_type, cfg.model_file, num_envs, cfg.sim_dt, body_name=cfg.asset.body_name
+            backend_type, cfg.model_file, num_envs, cfg.sim_dt, base_name=cfg.asset.base_name
         )
         super().__init__(cfg, backend, num_envs)
 

src/unilab/envs/locomotion/go1/base.py

@@ -32,7 +32,7 @@ class ControlConfig:
 
 @dataclass
 class Asset:
-    body_name = "trunk"
+    base_name = "trunk"
     foot_name = "foot"
     ground = "floor"
 

src/unilab/envs/locomotion/go1/joystick.py

@@ -103,7 +103,7 @@ class Go1WalkTask(Go1BaseEnv):
 
     def __init__(self, cfg: Go1JoystickCfg, num_envs=1, backend_type="mujoco"):
         backend = create_backend(
-            backend_type, cfg.model_file, num_envs, cfg.sim_dt, body_name=cfg.asset.body_name
+            backend_type, cfg.model_file, num_envs, cfg.sim_dt, base_name=cfg.asset.base_name
         )
         super().__init__(cfg, backend, num_envs)
         self._enable_reward_log = True

src/unilab/envs/locomotion/go2/base.py

@@ -31,7 +31,7 @@ class ControlConfig:
 
 @dataclass
 class Asset:
-    body_name = "base"
+    base_name = "base"
     foot_name = "foot"
     ground = "floor"