[DO NOT MERGE] Example of adding articulated cart into Arena obj library

[xyao-nv]

Problem

The MobileShelvingCart USD asset has 9 rigid bodies (cart body + 4 swivels + 4 wheels) connected by joints, but was registered as ObjectType.RIGID with no ArticulationRootAPI baked into the USD. This caused two failures:

find_shallowest_rigid_body raised ValueError — found 9 rigid bodies at the same depth when expecting one
Isaac Lab's articulation initializer raised RuntimeError — no ArticulationRootAPI on the prim

Changes

New files (4)

isaaclab_arena/affordances/movable.py — Movable affordance for objects that can be pushed across the floor (carts, trolleys). Provides get_displacement(env) (XY Euclidean distance from initial position) and is_moved(env, threshold).

isaaclab_arena/utils/usd/spawners.py — Custom spawn function spawn_from_usd_and_add_articulation_root that wraps the standard USD spawner and calls schemas.define_articulation_root_properties to create the ArticulationRootAPI at spawn time for USDs that have joints but were authored without the API.

isaaclab_arena/tasks/move_object_task.py — MoveObjectTask extending TaskBase. Success is defined as XY displacement exceeding a configurable threshold. Includes MoveObjectTerminationsCfg with timeout + displacement-based success.

isaaclab_arena_environments/kitchen_move_object_environment.py — KitchenMoveObjectEnvironment example env with the kitchen background. Defaults to mobile_shelving_cart as the movable object. CLI args: --object, --embodiment, --displacement_threshold, --episode_length, --teleop_device.

Modified files (3)

isaaclab_arena/assets/object_library.py — MobileShelvingCart updated:

• Added Movable to class bases and "movable" to tags
• Set object_type = ObjectType.ARTICULATION
• Added spawn_cfg_addon with custom func pointing to the new spawner + ArticulationRootPropertiesCfg
• Added asset_cfg_addon with EMPTY_ARTICULATION_INIT_STATE_CFG
• Added init passing displacement_threshold to Movable
• Added Movable import at top of file

isaaclab_arena/tasks/terminations.py — Added object_displaced() termination function that measures XY displacement from initial position.

isaaclab_arena_environments/cli.py — Registered KitchenMoveObjectEnvironment in the ExampleEnvironments dict.