[Proposal] Remove deformable registry; spawn deformables via Newton import_usd

[mmichelis]

Proposal

Remove the deformable registry in isaaclab_contrib and spawn deformables in Newton directly through Newton's import_usd/add_usd, the same way rigid bodies are ingested today.

Motivation

Deformables currently bypass Newton's USD importer. Instead, IsaacLab maintains a parallel registry:

• DeformableRegistryEntry dataclass + NewtonManager._deformable_registry — source/isaaclab_contrib/isaaclab_contrib/deformable/deformable_object.py:38
• Populated by _register_deformable(), which hand-reads the USD mesh/material into an entry — deformable_object.py:634
• Consumed by instantiate_builder_from_stage() overrides that ignore_paths the deformable meshes in add_usd and re-inject them via add_deformable_entry_to_builder() — vbd_manager.py:160, coupled_mjwarp_vbd_manager.py, coupled_featherstone_vbd_manager.py

This is an explicit workaround. The TODOs say so:

"Subclass should not override this method, once deformables supported on Newton import_usd, this can be unified with NewtonManager's implementation." — vbd_manager.py:168 (and the same in both coupled managers)

By contrast, rigid bodies need no registry — NewtonManager.instantiate_builder_from_stage() just calls builder.add_usd(stage) (source/isaaclab_newton/isaaclab_newton/physics/newton_manager.py:1029).

The upstream Newton work to make import_usd handle deformables is in progress:

• Add Newton Importer Support for USD Deformable Physics Schemas newton-physics/newton#3178 — Add Newton Importer Support for USD Deformable Physics Schemas (release-blocking)
• [REQ] Surface Deformable Parsing through USD in Newton Builder newton-physics/newton#3036 — Surface Deformable Parsing through USD in Newton Builder
• [REQ] Per-Body Indexing for Volume Deformables with Material Loaded from USD newton-physics/newton#3038 — Per-Body Indexing for Volume Deformables with Material Loaded from USD

Once these land, the registry, the _register_deformable() reader, the ignore_paths plumbing, and the instantiate_builder_from_stage() overrides can all be deleted, unifying the deformable path with the rigid-body path.

Alternatives

Keep the registry indefinitely — rejected: it duplicates Newton's importer, diverges from the rigid-body path, and is maintenance overhead across three manager subclasses.

Build Info

• Isaac Lab Version: develop (3.x)
• Isaac Sim Version: 5.x / Newton backend

Additional context

Depends on the Newton importer work above. Related: #6207 (removing Kit/omni.physx reliance from deformable spawning).

Checklist

• I have checked that there is no similar issue in the repo (required)

Acceptance Criteria

• Newton import_usd/add_usd ingests deformables natively (blocked on Add Newton Importer Support for USD Deformable Physics Schemas newton-physics/newton#3178, [Bug Report] No module named 'carb._carb' #3036, [Bug Report] Bug title #3038).
• DeformableRegistryEntry, _deformable_registry, _register_deformable(), and add_deformable_entry_to_builder() are removed.
• instantiate_builder_from_stage() overrides and _get_deformable_ignore_paths() are dropped; deformable managers reuse NewtonManager's implementation.

[RandomOakForest]

Thanks for this proposal as well. The team will review it.