SimReady Conform FET-003 Rigid Body Physics

Purpose

Use this workflow skill after FET000CORE and FET001BASENEUTRAL pass and the next profile validation gate is FET003BASENEUTRAL or FET003BASE_PHYSX. It brings a staged USD asset toward the SimReady rigid body physics contract while preserving visual hierarchy, physical scale, and source traceability.

This is an authoring and repair skill, not the final validator. Work on a staged copy under the requested output directory, rerun the same validation gate after each repair stage, and stop at the first remaining FET003 validation failure that needs user intent or upstream conversion data.

Prerequisites

Read the source-of-truth files named below before editing. Work on staged outputs where the skill requires them, and keep validation evidence with the result.

Source of Truth

Before changing an asset, load the exact FET003 manifest selected by the profile:

• nvcore/srspecs/docs/features/FET003baseneutral-0.1.0-rigidbody_physics.json
• nvcore/srspecs/docs/features/FET003basephysx-0.1.0-rigidbody_physics.json
• nvcore/srspecs/docs/features/FET003basephysx-0.2.0-rigidbody_physics.json
• nvcore/srspecs/docs/features/FET003-rigidbody_physics.md

Treat the selected JSON manifest as authoritative for the required IDs. If the markdown, manifest, validator, or report disagree on a requirement ID, follow the validation report for the current gate and call out the mismatch in the stage summary.

For per-requirement repair details, read references/fet003-requirements.md when a FET003 validation report or inspection identifies matching failures.

Inputs

Collect these before editing:

Instructions

Use this checklist when changing the repository:

1. Confirm the input asset exists and that FET000CORE and FET001BASE_NEUTRAL are already passing on the same staged asset. If they still fail, hand back to simready-foundation-conform-fet-000-core or simready-foundation-conform-fet-001-minimal first.
2. Parse the validation report and filter to FET003 failures. Do not repair later profile features such as FET004 multibody physics or FET005 grasp physics in this skill.
3. Load the selected FET003 manifest version and the requirement repair map.
4. Create a staged output folder under output_root; do not mutate the source unless the user explicitly asks for in-place repair.
5. Inspect the stage before editing:

- default prim, root prim, root xform ops, stage units, and composed bounds - existing UsdPhysics.RigidBodyAPI, CollisionAPI, MeshCollisionAPI, and MassAPI - mesh and Gprim candidates for collision geometry - instanceable prims, instance proxies, prototypes, nested rigid bodies, and skew or non-uniform scale - invisible or physics-only geometry purpose values - PhysX schemas and mesh-merge collections when a PhysX FET003 variant is selected

1. Decide the rigid-body model before authoring:

- Use one rigid body on the asset root or another clear xformable body root for simple movable props. - Use multiple rigid bodies only when the profile and asset structure clearly call for independent bodies. - Stop and hand off to FET004-oriented work when the asset needs articulated joints or multibody semantics.

1. Apply repairs in this order:

- Remove or relocate invalid rigid-body and collision APIs before adding new ones. - Apply UsdPhysics.RigidBodyAPI only to valid UsdGeomXformable body roots. - Apply UsdPhysicsCollisionAPI only to valid collider prims for the selected FET003 variant. - Apply UsdPhysicsMeshCollisionAPI only where allowed by the selected neutral or PhysX rule. - Author mass only from an explicit source or user-approved policy. - Fix instancing, nesting, skew, and non-uniform collider scale issues. - Mark invisible collision-only meshes with purpose = "guide".

1. Rerun the same profile validation gate, or the narrowest available FET003 validation gate.
2. Summarize the stage as passed, failed, skipped, or blocked. Stop when FET003 passes or the next FET003 failure requires source geometry, property prediction, mass data, collider intent, or a different feature skill.

Examples

Example request:

Repair FET003 rigid body physics failures on a prop USD asset.

Expected result summary:

staged_asset: repaired copy or output directory
validation: selected feature/profile gate and report path
remaining_failures: next failing requirement IDs, if any

Repair Policy

Make automatic repairs only when the intended result is mechanical and locally verifiable:

• Add UsdPhysics.RigidBodyAPI to a single xformable asset root when the asset is clearly a one-piece movable rigid body.
• Move CollisionAPI from an invalid Xform to a descendant Gprim only when that descendant is the clear collision representation.
• Add CollisionAPI to existing dedicated collider geometry when naming, purpose, or hierarchy clearly identifies it as collision geometry.
• Add MeshCollisionAPI to meshes only when mesh collision is the selected collider strategy and CollisionAPI is also present.
• Set purpose = "guide" on invisible collision-only mesh geometry.
• Remove RigidBodyAPI, CollisionAPI, or MeshCollisionAPI from invalid prims only when a valid replacement is authored in the same staged asset or the API is plainly accidental.
• Preserve the asset's composed physical size after any transform or scale repair.

Block and report instead of guessing when:

• The asset could be a static prop rather than a dynamic rigid body.
• Multiple plausible rigid body roots exist.
• Collision geometry must be generated from CAD/source data and no accepted collider strategy is available.
• Mass is missing and there is no explicit property source or user-approved default.
• De-instancing or baking transforms would change shared composition semantics.
• Nested rigid bodies likely indicate joints or articulation that belong to FET004.
• PhysX mesh merge is required but PhysX schemas or collection APIs are unavailable in the local environment.

Variant Guidance

For FET003BASENEUTRAL, prefer standard OpenUSD UsdPhysics schemas and avoid PhysX-only collider patterns. CollisionAPI belongs on UsdGeomGprim prims, and mesh-specific collision belongs on UsdGeomMesh prims that also have CollisionAPI.

For FET003BASEPHYSX, follow the selected manifest version. PhysX variants may allow CollisionAPI or MeshCollisionAPI on a mesh-merge Xform when PhysxMeshMergeCollisionAPI is applied and the collisionmeshes collection resolves to at least one Gprim. Do not use PhysX-only repairs for a neutral profile.

Validation Handoff

Preserve reports under the staged output directory. If the Physical AI Skill Hub validation commands are available, use the same profile gate that exposed the failure:

uv run --python 3.12 validate-simready-profile <staged-usd> \
  --profile <profile> \
  --profile-version <version> \
  --foundation-root <simready-foundation-root> \
  --foundation-spec-root <simready-foundation-root>/nv_core/sr_specs/docs \
  --report <output-root>/simready-profile-after-fet003.json

Count this skill as successful when the selected FET003 variant passes, even if the full profile still fails on later features. Report those remaining failures as handoff work for their own skills.

Limitations

• Do not silently mutate the source asset; work on the requested staged output.
• Do not hide later profile failures after the selected feature gate passes or fails.
• Do not invent geometry, metadata, or runtime behavior that conflicts with the asset intent.

Troubleshooting

• Error: validation tooling is unavailable. Solution: run the narrowest available USD or static check and report the gap.
• Error: a repair would change asset intent. Solution: stop and ask for direction or stage the smallest reversible edit.
• Error: later profile gates still fail. Solution: report the next failing feature and hand off to the matching conformance skill.

Resources

• assets/openai.yaml preserves optional UI metadata for clients that read skill display hints. It is not required for the workflow.
• references/ contains detailed requirement notes; load only the files needed for the active validation failure.

Summary Format

Report:

Keep the user-facing summary short: what rigid-body data changed, which FET003 variant was validated, what still fails, and the first validation gate that blocks progress.