Adding Collision USD data classes and writers

[vidurv-nvidia]

Description

Adds the collision schema-fragment API: a prim can carry collision properties from multiple USD namespaces (UsdPhysics + PhysX + Newton) at once, and core names no backend.

• CollisionFragment marker + UsdPhysicsCollisionCfg (physics:collisionEnabled; UsdPhysics.CollisionAPI anchor) in isaaclab.
• PhysxCollisionCfg (physxCollision:* — contact_offset, rest_offset, torsional_patch_radius, min_torsional_patch_radius) in isaaclab_physx.
• NewtonCollisionCfg (newton:*) in isaaclab_newton.
• apply_collision_properties family writer (applies the anchor, then dispatches each fragment via its func; core imports no backend).
• The spawner collision_props slot now also accepts a CollisionFragment / list[CollisionFragment].

This PR is purely additive and self-contained: it builds only on the single-namespace schema-fragment base (SchemaFragment + apply_namespaced) already in develop, existing call sites are untouched (a transition bridge routes legacy single cfgs to the existing define_/modify_ writers), and it does not depend on any other open PR.

Type of change

• New feature (non-breaking change which adds functionality)

Screenshots

N/A — non-visual API change.

Checklist

• I have read and understood the contribution guidelines
• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have added a changelog fragment under source/<pkg>/changelog.d/ for every touched package (do not edit CHANGELOG.rst or bump extension.toml — CI handles that)
• I have added my name to the CONTRIBUTORS.md or my name already exists there

[greptile-apps]

Greptile Summary

Adds the collision schema-fragment family (CollisionFragment, UsdPhysicsCollisionCfg, PhysxCollisionCfg, NewtonCollisionCfg) and the apply_collision_properties writer, mirroring the rigid-body fragment structure from #5976. Spawner and converter collision_props slots are widened to also accept a fragment list, with a transition shim that routes new fragment lists to apply_collision_properties and legacy single cfgs to the existing writers unchanged.

• New config classes: CollisionFragment marker in core; UsdPhysicsCollisionCfg (physics:collisionEnabled), PhysxCollisionCfg (physxCollision:*), and NewtonCollisionCfg (newton:*) each carry _usd_namespace/_usd_applied_schema metadata consumed by the shared apply_namespaced dispatcher.
• Writer: apply_collision_properties applies UsdPhysics.CollisionAPI as the implicit anchor then dispatches each fragment; it differs from its rigid-body counterpart in that it omits the prim-validity guard and always returns True (flagged previously).
• Transition shims: Identical 5-line routing blocks are duplicated in four spawner/converter files; all carry a # remove later note acknowledging the tech debt.

Confidence Score: 5/5

Safe to merge; the change is additive and all existing call sites continue to work through the transition bridge.

The fragment classes, the apply_collision_properties writer, and the transition shims are all strictly additive. Legacy collision_props call sites are untouched in the else-branch of every shim. The only open concern (missing prim-validity guard and always-True return in apply_collision_properties) was raised in a prior review round; no new issues of that kind appear in this diff.

source/isaaclab/isaaclab/sim/schemas/schemas.py — apply_collision_properties still lacks the prim-validity guard present in its rigid-body counterpart (flagged in a prior review).

Important Files Changed

Filename	Overview
source/isaaclab/isaaclab/sim/schemas/schemas.py	Adds apply_collision_properties; missing prim validity guard and always-True return (previously flagged) relative to the apply_rigid_body_properties mirror function
source/isaaclab/isaaclab/sim/schemas/schemas_cfg.py	Adds CollisionFragment marker and UsdPhysicsCollisionCfg; mirrors RigidBodyFragment/UsdPhysicsRigidBodyCfg structure cleanly
source/isaaclab_physx/isaaclab_physx/sim/schemas/schemas_cfg.py	Adds PhysxCollisionCfg with correct _usd_namespace/applied_schema metadata for physxCollision namespace; fields align with PhysxCollisionAPI attributes
source/isaaclab_newton/isaaclab_newton/sim/schemas/schemas_cfg.py	Adds NewtonCollisionCfg; contact_gap docstring has a contradictory range claim vs. the sentinel -inf value described
source/isaaclab/isaaclab/sim/spawners/from_files/from_files.py	Adds transition shim routing fragment lists to apply_collision_properties and legacy cfgs to modify_collision_properties; backward-compatible
source/isaaclab/test/sim/test_collision_fragments.py	New test file covering metadata defaults, per-backend namespace writes, multi-namespace composition, and spawner routing

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[collision_props slot] --> B{isinstance list/tuple?}
    B -- yes --> C[coll_frags = collision_props]
    B -- no --> D[coll_frags = wrapped in list]
    C --> E{all SchemaFragment?}
    D --> E
    E -- yes --> F[apply_collision_properties]
    E -- no --> G[legacy define_/modify_collision_properties]
    F --> H[Apply UsdPhysics.CollisionAPI anchor]
    H --> I[For each fragment: call cfg.func]
    I --> J1[apply_namespaced → UsdPhysicsCollisionCfg\nphysics:collisionEnabled]
    I --> J2[apply_namespaced → PhysxCollisionCfg\nphysxCollision:contactOffset etc.\nApply PhysxCollisionAPI]
    I --> J3[apply_namespaced → NewtonCollisionCfg\nnewton:contactMargin etc.\nApply NewtonCollisionAPI]

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flowchart TD
    A[collision_props slot] --> B{isinstance list/tuple?}
    B -- yes --> C[coll_frags = collision_props]
    B -- no --> D[coll_frags = wrapped in list]
    C --> E{all SchemaFragment?}
    D --> E
    E -- yes --> F[apply_collision_properties]
    E -- no --> G[legacy define_/modify_collision_properties]
    F --> H[Apply UsdPhysics.CollisionAPI anchor]
    H --> I[For each fragment: call cfg.func]
    I --> J1[apply_namespaced → UsdPhysicsCollisionCfg\nphysics:collisionEnabled]
    I --> J2[apply_namespaced → PhysxCollisionCfg\nphysxCollision:contactOffset etc.\nApply PhysxCollisionAPI]
    I --> J3[apply_namespaced → NewtonCollisionCfg\nnewton:contactMargin etc.\nApply NewtonCollisionAPI]

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_{Reviews (2): Last reviewed commit: "fix(schemas): type apply_collision_prope..." | Re-trigger Greptile}

[greptile-apps]

The fragments parameter is untyped, unlike the parallel apply_rigid_body_properties which uses Iterable[schemas_cfg.RigidBodyFragment]. Add the matching type annotation for consistency and to let type checkers catch misuse early.

Suggested change

	def apply_collision_properties(prim_path: str, fragments, stage: Usd.Stage | None = None) -> bool:
	def apply_collision_properties(
	prim_path: str, fragments: Iterable[schemas_cfg.CollisionFragment], stage: Usd.Stage | None = None
	) -> bool:

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!