[Bug Report] Bug title

[charleskhazoom-aptk]

Title: [bug] Newton USD import drops mjc:frictionloss.

Describe the bug

On the Newton backend, joint Coulomb friction authored on a USD as mjc:frictionloss never reaches the solver — Model.joint_friction / dof_frictionloss stay 0 even though mjc:damping works. Loading a mjcf directly loads everything properly.

Steps to reproduce

Newton core handles it correctly with the mjc resolver, which pinpoints the gap. Minimal (pure Newton):

revolute joint authored with mjc:frictionloss=0.11 on a USD stage

b = newton.ModelBuilder()
solvers.SolverMuJoCo.register_custom_attributes(b)
b.add_usd(stage, schema_resolvers=[SchemaResolverNewton(), SchemaResolverPhysx()]) # Isaac Lab's list
print(b.finalize().joint_friction) # -> [... 0.0] (dropped)

b2 = newton.ModelBuilder(); solvers.SolverMuJoCo.register_custom_attributes(b2)
b2.add_usd(stage, schema_resolvers=[SchemaResolverNewton(), SchemaResolverPhysx(), SchemaResolverMjc()])
print(b2.finalize().joint_friction) # -> [... 0.11] (correct)
End-to-end: any Newton USD robot with mjc:frictionloss authored → dof_frictionloss == 0 in sim.

System Info

• Commit: f703bea7e
• Isaac Sim Version: 6.0.0-rc.22 (release.33481) · Newton 1.0.0
• OS: Ubuntu 22.04
• GPU: RTX 3090
• CUDA: 13.2 (Warp toolkit 12.9)
• GPU Driver: 595.84

Checklist

• I have checked that there is no similar issue in the repo (required)
• I have checked that the issue is not in running Isaac Sim itself and is related to the repo

Acceptance Criteria

• A USD joint with mjc:frictionloss authored yields matching Model.joint_frice Newton backend