OpenUSD Composition

Manage layer composition arcs: add sublayers to the root layer, attach payload arcs on prims, create variant sets, and set variant selections. Reference arcs remain in openusd-stage. Requires the pxr OpenUSD runtime.

Workflow

1. Ensure a stage exists.
2. add_sublayer — compose another layer under the root layer.
3. add_payload — attach a payload arc on a prim.
4. add_variant_set — create a named variant set on a prim.
5. set_variant_selection — switch the active variant in a variant set.