Usd Layer Stack Open

usd-layer-stack-open

Use this skill when implementing or verifying recursive local sublayer loading from resolved layer resources into a layer-stack namespace source.

Spec Sources

• specification/composition/README.md sublayer and layer-stack inputs
• specification/document_data_model/README.md subLayers and subLayerOffsets
• USD Core Spec Resource Interface sections covering resolved resources, local file resources, URI references, and package resource spelling

Pinned tag / commit: v1.0.1

Provides

• Opening a root layer resource
• Reading subLayers from the opened root layer and recursively opened local sublayers
• Resolving local sublayer identifiers relative to the layer that authored them
• Opening recursively discovered local sublayer resources through usd-layer-open
• Detecting recursive sublayer cycles by resolved layer location
• Construction of a LayerStackNamespaceSource from opened layers
• Layer-stack-open diagnostics for missing, unsupported, failed, or cyclic sublayers

Contract

This skill owns contracts/handles/layer-stack-open.handle.json and bridges the single-layer opener with the in-memory layer-stack namespace source.

This is a bounded recursive local sublayer loader. It accepts a resolved root resource location, opens it with usd-layer-open, reads each opened layer's authored subLayers field, resolves each local sublayer using the prototype policy below, opens recursively discovered sublayers with usd-layer-open, and passes the opened layers to usd-layer-stack-namespace-source.

The output is a target-native result containing either a LayerStackNamespaceSource or diagnostics. It must not be a canonical JSON dump, a parser-local USDA tree, or a separate JSON spec store. JSON appears only in conformance adapters and diagnostic serialization.

Local Resolution Policy

This is not full USD asset resolution. It is a bounded local policy for the first actual-sublayer contract:

• local filesystem layer resources may resolve relative sublayer identifiers against the containing directory of the layer that authored the subLayer
• local file URI roots may resolve relative sublayer identifiers against the containing file URI path of the authoring layer
• explicit local file URI sublayers may be passed through as resolved locations
• unsupported URI schemes fail clearly
• package resource sublayers remain unsupported in this contract
• resolver search paths, resolver callbacks, contexts, layer identifiers, and non-local protocols remain deferred

For this prototype, plain relative asset identifiers such as asset.usda and anchored relative identifiers such as ./asset.usda are both resolved relative to the layer that authored the subLayer. This is a local resolver policy, not a claim of full asset resolution.

Boundary Guards

Consume usd-layer-open to open the root and every recursive sublayer. Do not read files directly and do not invoke USDA parsers from this node.

Consume usd-resource-protocol for resolved-location classification and local resource rules. Do not add ad hoc URI parsing, package splitting, or unsupported scheme fallback to filesystem paths.

Consume usd-layer-stack-namespace-source to construct the composed namespace source from opened layers. Do not duplicate child/property composition, effective specifier rules, or field-strength merging in the loader.

Consume the document-model layer returned by usd-layer-open; do not retain canonical layer dump JSON as source storage.

Do not perform references, payloads, inherits, specializes, variant composition, relocates, schema fallback evaluation, value resolution, stage population, or instancing.

Test Obligations

• root layer resource opens through usd-layer-open
• recursively discovered local sublayers open through usd-layer-open
• opened layers are passed to usd-layer-stack-namespace-source
• stack summary preserves root plus recursive sublayers and subLayerOffsets in depth-first strength order
• composed source queries work after resource loading
• missing sublayer resources fail clearly
• unsupported sublayer URI schemes fail clearly
• recursive sublayer cycles fail clearly and do not recurse unboundedly
• all cases in goldens/unit/usd-layer-stack-open/layer-stack-open.json