Legacy Behavior Ledger#

This ledger is a per-behavior map for the current release. It is not a commitment to copy legacy resolver behavior. It is a map of which legacy behaviors are covered, deferred, or intentionally out of scope for this resolver.

Coverage labels used in the table below:

supported: the 0.1 behavior is implemented and covered by tests.
supported subset: the exact 0.1 subset is implemented and covered; this does not assert complete parity with every legacy resolver behavior.
deferred: intentionally later than the first release unless product priorities change.
out-of-scope: intentionally not owned by this resolver.

Legacy behavior	Coverage	Current owner	Notes
Identifier creation for existing assets	supported	`identifier` module	Covers local/remote distinction, relative remote joins, SDF format args, package identifiers, nested package identifiers, invalid package syntax, and S3 HTTPS host normalization.
Identifier creation for new assets	supported	OpenUSD resolver skeleton	`_CreateIdentifierForNewAsset` uses the same remote identifier normalization path as `_CreateIdentifier`. Write behavior ships in 0.1 for routes whose configured ovstorage backend advertises write support; see “Writable asset open” below.
Default context creation	supported	OpenUSD resolver skeleton, `ScopedDefaultContext`	`_CreateDefaultContext`, `_CreateDefaultContextForAsset`, and `_CreateContextFromString` all return an `OpenUsdResolverContext` wrapping the host-registered default runtime (`setDefaultResolverRuntime`) or an empty context when nothing is registered. The URI-resolver posture means `UsdStage`’s own dispatch of `_CreateDefaultContextForAsset` may not reach a URI resolver’s override in every OpenUSD version, so the portable pattern is to combine process registration with a `ScopedDefaultContext` on each thread that performs OpenUSD work. Covered by `default_context` smoke.
Context creation from strings	supported	OpenUSD resolver skeleton	`_CreateContextFromString` wraps the registered default runtime; the string is preserved as the debug-name suffix and has no configuration semantics. Covered by `default_context` smoke.
Context creation from assets	supported	OpenUSD resolver skeleton, `ScopedDefaultContext`	See “Default context creation” — same override family. Reliable dispatch for URI resolvers goes through `ScopedDefaultContext` (bound via `ArResolverContextBinder`) rather than relying on `UsdStage`’s automatic per-asset dispatch to URI-resolver overrides.
Context binding and unbinding	supported	`ScopedDefaultContext` RAII helper	`ScopedDefaultContext` wraps OpenUSD’s thread-local `ArResolverContextBinder`, giving the constructing thread one binding for the lexical scope without requiring the `Open(url, context)` overload. `setDefaultResolverRuntime` registers the process-wide runtime choice but does not bind worker threads. Covered by `default_context` smoke.
Context-dependent path checks	deferred	Resolver	Not required by the accepted explicit-remote-root and context-bound runtime contract.
Cache scopes (`ArResolverScopedCache`)	deferred	Resolver	The resolver holds no materialized-byte cache and does not integrate with OpenUSD scoped caches. The opt-in Resolve-existence cache is bounded metadata owned by each `ResolverRuntime`, not process-global or `ArResolverScopedCache` state.
Resolve for existing asset	supported	OpenUSD resolver, `ResolverRuntime` existence cache	Scheme-only resolution remains the generic default. With `ResolverOptions::resolveVerifiesExistence`, a context-bound provider stat returns the normalized path for success, empty for authoritative `NotFound`, and the path for all other errors. Positive/negative TTLs, bounded LRU eviction, concurrent coalescing, successful-write invalidation, package/SDF outer keys, generic missing asset composition, no-context behavior, and two-runtime isolation are covered. Legacy-replacement hosts enable the option when `Resolve()` must prove existence. A UDIM tile-set pattern resolves to itself without a stat, whether or not any tile exists, as legacy URI resolvers return it; concrete tiles keep the check (D-0010, #268).
Resolve for new asset	supported	`OvStorageUsdResolver::_ResolveForNewAsset`	Claims the build-advertised URI schemes (`OVS_USD_RESOLVER_URI_SCHEMES`; shipping default `s3;http;https;hf`) for identifier normalization. Writability is checked separately in `_CanWriteAssetToPath` against the bridge’s advertised capabilities. Local paths delegate to OpenUSD’s default resolver.
Extension lookup	supported	`identifier` module, OpenUSD resolver	Covers remote paths, SDF format args, anonymous layer names, package outer extensions for direct resolver calls, and OpenUSD package dispatch through the selected flavor.
Modification timestamps	supported	ovstorage bridge (`stat` mtime), `OvStorageUsdResolver::_GetModificationTimestamp`	The resolver strips SDF format args and package inner path, calls `ResolverRuntime::stat`, and returns `ArTimestamp(mtimeUnixNanos / 1e9)` when the backend reports one (S3 `LastModified`, HTTP `Last-Modified`, file `mtime`, …). Returns an invalid `ArTimestamp` when no mtime is available — mirroring OpenUSD’s “no timestamp” convention.
Asset info	supported	ovstorage bridge (`stat` size/etag/version), `OvStorageUsdResolver::_GetAssetInfo`	`ArAssetInfo::version` takes the ovstorage `version` when present, falling back to `etag`. `resolverInfo` is a `VtDictionary` with `url` (the resolved remote URL), `size` (backend-reported byte count), and `etag` when available. Callers get the resolved-remote metadata OpenUSD/USD tooling expects without inventing semantics ovstorage didn’t provide.
Asset open/read	supported subset	Runtime, storage bridge, bridge-owned `LocalLeaseHandle`	`_OpenAsset` holds a `MaterializedAsset` lease over the bridge-supplied local path. Concrete coverage includes real `file://`, loopback `http://`, native AWS `s3://`, and pinned native `hf://` composition. Other S3-compatible profiles are inherited from ovstorage and not resolver-qualified in 0.1.
`Read` on opened assets	supported subset	Materialized OpenUSD asset wrapper	Covered through `ArFilesystemAsset` delegation after materialization. Direct bridge range reads pass offset and length through ovstorage; the OpenUSD-facing wrapper reads its materialized object through `ArFilesystemAsset`.
`GetBuffer` on opened assets	supported subset	Materialized OpenUSD asset wrapper	Delegated to `ArFilesystemAsset` for the 0.1 USD and USDZ coverage set.
`GetFileUnsafe` on opened assets	supported subset	Bridge-supplied `LocalLeaseHandle` inside `MaterializedAsset`	Delegated to `ArFilesystemAsset` while the bridge lease keeps the path alive for the caller’s use.
Writable asset open	supported	`OvStorageUsdResolver::_OpenAssetForWrite`, `OvstorageWritableAsset`	Temp-file staging via `TfSafeOutputFile` (Replace or Update mode). `Close()` PUTs the normalized whole-object target through `ResolverRuntime::write`; SDF format arguments are removed and package-member targets are rejected. The resolver holds no byte cache; the next `materialize` re-enters the bridge, while a successful write invalidates the affected Resolve-existence metadata key. ovstorage owns materialized bytes and read-your-writes coordination. All three preconditions are wired: LWW overwrite, create-only, and ETag match where the route advertises support.
Materialization	supported	`MaterializedAsset` lease over bridge-supplied `LocalLeaseHandle`	Concrete ovstorage bridge routes to `LayerHandle::read_local_file` when the Layer supports it (the ovstorage runtime owns the local file, GCs on `LocalDelegate` drop); it falls back to a bridge-owned `TempFileLease` for backends such as the shipped HTTP plugin whose Layer surface reports `Unsupported`. The resolver holds no on-disk cache: no `maxCacheBytes`, no LRU, no `release()` verb.
Native bridge materialization	supported	`StorageBridge` contract, concrete ovstorage bridge	Interface, lease handling, and concrete ovstorage bridge materialization smokes exist for `file://` and loopback `http://`. Native `s3://` plumbing ships; live AWS S3 materialization is gated by `OVS_USD_RESOLVER_LIVE_S3_STAGE_URL`.
Identifier-resolution caching	deferred	Resolver	Separate from materialization caching. Any implementation must account for ovstorage permalink/version semantics.
MDL module names	supported subset	`identifier` tests	Built-in-style MDL names are not mistaken for remote storage identifiers.
Remote MDL paths	supported subset	`identifier` tests	Identifier handling is covered. Renderer-side MDL byte IO is outside this resolver.
Package identifiers	supported for reads	`identifier` module, OpenUSD USDZ smoke	Covers identifier parsing/joining plus resolver-level package dispatch for a generated remote USDZ package. Package-member writes are rejected because the storage bridge writes whole provider objects; callers may replace the outer USDZ by naming it directly.
USDZ outer package materialization	supported	OpenUSD USDZ smoke (fake and concrete bridges), bridge-owned `LocalLeaseHandle`	A generated remote USDZ package materializes through the fake bridge (`usdz_package`) and through the concrete ovstorage HTTP bridge over the loopback fixture (`openusd_ovstorage_bridge_usdz`) — the outer package goes through `libovstorage_plugin_http.so` and the resolver holds a bridge-supplied `MaterializedAsset` lease over it while OpenUSD’s package resolver composes it. The composed-stage smoke asserts that SDF format arguments round-trip through `CreateIdentifier`, `Resolve`, and `OpenAsset` on absolute package inner paths, and that no lease files remain in the process’s temp directory after the runtime is released (proves the bridge’s `TempFileLease` destructor unlinks its file on drop). `_OpenAsset` strips both the SDF args and the package inner path before calling into ovstorage so the provider only sees the outer asset URL.
Package-relative and cross-scheme assets	supported	OpenUSD USDZ smokes	Generated USDZ coverage includes an inner layer, composed stage load through `UsdStage::Open(path, context)`, a non-layer internal asset, and a missing inner asset. The deterministic `cross_scheme_usdz` smoke also proves that an absolute layer reference authored inside a package leaves the package context and resolves through a second advertised scheme on the same runtime.
Local file fallback	supported	URI resolver registration	The resolver registration/local fallback smoke proves local files still resolve and open through OpenUSD default filesystem behavior without an ovstorage context.
`file://` ownership	out-of-scope	OpenUSD default resolver	`file` is rejected as a remote scheme. Native local filesystem paths remain owned by OpenUSD’s default resolver and are covered by the local fallback smoke.
`http://` / `https://` ownership	supported subset	Plugin metadata	Plugin registers `http` and `https`, and global `ArGetResolver()` dispatch is covered with an ovstorage context. Supported deployments have one owner for each scheme; duplicate ownership has no supported precedence contract.
Native `s3://` ownership	supported subset	Bridge + plugin metadata	Bridge adopts an `s3`-carrying `LayerHandle`, loaded programmatically or through StackConfig. AWS S3 read/composition is the 0.1 qualified target; non-AWS compatibility profiles require separate qualification.
`omni://` / `omniverse://` ownership	configurable, outside the default scheme list	Host registration and provider routing	A host may advertise these schemes with matching ovstorage routes and a single resolver owner. The default leaves them unclaimed by this resolver; another installed resolver may own them. See coexistence.
ArResolver 1.0 support	out-of-scope	Compatibility posture	First target is OpenUSD resolver behavior for `25.11.kit.4-gl.21081`; legacy resolver remains the reference for older ArResolver support.
ArResolver 2.0 support	supported subset	OpenUSD plugin	The implemented resolver operations build, register, and pass the 0.1 workflow suite against the selected Kit OpenUSD flavor. This is not a claim of exhaustive conformance to every optional resolver behavior.
Search paths and bare asset paths	supported	Identifier module	Bare root assets remain local/default-owned; explicit remote roots anchor relative remote dependencies; remote search roots and implicit discovery are deferred.
Diagnostics and tracing	supported	`ResolverTraceSink`, CLI	Trace sink events cover resolution, Resolve-existence cache hit/miss/wait/coalescing/invalidation, stat, materialization, metadata, and writes. CLI `doctor`, `resolve`, `materialize`, `trace`, `put`, and `benchmark` all ship; `doctor` includes an OpenUSD plugin discovery check and `trace` drives a full `UsdStage::Open` when the CLI is built with the OpenUSD plugin.
Provider request IDs / elapsed-time diagnostics	deferred	ovstorage bridge plus diagnostics	Not part of the 0.1 diagnostic contract.
Python bindings	deferred	Optional tooling	First release does not require Python; helper tooling may follow after C++ ABI stabilization.
Nucleus checkpoints/versioning	out-of-scope	Not owned	Out of scope for this resolver.
Live edit and subscriptions	out-of-scope	Not owned	Out of scope for this resolver.
Hidden omniclient fallback	out-of-scope	All resolver code	This resolver must not link, load, or silently delegate to omniclient.