Fix Pytree Metadata resolution and refactor V0 Layout logic

PiperOrigin-RevId: 869831730

Author: angel-core

checkpoint/CHANGELOG.md

@@ -24,6 +24,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - #v1 Make most V1 public concrete classes final.
 - Refactor `CheckpointLayout` splitting `load()` into `load_pytree()` and
 `load_checkpointables()` each with their own dedicated loading logic
+- Refactor v0 Pytree validation and metadata resolution and add `OrbaxV0Layout`
+tests
 
 ## [0.11.32] - 2026-01-20
 

checkpoint/orbax/checkpoint/experimental/v1/__init__.py

@@ -37,7 +37,7 @@
 from orbax.checkpoint.experimental.v1._src.context.context import (
     Context,
 )
-from orbax.checkpoint.experimental.v1._src.layout.orbax_layout import (
+from orbax.checkpoint.experimental.v1._src.layout.registry import (
     is_orbax_checkpoint,
 )
 from orbax.checkpoint.experimental.v1._src.loading.loading import (

checkpoint/orbax/checkpoint/experimental/v1/_src/handlers/composite_handler.py

@@ -291,6 +291,11 @@ def _get_saved_handler_typestrs(
         directory,
     )
 
+    # TODO(b/475265289): Currently, we rely solely on CHECKPOINT_METADATA to
+    # find available checkpointables, ignoring valid subdirectories. We
+    # should update the composite handler to validate subdirectories to
+    # check if any either represents a valid pytree checkpointable or has a
+    # name that is registered in the handler registry.
     saved_handler_typestrs: dict[str, str] = {}
     for checkpointable_path in directory.iterdir():
       if not checkpointable_path.is_dir():