Accept pathlib.Path in checkpoint I/O helpers

[ethantsliu]

Accept pathlib.Path in checkpoint I/O helpers

Checkpoint I/O helpers fail on pathlib.Path inputs because cloud-path detection expects a string. Directory downloads also pass local Path destinations into fsspec code that expects strings.

Accept str | os.PathLike[str] for local paths and normalize them with os.fspath(). Directory context managers still yield strings, and cloud URIs are still supplied as strings.

The focused filesystem tests pass (4 tests, including 2 new regression tests). Both new tests fail against the original implementation. Cloud downloads are tested with an in-memory filesystem.

Part of #252.

---

Note

Low Risk
Behavior-preserving type widening and string normalization for local paths; cloud URI handling is unchanged aside from safer local-path coercion.

Overview
Checkpoint and filesystem helpers in io.py now accept str | os.PathLike[str] for local paths instead of strings only. Each entry point normalizes inputs with os.fspath() so cloud URI detection no longer breaks on pathlib.Path, and fsspec/local os.makedirs always receive string paths. Cloud source/destination URIs stay typed as str.

Context managers such as local_work_dir, local_read_dir, and local_read_files still yield strings after normalization. Coverage adds regressions for Path with local work/read flows and for download_directory into a Path destination using an in-memory fsspec filesystem.

^{Reviewed by Cursor Bugbot for commit 8aff1ab. Bugbot is set up for automated code reviews on this repo. Configure here.}

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge with no actionable defects identified.

PathLike values are normalized before string-specific operations, existing string behavior remains intact, and the new tests exercise the intended local and directory-download paths.

Important Files Changed

Filename	Overview
skyrl/backends/skyrl_train/utils/io/io.py	Consistently normalizes PathLike inputs before existing string and fsspec operations without changing behavior for current string callers.
tests/backends/skyrl_train/utils/test_local_read_files.py	Adds focused regression tests covering Path inputs for local context managers and directory download destinations.

_{Reviews (1): Last reviewed commit: "Accept pathlib.Path in checkpoint I/O he..." | Re-trigger Greptile}

[gemini-code-assist]

Code Review

This pull request updates the file I/O utilities in skyrl/backends/skyrl_train/utils/io/io.py to support both str and os.PathLike[str] (such as pathlib.Path objects) for local filesystem paths. This is achieved by updating the type annotations and using os.fspath() to normalize the path arguments before processing. Additionally, corresponding unit tests have been added to verify this new behavior. There are no review comments, and I have no additional feedback to provide.