fix: resolve HF symlinks in from_hub via temp local_dir

[Disha714]

Fixes #1492.

Summary of Changes

• from_hub downloads via huggingface_hub.snapshot_download with the default cache layout, where io_configs/*/io.yaml entries in the returned snapshot directory are symlinks into a sibling blobs/ directory outside the snapshot root. This violated from_model_directoryx27s documented self-contained-directory contract and tripped the path-escape check.
• Rather than loosening or touching the security check in from_model_directory, this PR updates from_hub to download files into a temporary self-contained local directory via with tempfile.TemporaryDirectory() as local_dir: and passing local_dir=local_dir to snapshot_download. This populates the temporary directory with real files rather than symlinks escaping the directory.
• Passes the return value of snapshot_download (downloaded_dir) to from_model_directory so that both runtime operations and mocked test fixtures operate reliably.

Verification & Security

• Security Barrier Untouched: Verified locally that all security-relevant unit tests (test_path_traversal_in_io_config_raises, test_symlink_escape_in_io_config_raises) pass cleanly, confirming that the directory traversal / path-escape defenses remain 100% intact for any malicious input.
• Regression Testing: Added a dedicated unit test test_from_hub_requests_local_dir to explicitly verify that from_hub passes local_dir to snapshot_download. Updated existing test mocks across TestFromHub and TestFromSource to expect local_dir=ANY.
• Test Suite Results: Executed uv run --extra switch pytest test/backends/test_adapters/test_embedded_adapter.py -v; all 38 tests passed locally without errors or regressions.

[AngeloDanducci]

Hello, thanks for the contribution!

Overall I think this look good. One test question and I will ping @planetf1 for his 2C since he was the original issue author.

May be worth adding another test where from_hub loads adapters when snapshot_download populates local_dir with real files (as huggingface_hub does with local_dir set).

[planetf1]

(superseded — see consolidated review below)

[planetf1]

(superseded — see consolidated review below)

[planetf1]

(superseded — see consolidated review below)

[planetf1]

The symlink-escape fix is correct, but cache_dir is silently defeated:

• Cache always cold: local_dir prevents cache_dir from ever being written to; each call is ~51 HTTP round-trips with zero reuse
• Offline broken: HF_HUB_OFFLINE=1 raises LocalEntryNotFoundError

Suggested fix: Use a persistent directory under cache_dir/HF_HUB_CACHE + repo + revision instead of TemporaryDirectory(). Verified: restores caching (0.9s → 0.1s warm) and offline operation while keeping the self-contained layout.

Inline comments on test gap and docstring nit follow.

[planetf1]

@Disha714 Hi - are you able to update the pr to address the comments & resolve conflicts
Let us know if you have any questions or need to hand over

[planetf1]

As we've not heard, I'll push fixes to the comments above so that we can get this merged - thanks for the pr.

[planetf1]

I've actioned the review fixes & done a further review -- this has been updated in b94cd9e.

This is now rebased on current main. from_hub resolves through the normal Hub cache and materialises only the adapter index and referenced configs into a commit-keyed self-contained directory, keeping the local path guard strict.

Validation:

• 41 adapter tests
• full non-qualitative suite: 4123 passed, 47 skipped, 128 deselected
• ruff, mypy, pre-commit, and Hub 0.33.4 compatibility check

Superseded by the updated implementation and fresh review request.