[Kayvan-Zahiri]

Relative source paths beginning with - cannot reliably be copied with Sandbox.fs.copy: shell quoting preserves the string, but cp still interprets it as an option. For example, copying -source to copy fails instead of copying an existing file.

Add -- before the two quoted operands in the command shared by sync and async copy. Existing quoting and process completion handling remain intact.

Validation: six public sync/async API regression cases execute the emitted command against temporary local files (four fail before the change, six pass after). Full suite: 449 passed, 86 skipped. Repository lint and type checks, wheel/sdist builds and git diff --check pass. Live Baseten E2E tests were skipped; this reproduces command construction locally through HTTPX mock transport. Developed with AI assistance and verified locally.

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[cretz]

Hi, just noticed this draft PR. Let me know if this is something you are hitting and when it is ready for review.

[Kayvan-Zahiri]

Not in production. I found it while reading the copy code: a source path starting with - gets parsed by cp as an option. It's ready for review now, thanks for taking a look.

[cretz]

To confirm, you are not a Baseten user hitting this issue at this time? Or is this just from a scan and you aren't using this code yourself?

This also exists in other SDKs and in Blaxel at https://github.com/blaxel-ai/sdk-python/blob/e9b63fd6bf8eabd02c451510a733e29615644fbf/src/blaxel/core/sandbox/sync/filesystem.py#L175 and in other places. I want to confirm impact.

[Kayvan-Zahiri]

Right, I'm not a Baseten user and haven't hit this myself. I found it while reading through sandbox SDK code, so it comes from a review, not a bug report. The impact is small: it only affects a relative path that starts with -, since absolute paths always start with /. If that isn't worth a change on your side, I'm fine with closing it.

[cretz]

This is less of a concern at this time. I do think we'll close it and when we tackle, we can do it across all 3 SDKs.

[Copilot]

🟢 Approval recommended

The focused fix preserves existing behavior and has regression coverage for both APIs, with no unresolved findings.

No open issues 🎉

What changed in this PR

Fixes Sandbox.fs.copy so dash-prefixed paths are treated as operands rather than command options in both sync and async APIs.

Changes:

• Adds -- before copy operands while preserving shell quoting.
• Adds six regression cases and updates the existing command assertion.

File	Description
tests/​sandbox/​test_fs.py	Updates the expected copy command.
tests/​sandbox/​test_copy_paths.py	Tests dash-prefixed paths through both APIs.
baseten/​sandbox/​_fs.py	Ends option parsing before copy operands.

_{Review effort: Balanced}