Thanks for the PR. The path traversal fix is solid, that string-prefix check is a known footgun and this is the right approach.

A few things before merge:

Drop the args.ts change. It guards process with optional chaining on line 8 (nodeProcess?.env?.DEBUG) but not on line 30 (nodeProcess.platform), so it crashes if process is actually undefined. And only args.ts gets this treatment while 5 other files in js/src/ use process directly. This is incomplete and introduces a bug. Please revert and handle it in a separate PR if there's a use case.

Use the built-in instead of the helper. Python 3.9+ has Path.is_relative_to() and we require >=3.9. The _path_is_relative_to() function can be replaced with:

if not member_path.is_relative_to(dest_resolved):

Merge doctor into info. The only new things doctor adds over info are Python version, OS, and module availability. That doesn't justify a separate command. Could you add those fields to info instead?

Fix the test mock. test_doctor_prints_environment_without_downloading mocks ensure_binary, but the function calls binary_info(), which never triggers a download. The mock is a no-op. Either remove it or mock something the function actually calls.

Minor:

• Remove # type: ignore[import-not-found] on the pytest import in test_extract.py. No other test file has this.

The extraction fix and its tests are good. The Windows _is_executable improvement and platform-neutral test assertions are welcome too. Just needs these cleanups.

Let me know if you have questions on any of these.