[BUG][pathfinder] Incorrect site-packages search order for venv created with --system-site-packages #1716

This summarizes a group chat discussion and additionally documents Cursor-based verification:

Problem

When cuda.pathfinder.load_nvidia_dynamic_lib searches for NVIDIA dynamic libraries in site-packages, it currently searches in the following order unconditionally:

1. User site-packages (site.getusersitepackages())
2. Site packages from site.getsitepackages() (which includes both virtual environment and system site-packages)

This ordering causes issues in a venv created with --system-site-packages: according to PEP 405 the correct search order should be (verified as explained below):

1. Virtual environment site-packages
2. User site-packages
3. System site-packages

Cursor-based verification

PEP 405 (Virtual Environments):

• States that in a venv with --system-site-packages, system site directories are added after virtual environment site directories.
• Notes that PEP 370 user-level site-packages are considered part of system site-packages for venv purposes.

PEP 370 (User Site-Packages):

• States that user-site-packages are added before system site-packages (outside venv context).

Actual Python Behavior (verified by test):
In a venv with --system-site-packages, Python's sys.path order is:

1. Virtual environment site-packages
2. User site-packages
3. System site-packages

This confirms that the correct search order described above matches both PEP 405, PEP 370, and Python's actual behavior.

References

• PEP 405: https://peps.python.org/pep-0405/
• PEP 370: https://peps.python.org/pep-0370/