free-threaded wheel not picked in pip dependencies

[lesteve]

Checklist

• I added a descriptive title
• I searched open reports and couldn't find a duplicate

What happened?

To reproduce:

cat << EOF > /tmp/environment.yml
channels:
  - conda-forge
dependencies:
  - python
  - python-freethreading
  - pip
  - pip:
    - numpy
EOF

conda-lock lock -f /tmp/environment.yml -p linux-64
grep numpy-2 conda-lock.yml

Expected behaviour: the numpy free-threaded wheel is picked up i.e. cp313-cp313t (t at the end). There are some free-threaded wheels available for numpy as you can see from PyPI.

Actual behaviour: vanilla Python wheel is picked up i.e. cp313-cp313 (no t at the end).

Output:

  url: https://files.pythonhosted.org/packages/70/50/73f9a5aa0810cdccda9c1d20be3cbe4a4d6ea6bfd6931464a44c95eef731/numpy-2.1.3-cp313-cp313-manylinux_2_17_x86_64.manylinux2014_x86_64.whl

If you try to create the environment from the lock-file:

conda-lock install -n test-ft conda-lock.yml

You will get an error:

ERROR:root:ERROR: numpy-2.1.3-cp313-cp313-manylinux_2_17_x86_64.manylinux2014_x86_64.whl is not a supported wheel on this platform.

Additional Context

This was noticed in a scikit-learn context but this is probably not super high priority, since I suspect the number of people using conda-lock with free-threaded is low.