Caching for managed python installations

[aokellermann]

Summary

The current guidance for caching in docker images is:

ENV UV_LINK_MODE=copy
RUN --mount=type=cache,target=/root/.cache/uv \
    uv sync

The UV_LINK_MODE=COPY is crucial, as the cache is not mounted during container runtime.

However, this only works for package cache, and not for managed python installations. So if my image doesn't have python already installed, uv downloads it and puts it in a non-cached filesystem (/root/.local/share/uv by default). It would be nice if there was some way to have a UV_LINK_MODE analog, but for managed python so that if one mounts a python cache, uv sync will copy python to the image filesystem.

[zanieb]

There's a UV_PYTHON_CACHE_DIR, it's just not on by default.

[aokellermann]

thanks! opened documentation PR for this