fix: llama stack build use UV_SYSTEM_PYTHON to install dependencies to system environment

[yanxi0830]

What does this PR do?

• resolves issue: Colab notebook broken with dependencies missing #1159
• Root cause: fix: improve stack build on venv #980 forces build_venv.sh to install in a venv environment, which do not work on Colab notebook environment

This PR

Use UV_SYSTEM_PYTHON to make sure dependencies are installed in current system environment. Which will be used in the Colab environment.

UV_SYSTEM_PYTHON=1 llama stack build --template together --image-type venv

Test Plan

• Works in Colab environment

[SLR722]

Thanks for the quick fix!

[ashwinb]

Hm, I wonder if we really need this additional complexity again. A proposal: if we just base our operation on the UV_SYSTEM_PYTHON env variable? If that is set, we know we don't intend to create a separate venv -- this is the variable uv has settled upon and we already use it in the notebook example?

[yanxi0830]

Hm, I wonder if we really need this additional complexity again. A proposal: if we just base our operation on the UV_SYSTEM_PYTHON env variable? If that is set, we know we don't intend to create a separate venv -- this is the variable uv has settled upon and we already use it in the notebook example?

ugh my bad, just realized I've been using UV_SYSTEM_PROMPT to test and hence added the flag. updated the script now

[ashwinb]

Also, please update the PR summary also!

[ashwinb]

oh I missed this, but I think you need to initialize this before the set -euo pipefail otherwise you will get a failure if this env var is not set.

[yanxi0830]

I think the ${UV_SYSTEM_PYTHON:-} part will cover it, but just to be consistent: ca687d3