uv add/uv sync/... do not respect the active virtualenv, should they? #6612
Description
Related to #1495, #5229, but not exactly the same IMO.
Like #1495, I prefer to have my virtualenvs located centrally instead of in project directories. I have a Fish shell function called v <NAME> that activates a virtualenv ~/envs/<NAME> if available and cds to the related project directory ~/build/<NAME> if available.
I wanted to try out uv add and uv sync and was initially somewhat confused when they didn't seem to do anything, only to realize that they currently always work on the ~/.venv virtualenv, and don't even stop to consider a currently active virtualenv to work on.
There's apparently a workaround to symlink .venv to the centrally-located venv, but that also seems a bit messy too.
I think it should be at least an (envvar or config-file) option to have the "project venv" tools (run, add, remove, sync, etc.) consider the currently active virtualenv, if any.
Pretty minimal Docker container repro:
~ $ docker run -it python:3.12 bash
root@7ab1d7a6054d:/# pip install uv
Successfully installed uv-0.3.3
root@7ab1d7a6054d:/# mkdir ~/envs
root@7ab1d7a6054d:/# uv venv ~/envs/myenv
Using Python 3.12.4 interpreter at: usr/local/bin/python3
Creating virtualenv at: root/envs/myenv
root@7ab1d7a6054d:/# source ~/envs/myenv/bin/activate
(myenv) root@7ab1d7a6054d:/# echo $VIRTUAL_ENV
/root/envs/myenv
(myenv) root@7ab1d7a6054d:/# mkdir -p ~/projects/myproject
(myenv) root@7ab1d7a6054d:/# cd ~/projects/myproject
(myenv) root@7ab1d7a6054d:~/projects/myproject# uv init
Initialized project `myproject`
(myenv) root@7ab1d7a6054d:~/projects/myproject# uv add ruff
Using Python 3.12.4 interpreter at: /usr/local/bin/python3
Creating virtualenv at: .venv
Resolved 2 packages in 275ms
Built myproject @ file:///root/projects/myproject
Prepared 2 packages in 983ms
Installed 2 packages in 1ms
+ myproject==0.1.0 (from file:///root/projects/myproject)
+ ruff==0.6.2
(myenv) root@7ab1d7a6054d:~/projects/myproject#
(myenv) root@7ab1d7a6054d:~/projects/myproject# uv pip list
(myenv) root@7ab1d7a6054d:~/projects/myproject#