RFE: Improve the "No interpreter found" error message when python-downloads is set to "manual"

[hroncok]

Hello.

Consider /etc/uv/uv.toml with:

python-downloads = "manual"

And a system without Python 3.X installed.

When I attempt to use Python 3.X, I get an error:

$ uv venv --python=python3.X venv
  × No interpreter found for Python 3.X in managed installations or search path

This is expected. I opened this issue to ask if the error could be more verbose (and actionable). The most relevant things that I would love to see there are:

• Not downloading Python 3.X because python-downloads is set to "manual" in /etc/uv/uv.toml.
• Run uv python install 3.X to manually install it.

Thanks for considering this.

Unfortunately, my Rust skills are 0 and I am not familiar with uv codebase at all, so I won't be able to contribute this.

---

• The current uv platform: Fedora Linux
• The current uv version (uv --version): 0.5.4