I've replaced the linkbait title with an attempt at saying what the feature is. If there's a more accurate wording, we can change it again.
When we talk about local dependencies in the Python packaging ecosystem, it's usually adding some package on your file system to your environment. The existing title made me think this would be about the `[tool.uv.sources]` feature.
Really, it's about how we create environments on-demand and make it trivial to add packages to your environment or try other Python versions without mutating state.