Build and publish a Python package with uv (uv build, uv publish, tokens, custom indexes)

Documented steps

1. Ensure pyproject.toml has a `[build-system]` table (projects created with `uv init` include one by default; the docs strongly recommend configuring a build system).
2. Build: `uv build` — builds the project in the current directory and places the sdist and wheel in `dist/`. In a workspace, target a member with `uv build --package <name>`.
3. Publish to PyPI: `uv publish` with a token: `--token <token>` or the UV_PUBLISH_TOKEN env var.
4. Publish to a custom index: define it under `[[tool.uv.index]]` with a `publish-url`, then run `uv publish --index <name>` (UV_PUBLISH_INDEX can hold the name).
5. Smoke-test the published package without your local sources interfering: `uv run --with <package> --no-project -- python -c "import <package>"`.
6. Docs: https://docs.astral.sh/uv/guides/package/