Automate the package build/distribution check across PyPI repos #568

Summary

Packaging correctness of the wheel and sdist is verified via agentic prompting per PR today. We should turn it into one reusable, automated check adopted across all PyPI-publishing repos.

The packaging check on DoneXBlock#388 is a real run of it — it caught the test package shipped into the wheel, NOTICE dropped, and the sdist bloated with coverage artifacts.

Proposed work

Build a reusable check (e.g. a shared GitHub Actions workflow) that builds the wheel + sdist and asserts:

• Test packages and .pyc files are not shipped into the wheel.
• Required files are present — sources, static assets, LICENSE, NOTICE, METADATA/PKG-INFO.
• The sdist is pruned — no htmlcov/, coverage.xml, or .coverage.
• No content regressions versus the base branch in the wheel or sdist.

Acceptance criteria

• Reusable packaging check created.
• Adopted across the PyPI-publishing repos.

Implementation approach

Reusable GitHub Actions workflow (recommended) — a workflow_call workflow in a central repo composing check-manifest, check-wheel-contents, and twine check, plus a step asserting LICENSE/NOTICE.
Repos adopt it with a small caller job, so central fixes propagate everywhere without per-repo changes.

Shared tox target / test module — the same checks packaged as a tiny installable each repo runs in its own test suite.
Gives local control, but every update needs a PR per repo, so it is weaker for org-wide rollout.