TestPyPI and PyPI: metadata validation parity across the integration boundary

The integration boundary between TestPyPI and PyPI functions as a documented feature for testing package publishing workflows without production credentials. A precise goal is to evaluate whether TestPyPI's API surface and metadata handling replicate PyPI's production constraints, particularly for package uploads, classifier acceptance, and dependency resolution. Uncertainty arises from the lack of explicit parity documentation between the two instances, which may affect the reliability of integration tests as predictors of production deployment success. Does TestPyPI enforce identical metadata validation rules to PyPI for package uploads? Are dependency resolution outcomes consistent across the two instances? Can a package promoted from TestPyPI to PyPI retain its original metadata without re-upload?