Refactor Codebase with Types

Surface refactoring opportunities inspired by Alexis King's “Parse, don't validate” and “Types as axioms.” The aim is to move facts learned at runtime into values and types so valid states are easy to construct, invalid states are hard or impossible to represent, and execution code stops re-checking things boundary code already proved.

Glossary

Use these terms exactly in suggestions. Full definitions are in LANGUAGE.md.