The validation of configuration keys

As a *configuration file author*, I want to have a means to know what configuration keys will be recognized, so that I can avoid errors arising from key name mistakes.

No files, tests, or entry points are named in the issue. First clarify whether the desired outcome is documentation, an API, validation tooling, or another mechanism for discovering recognized keys, then define acceptance criteria for what configuration authors should be able to inspect and how completion will be verified.

Written by the indexing model from the issue text.