Documentation Is a Compatibility Surface

Documentation does not merely describe the system after the fact. It shapes what operators run, what agents assume, and what reviewers believe has been proven.

When implementation changes, update the operating contract: prerequisites, commands, authority boundaries, expected outputs, and known non-goals. Mark historical or aspirational material so it cannot masquerade as current truth.

The best documentation check is a fresh-checkout exercise. If a new operator cannot reproduce the supported path from the written instructions, the compatibility surface is already broken.