Golden and snapshot tests

Goldens are the frozen answers of an app: the readable text a pure unit produces for fixed inputs, the output every installed version must reproduce, the pixels a Skia surface draws. They change only on purpose, after a real look, in a commit that says why, and contract entries never change at all. This skill writes them in the Jest golden project and its two checkers prove that the tree and the git history keep that policy.

Rules that must hold