Build a small, entirely self-contained project from the empty tree: its layout, its build configuration, and one working thing plus the tests that prove it.

Build a small, entirely self-contained project from the empty tree: its layout, its build configuration, and one working thing plus the tests that prove it. Depend on nothing that must be fetched — no packages, no network at build or test time. The deliverable is a tree that a fresh checkout can build and test with a single command run from the root, with the command and the expected output written down in a short README.

Keep the scope to one component with a narrow, documented interface and a test suite that exercises its edge cases, including the inputs it would rather not be given. Prefer boring and complete over ambitious and half-wired: the point of this job is a green tree in a place that has never held one.