Register HEAD explicitly

A GET route doesn't automatically handle HEAD or OPTIONS. Register HEAD when you want clients to fetch the headers without the body.

export function plainApp(service: GreetingService) {
  const app = createApp();
  app.router.get("/readers/:id", (req, res) => {
    res.json({ message: service.message(toHttpId(req.param("id"))) });
  });
  app.router.head("/readers/:id", (req, res) => {
    toHttpId(req.param("id"));
    res.header("content-type", "application/json; charset=utf-8").send("");
  });
  return app;
}

The plain route uses router.head; the controller uses @Head. Both apply the same parameter validation and content type as GET while sending an empty body. Keep authorization, existence checks, cache headers, and other representation headers equivalent in your real routes. HEAD should not perform a write. If you send Content-Length, describe the GET representation, not the empty HEAD body.

The first-route test deliberately expects HEAD to return 404; the explicit routes expect 200 and an empty body. staticAssets is a separate web helper that does handle GET and HEAD for its own exact asset map. That behavior does not alias application routes.