Function isDockerfileRef

packages/container/src/util.ts:86–94

(ref: string)

 * treating the path as a prebuilt image.
 */
export function isDockerfileRef(ref: string): boolean {
  const base = basename(ref).toLowerCase();
  return (
    base === 'dockerfile' ||
    base === 'containerfile' ||
    base === 'dockerfile.vercel' ||
    base === 'containerfile.vercel'
  );
}

// Vercel-specific container opt-in markers, auto-discovered when the build
// entrypoint doesn't name a Dockerfile explicitly (e.g. the `container`