Typescript force 'atmost once' on type-level

forceOnlyOnce.ts

// use cases: class decorators, etc

function forceOnlyOnce (test: string & {__T?: undefined}) {
  const test2: string = test

  return test2 as string & { __T: null }
}

const a = forceOnlyOnce('123')

// type-error below:
forceOnlyOnce(a)