context counter

agent Counter {
  key id: String
  store n: Cell[Int] = 0

  on call bad_op() -> Effect[()] {
    let _ <- n.foo()
    Effect.pure(())
  }
  on call bad_arity() -> Effect[()] {
    let _ <- n.update()
    Effect.pure(())
  }
  on call bad_arg() -> Effect[()] {
    let _ <- n.update((c) => "x")
    Effect.pure(())
  }
}
