message: add more toward the skeleton state apply
diff: @@ -28,8 +28,11 @@ pub struct State {
  pub(crate) leadership: Leadership,
  }
  +type Error = ();
  +
  impl State {
  - pub fn apply(&self, content: BlockContents) -> State {
  + pub fn apply(&self, contents: BlockContents) -> Result<State, Error> {
  + for content in contents.iter() {}
  unimplemented!()
  }
  }
  