pub fn parse_active<S>(&self) -> Result<Option<S::Rx>, ClientError>
    where
        S: MakeRx,
        S::Rx: MakeUnrx<Unrx = S> + AnyFreeze + Clone,
    {
        match &self {
            // If there's an issue deserializing to this type, we'll fall back to the server
            Self::Loaded(any) => {
                let rx = any
                    .as_any()
                    .downcast_ref::<S::Rx>()
                    .ok_or(ClientInvariantError::GlobalStateDowncast)?
                    .clone();
                Ok(Some(rx))
            }
            Self::Server(_) | Self::None => Ok(None),
        }
    }
Parses the global state into the given reactive type if possible. If the
state from the server hasn't been parsed yet, this will return
`None`. This will return an error if a type mismatch occurred.

In other words, this will only return something if the global state has
already been requested and loaded.
packages/perseus/src/state/global_state.rs