Prevent invalid state changes

[oreoshake]

The API doesn't like invalid state changes or even state changes to the current state. This can lead to confusing 400 errors.

For the case where you're doing a state change to the current state, we could raise an error in the client.

For the other cases, we'd probably need to map out the valid transitions and check this prior to making a call.

/cc @brentjo @gregose