Does Orion support canceling/restarting runs?

Not yet, but a lot of similar functionality is on the roadmap. As of now, you can set a custom flow run state via an API call using Orion client, for example, to set it to a canceled or completed state, and then you can start a new run. But also, since any run even from your terminal is connected to the backend, you can kill the local process and this will cancel the run.