Arc diff -- abort / preview

I haven’t found in the arc documentation how to cancel an arc diff once you run the command. Is that possible or does it always result in publishing something?

I also haven’t found a way to preview (locally) without sending to the review server. I’ve been using arc diff --only, but it pushes to the server. This serves my purpose, but seems unnecessary – I only want to check that I specified the correct git commit hash.

The closest I know of for “preview” is this option:

          Create a draft revision so you can look over your changes before
          involving anyone else. Other users will not be notified about the
          revision until you later use "Request Review" to publish it. You
          can still share the draft by giving someone the link.