Find a unique identifier for a Diffusion repository from a Git repository?

I think the only way right now is to get the remote uri, call repository.query with it, and parse that.
It might make sense to just teach arc which to output it's things in json.

The trouble is that that could sometimes give the wrong answer, because querying the Git URI is not the only way that arc itself finds the repository; for example, the repository callsign can be hardcoded into .arcconfig.

As you say, machine-readable output for arc which would be helpful, here.