In our environment we have a message bus we can monitor and update. During the imaging process messages are delivered that give the status of the build. We also update our machine database with this same build information so we can check either spot for the completion. Both have api's. The message bus is more accurate time wise but either works for us. You could engage with those teams to see if they can make something that is easily queryable and then embed those in the api. Another option is using the guest tools, ssh, powershell, something that logs into the vm with a service account and can examine local logs for something similar.
