In a multiple user context, with concurrent builds enabled, it can be difficult to find the build number. nextBuildNumber isn't always what the build number is going to be (race because of concurrent builds).

It would be nice to have:

http://jenkins.example.com/job/example/build?getBuildNumber that would wait until the build starts running to return the build number.

and

CLI counterpart; that returns when the build number is available.