When resuming a Job I'd expect the <JOB_NAME>_BUILD_NUMBER and other environment variables to be set to the values from the job being resumed (for subjobs that are not executed during resume)

Without this one is forced to add special logic for sake of resuming build.
It's bad because it clutters the config, and detecting the resume, retrieving the upstream cause and reading envs from it, while doable is not trivial.