JENKINS-41745: Deprecate the Remoting-based protocol for the Jenkins CLI feature. Enhance the client and server to conveniently perform most existing CLI tasks with simpler and safer protocols.
During development, we sometimes need to figure out whether a behavior is a regression, or just in general to see how Jenkins used to behave in the past. This is complicated by update sites only being generated for the last year of Jenkins releases, and older Jenkinses will fail to install plugins that have too recent minimum requirements. This document explains how to work around that.
Jenkins infrastructure uses mirrors to distribute update site downloads and metadata. These mirrors are not automatically cleaned up, so when the project stops publishing an update site tier (~ downloads for a specific version of Jenkins), those remain available on mirrors.