Obviously, you could just let the build fail and then the developer can look at those error messages and determine what jar is not available in Nexus But what if you want to preempt that. Say scan the pom and discover it is looking for a jar you don't want in your Nexus instance. Thus allowing you to send a message via that agent to the code owner indicating they need to upgrade, remove, whatever that jar from their project.
I know you can probably add a step to the agents to do this first, but what if you have 1,500 agents running? Is there an easier way to do this without requiring each agent to add it to their pipeline?
