When a build is run on a agent the link to agent information is displayed on build console. But for ephemeral agent or agent that has been removed since this link is invalid.

Today, navigating on link to a agent that does not exists anymore display a standard HTTP 404 error page. I would be more user friendly to have instead a message "agent not available anymore" or something similar.

Steps to reproduce (it's more hit by ephemeral agent, but to reproduce it's faster with permanent):

• Create a permanent agent with a label "onlyme"
• create a freestyle job, restrict to run only on "onlyme"
• run job
• delete agent
• go on build console, and click on agent link

See gif in attachement.