In Jenkins versions > 1.532, MansionComputers are terminated immediately after coming online, before they can be assigned buildable items from the queue.

This happens if the computer takes longer to connect than MansionRetentionStrategy#TIMEOUT

The root cause is hudson.model.Executor#getIdleStartMilliseconds() uses Computer#getConnectTime() to determine idleness if no jobs have been run. However, Computer#connectTime is set when the computer starts connecting.

The solution is to track onlineTime for a MansionComputer and to use that when calculating idleness.