Concurrent builds per agent. Leave at 1 unless builds are light and isolation does not matter — agents are single-use and cheap.

At 1, the instance is destroyed as soon as its build finishes, so the idle timeout below only applies to an agent that connects but is never given work. Above 1, the agent is kept until it has been idle for that timeout, because terminating it after the first build would kill the builds still running on its other executors.