Comment # 11 on bug 1091818 from Neil Rickert

My understanding, which could be wrong, is that when an application needs to
communicate with gpg-agent, it starts it.  With recent gpg versions, the agent
socket location is at a standard location in the file system, so does not need
to be passed via the environment.  Because of that, it is not necessary to
start the agent at session startup.

This should apply to both Tumbleweed and Leap 15.0.  However, for Leap 42.3, it
still needs to be started as session startup because that's using an older gpg
version.