Function launch_agent_plist 

pub fn launch_agent_plist(exe: &Path, channel: &str) -> String

macOS LaunchAgent plist.

RunAtLoad starts it at login. KeepAlive is deliberately false: the launcher already supervises srv/host and owns its own restart policy, so letting launchd also restart it would give two supervisors fighting over the same process — and would make a user-requested Quit from the tray come straight back, which is worse than useless.