Function second_instance_opens_window 

pub fn second_instance_opens_window(args: &[String]) -> bool

A launcher that finds AgentMux already running forwards open_new_window to it, so a double-click opens a window. A login entry firing while the user already has AgentMux open must not (SPEC_START_WITH_OS_2026_09_25.md §3.6): it just exits.