Function is_app_class 

pub fn is_app_class(class_name: &str) -> bool

Phase B.9.1 — does this Win32 window class look like an AgentMux top-level window?

CEF’s top-level windows in CEF 146 use the Chrome_WidgetWin_* class family (CEF Views wraps each native window in a Chromium widget host). AgentMux’s main window shows up as Chrome_WidgetWin_1. Browser-pane child HWNDs and CEF subprocess HWNDs use Chrome_RenderWidgetHostHWND and related — those are explicitly excluded.