Function list_window_instances 

pub fn list_window_instances(state: &Arc<AppState>) -> Value

List all open window instances with their backend window IDs. Same filtering as list_windows (excludes unpromoted pool windows and browser-pane child HWNDs), but returns [{label, windowId}] pairs so the frontend can resolve per-window backend objects (Window record → meta[“window:displayname”], etc.) without an extra round-trip per row.

windowId is None for windows that haven’t yet completed the register_backend_window round-trip — typically a freshly-spawned window before its frontend has finished init. Callers should fall back to label/index-based naming in that case.