Function install_native_toolbar 

pub fn install_native_toolbar(
    id: impl Into<SharedString>,
    title: impl Into<SharedString>,
    items: Vec<NativeToolbarItem>,
    window: &mut Window,
    cx: &mut App,
    on_command: impl Fn(SharedString, &mut Window, &mut App) + 'static,
) -> Result<NativeToolbarHandle>

Install an actual unified AppKit toolbar on the existing GPUI NSWindow.

Use native_toolbar_inset to reserve any native toolbar overlap in a full-size content window. Avoid drawing a second GPUI title/toolbar row. Command callbacks run on GPUI’s foreground executor after the native event, so they cannot reenter an App borrow. The NSWindow delegate stays with GPUI. Use a transparent GPUI window background rather than its separate Blurred backdrop. The bridge supplies AppKit’s semantic window/titlebar background.