macos: background-opacity getter

macos/Sources/Features/Primary Window/PrimaryWindow.swift

@@ -16,6 +16,14 @@ class FocusedSurfaceWrapper {
 class PrimaryWindow: NSWindow {
     var focusedSurfaceWrapper: FocusedSurfaceWrapper = FocusedSurfaceWrapper()
     
+    override var canBecomeKey: Bool {
+        return true
+    }
+
+    override var canBecomeMain: Bool {
+        return true
+    }
+
     static func create(ghostty: Ghostty.AppState, appDelegate: AppDelegate, baseConfig: ghostty_surface_config_s? = nil) -> PrimaryWindow {
         let window = PrimaryWindow(
             contentRect: NSRect(x: 0, y: 0, width: 800, height: 600),
@@ -53,12 +61,4 @@ class PrimaryWindow: NSWindow {
         
         return mask
     }
-    
-    override var canBecomeKey: Bool {
-        return true
-    }
-
-    override var canBecomeMain: Bool {
-        return true
-    }
 }

macos/Sources/Ghostty/AppState.swift

@@ -82,6 +82,15 @@ extension Ghostty {
             return String(cString: ptr)
         }
         
+        /// The background opacity.
+        var backgroundOpacity: Double {
+            guard let config = self.config else { return 1 }
+            var v: Double = 1
+            let key = "background-opacity"
+            _ = ghostty_config_get(config, &v, key, UInt(key.count))
+            return v;
+        }
+        
         init() {
             // Initialize ghostty global state. This happens once per process.
             guard ghostty_init() == GHOSTTY_SUCCESS else {