Hard to believe, but I think fullscreen truly works, even through sleep.

desktop/src-common/advent/screens/safe.clj

@@ -8,6 +8,7 @@
             [advent.zone :as zone]
             [advent.utils :as utils])
   (:import [com.badlogic.gdx.graphics Pixmap Pixmap$Filter Texture Texture$TextureFilter]
+           [com.badlogic.gdx.utils.viewport FitViewport]
            [com.badlogic.gdx.graphics.g2d TextureRegion]
            [com.badlogic.gdx.scenes.scene2d.utils Align]
            [com.badlogic.gdx Application Audio Files Game Gdx Graphics Input
@@ -58,7 +59,8 @@
 
   
   :on-render
-  (fn [screen [entities]]
+  (fn [{:keys [^FitViewport viewport] :as screen} [entities]]
+    (.apply viewport)
     (when (:shown? entities)
       (render! screen [(:fade entities) (:safe entities)])
       (render! screen (take (count (:button-choices entities)) (:entered-keys entities))))