Shaders now are managed by a manger that can do hot reloading and it also will detect a bad shader and use an ERROR shader so you know it's busted visually.

gui_fsm.cpp

@@ -286,6 +286,7 @@ namespace gui {
           case KEY::P:
             sound::mute(false);
             $debug_ui.debug();
+            shaders::reload();
             break;
           case KEY::O:
             autowalking = true;