Fix desync between fade out/in and level loading when game is lagging.

modules/game/scripts.scm

@@ -7,6 +7,7 @@
             script?
             run-script
             script-cancel!
+            yield
             wait
             forever
             tween)
@@ -102,9 +103,8 @@
                          (current-scheduler scheduler))
             (thunk)))
         handler)))
-  (define (handler k delay)
-    (when delay
-      (scheduler-add! scheduler (lambda () (run k)) delay)))
+  (define (handler k proc)
+    (proc (lambda () (run k))))
   (when (script-pending? script)
     (let ((parent (current-script)))
       (when parent
@@ -112,20 +112,20 @@
     (run
      (lambda ()
        (set-script-state! script 'running)
-       ((script-cont script))
-       ;; Nasty hack: For some reason, falling through the prompt
-       ;; thunk messes up the Scheme stack, resulting in an invalid
-       ;; ref.cast somewhere.  So, we *never* fall through.  Instead,
-       ;; we create a continuation that gets thrown away.
-       (abort-to-prompt %script-tag #f)))))
+       ((script-cont script))))))
 
 (define (run-script thunk)
   (let ((script (make-script thunk)))
     (script-run! script)
     script))
 
+(define (yield proc)
+  (abort-to-prompt %script-tag proc))
+
 (define (wait delay)
-  (abort-to-prompt %script-tag delay))
+  (yield
+   (lambda (thunk)
+     (scheduler-add! (current-scheduler) thunk delay))))
 
 (define-syntax-rule (forever body ...)
   (let loop ()