deep copy atomic lists sent from one scene to another

HISTORY.md

@@ -49,6 +49,7 @@
 * blocks: only show "key" upvar in the "When ... is pressed" hat if "any key" is selected
 * blocks: tweaked blocks layout for hidden expansion slots
 * blocks, objects, store, threads: made SEND blocks expandable for receivers and renamed them back to BROADCAST 
+* threads: deep copy atomic lists sent from one scene to another
 
 ### 2021-10-21
 * threads, objects: make "when I receive 'any message'" hat scripts threadsafe (uninterruptable by other messages)

src/threads.js

@@ -4683,12 +4683,16 @@ Process.prototype.doSwitchToScene = function (id, transmission) {
         ide, scenes, num, scene;
     this.assertAlive(rcvr);
     this.assertType(message, ['text', 'number', 'Boolean', 'list']);
-    if (message instanceof List && !message.canBeJSON()) {
+    if (message instanceof List) {
         // make sure only atomic leafs are inside the list
         // don't actually encode the list as json, though
-        throw new Error(localize(
-            'cannot send media,\nsprites or procedures\nto another scene'
-        ));
+        if (message.canBeJSON()) {
+            message = message.deepMap(leaf => leaf); // deep copy the list
+        } else {
+            throw new Error(localize(
+                'cannot send media,\nsprites or procedures\nto another scene'
+            ));
+        }
     }
     if (this.readyToTerminate) {
         // let the user press "stop" or "esc",