restricted inter-scene messages to text and numbers

HISTORY.md

@@ -38,6 +38,7 @@
 ### 2021-09-30
 * blocks, objects, threads, gui: optional upvars referencing event data for message, key and scene hat blocks
 * blocks: disabled dropping reporters onto message hat block input slots
+* threads: restricted inter-scene messages to text and numbers
 
 ### 2021-09-29
 * objects, blocks: refactored experimental "When I receive message" hat block

src/threads.js

@@ -4730,6 +4730,7 @@ Process.prototype.doSwitchToScene = function (id, transmission) {
         message = transmission.at(1),
         ide, scenes, num, scene;
     this.assertAlive(rcvr);
+    this.assertType(message, ['text', 'number']);
     if (this.readyToTerminate || this.topBlock.selector === 'receiveOnScene') {
         // let the user press "stop" or "esc",
         // prevent "when this scene starts" hat blocks from directly