Saving now works over insecure networks.

src/components/Emulator.tsx

@@ -28,7 +28,8 @@ type ReceiveEmulatorMessage = (
   { message: 'ready' } |
   { message: 'save_state' } |
   { message: 'load_state' } |
-  { message: 'save', data:string }
+  { message: 'save', data:string } |
+  { message: 'error', error:string }
 );
 
 export type EmulatorProps = {
@@ -94,6 +95,9 @@ export const Emulator:React.FC<EmulatorProps> = props => {
           save(msg.data).catch(console.error);
           break;
 
+        case 'error':
+          console.error('Emulator error:', msg.error);
+
         case 'start':
         case 'ready':
         case 'load_state':