anchor.diff:          callStackView.showFrames(frames, selectTop: true);
         } else {
           callStackView.clearFrames();
  -        sourceEditor.clearExecutionPoint();
  +        sourceEditor?.clearExecutionPoint();
         }
       }
   
  
positive.code:       sizes: [80, 20],
        minSize: [200, 60],
      );
    }
  
    @override
  
negative.code:     stepIn.click(() => debuggerState.stepIn());
      stepOut.click(() => debuggerState.stepOut());
  
      void updateFrames() async {
        if (debuggerState.isPaused.value) {
          // Check for async causal frames; fall back to using regular sync frames.
  