Library symbol not recognised

in my fla file i have 1 symbol in the library with the export name: “Box”
my document class:

package {
    
    import flash.display.MovieClip;
    import flash.display.Stage;
    import flash.events.Event;
    
    import testFolder.TestObject;
    
     public class TestDoc extends MovieClip{
        
        private var obj:TestObject;
        
        public function TestDoc() {
            
            addEventListener(Event.ADDED_TO_STAGE, init, false, 0, true);
        }
            
        private function init(e:Event):void {
            
            removeEventListener(Event.ADDED_TO_STAGE, init);
            
            obj = new TestObject();
            addChild(obj);
        
        }
    }
}

my other class: (notice the package)


package testFolder{
    
    import flash.display.MovieClip;
    import flash.events.Event;
    
    **import Box;**

     public class TestObject extends MovieClip{
        
        public function TestObject() {
            
            addEventListener(Event.ADDED_TO_STAGE, init, false, 0, true);
        }
            
        private function init(e:Event):void {
            
            removeEventListener(Event.ADDED_TO_STAGE, init);
            
            var b:Box = new Box();
            addChild(b);
        
        }
    }
}

this works as it it, BUT if i try to load my document class into another swf and strong type it like so:


var loader:Loader = new Loader();
loader.addEventListener(Event.COMPLETE, onTestComplete);
function onTestComplete(e:Event):void {
    mainSprite.addChild(loader);
    var t:TestDoc = mainSprite.getChildAt(0) as TestDoc;
}

compiler complains:
1046: Type was not found or was not a compile-time constant: Box.
1180: Call to a possibly undefined method Box.
1172: Definition Box could not be found.

whats the problem?