Hi arg!
One way to do this is to select the circle & rectangle and group them. “Group” is available in the Toolbar area at top of the Hype interface, or in the “Arrange” menu. This grouping shows up under the Timeline area with the default name of “Group”. Then in Hype’s “Metrics” panel set “Content Overflow” (first selection in this panel) for this group to “Hidden”. You will want to make sure the bounding box for the Circle & Rectangle group is adjusted to fit exactly around the perimeter of the Rectangle.