Regardless, there must be a reference against which you can determine that change is occurring. You are saying only the foreground of existence exists, and there is no background. For some strange reason, you seem to be fixated on this thing you call 'interaction', while excluding all else. 'Everything is interaction', you keep saying, while ignoring that which interaction occurs against. When asked about this, you claim the background is simply more interaction. Can't you see how looney this position is?
All things exist against some background. Stars, planets, and other celestial bodies exist within the matrix of space, without which there can be no such bodies. I think the problem is partly that you are trying to conceptualize 'nothingness', as you say: 'there is no such thing as nothingness'. There isn't. It is not something that the mind can encapsulate.
You see the hedge against the background of the hills;
you see the hills against the background of the sky;
but you see the sky against the background of consciousness.
Consciousness does not move; it is just a state. Only mind moves.
Consciousness is before mind. It is limitless and infinite no-thing-ness.
Without it, nothing exists: no thing, no change; no interaction; no universe.
Maybe you just don't see this, but you still have not answered the question as to the beginning and end of what you call 'interaction', so I will answer for you: all interaction, or change, begins and ends against a background of that which does not change. That is the ONLY way there can be any change at all. This should be obvious to anyone.
edit: re the figure/ground image. You do see that there is an implied moving figure against a non-moving, figureless ground, do you not? And that without that non-moving ground, there can be no moving figure?