Help!
John was right on! The small screw attaching one of the two rocker shaped bits of metal inside the shock tube came loose, and lodged between the shock tube and the frame tube, actually almost puncturing through the metal causing the dimple.
My problem now, is that I can't get the shock tube out of the frame tube so that I can chase down and reinstall the screw (which is now in the main body tube).
The black-caps of the tube seemingly preventing my removal of the shock tube don't seem to be unscrewable, from my initial exploratory efforts with a rubber loop pipe wrench. Before I came at it with an actual pipe wrench, I thought that I would pause and get some advice, since I have absolutely no idea what I'm doing here.
Any advice would be most welcome at this point!