Splendid graphics, Peter! Looks like a stringer to me. As to which one, we have plenty of choice. If it failed concurrently with everything else, would it not be in the South China Sea right now? This seems to suggest that it got wedged inside at this interesting angle before the failure of the skin.
Except if it failed at a rivet line along the skin then the outer skin is compromised as well.
I am still hoping that some of our graphics artists could transpose that fuzzy piece in the incident picture to overlay the clear interior reference photo that Machaca posted.