Hopefully these conversations help the developers and are thought provoking.
If you (a programmer) have a modeling error and you have two complete data sets to look at, you can start to analyze and highlight faces or give visual feedback using coordinates from both models. You would have reference placement for everything. You could get a visual face from the prior model and bring it into the current model (highlighted) to display an error, for instance.
Another advantage is almost a free "Revert" button, you wouldn't have to recompute the model, just reload the prior. We could swap between the current and the prior.
Sometime those "genuine" fails are FreeCAD errors and only sometimes OCC.
This adds more possible errors.
It just seems to me
that a good starting place to recover from an error is to have a good path back to a valid model. Something easy to reference without using an algorithm to figure out where things used to be. I know if I had to tackle error handling in CAD that's what I would want.