Since it took me a moment to figure out why the extra incref was needed:

* both PyException_SetCause and PyException_SetContext steal a reference to their second argument
* hence we need the second incref, rather than relying solely on the reference received from PyErr_NormalizeException

This does suggest the new incref is conceptually in the wrong spot - it should be before the call to PyException_SetCause, such that this block of code *always* possesses a valid reference while accessing "val". At the moment, we technically still don't have an active reference when passing "val" to PyException_SetContext.