This was part of the original request of SERVER-91246, but was not completed as described:

Certain keystring decoding errors throw exceptions like this one.

Including the full keystring in the error message would be a significant debugging aid when we see validation failures in this area.

Additionally, if an exception like this is thrown, it prevents us from advancing our cursor, but we should still try to add context about the document, if possible, and continue with validation on other indexes.