Exception instance being thrown should have been caught or constructed locally

Any exception instance being thrown should have been either constructed or caught in the current scope. If it came from anywhere else (passed in as argument, was stored in a field...) then the stack trace will be mystifying, and the simple remedy is to chain that exception into a new one so you get a new stack trace as well.

(If we research this I imagine we will probably find we need a few more special case exemptions.)