Now the fault is that there are not that many interesting specific error conditions in well-designed APIs (e.g., you should not catch a file-not-found error when opening a file to create the file, you should use a OpenIfExistsOtherwiseCreate call instead, O_CREAT in unix-speak.). There are many things that may go wrong which merit their own error codes, descriptions or exception classes but even ImmediateCaller is not interested in most of them.

Once ImmediateCaller is out of the picture, the need for specific exceptions goes away, as UpperLayer won’t be able to do anything reasonable with that specific info. Most of the time the operation just fails or succeeds, and you either roll back or continue. So the necessity to either specify all those low-level errors in your exception specification, or having to map them to something else becomes just an unnecessary burden with no benefits. Especially since mapping them risks losing information.