These sounds like exceptions rather than errors to me. Difference being, exceptions truly are exceptional and not anticipated; like running out of memory. How do you even handle that? Would probably let it crash and restart (Erlang model). Errors is something you anticipate can happen, such as getting 4xx-5xx back from the server and know what to do in those cases.

Then it's fair to say that you definitely can't get an error by adding two numbers.

> How do you even handle that?

You request a smaller block of memory? Not everyone is always requesting the minimum they need right now.

> Would probably let it crash and restart (Erlang model)

The Erlang model is to let a partial failure trigger a less complex part of the system to resume that logic based on a strategy.

> Then it's fair to say that you definitely can't get an error by adding two numbers.

I mean, you can also accept garbage back, I guess?