This implies that every function in your library that ever has to do anything that might error out - e.g. integer arithmetic or array indexing - has to be declared as returning the corresponding Result to propagate the error. Which means that you are now imposing this requirement (to check for internal logic bugs in library code) onto the user of your library.
Well, I don't write as huge a code as this though, nor does it have as many layers.
Usually I just use the `?` and `.map_err` (or `anyhow` / `thiserror`) to delegate and move on with life.
I have a few places where I do pattern-matches to avoid exactly what you described: imposing the extra internal complexity to users. Which is indeed a bad thing and I am trying to fight it. Not always succeeding.
