In my personal experience distinct handling of errors like these does indeed come up significantly more rarely. What ends up mattering to me much more often is how these errors are presented to the user, or what ends up in the logs in production. In those cases something like

    error: failed to read contents of `foo`
      caused by: a physical I/O error has occurred (...)

and

    error: failed to open `foo`
      caused by: permission denied (...)

are significantly more actionable than just the underlying I/O errors by themselves. To the point where a person reading these messages has a shot at addressing the problem without any prior knowledge of the code base.

In `anyhow` adding such context via its `context` family of methods seems fairly well accepted. I hope that my comment demonstrates there's no reason why `enum` based approach would need to be any worse than what `anyhow` can achieve.