> Beyond these concerns, I also don't love enums for errors because it means adding any new error type will be a breaking change. I don't love the idea of committing to that, but maybe I'm overthinking?

Is it a new error condition that downstream consumers want to know about so they can have different logic? Add the enum variant. The entire point of this pattern is to do what typed exceptions in Java were supposed to do, give consuming code the ability to reason about what errors to expect, and handle them appropriately if possible.

If your consumer can't be reasonably expected to recover? Use a generic failure variant, bonus points if you stuff the inner error in and implement std::Error so consumers can get the underlying error by calling .source() for debugging at least.

> By contrast, I just wrap Go errors with `fmt.Errorf("opening file `%s`: %w", filePath, err)` and handle any special error cases with `errors.As()` and similar and move on with life. It maybe doesn't feel _elegant_, but it lets me get stuff done.

Nothing stopping you from doing the same in Rust, just add a match arm with a wildcard pattern (_) to handle everything but your special cases.

In fact, if you suspect you are likely to add additional error variants, the `#[non_exhaustive]` attribute exists explicitly to handle this. It will force consumers to provide a match arm with a wildcard pattern to prevent additions to the enum from causing API incompatibility. This does come with some other limitations, so RTFM on those, but it does allow you to add new variants to an Error enum without requiring a major semver bump.