> Rust lacks a uniform error type.

Not quite true. The unifying error trait is std::error::Error.

> pain when you have to pass them upward through a chain of calls

Kind of? You just make an enum with the various variants that need to be passed through and use the #[from] macro to generate the conversion code automatically.

It’s more characters than eg. A union type in Python or TypeScript, but it’s not much more.

Plus, it makes you think about your error design, which is important!