deduplication

The best solution here is a map, using keys as the set. So something like:

func dedup(arr []T) (ret []T) {
    m := make(map[T]bool)
    for _, t := range T {
        m[t] = true
    }
    
    // optimization: make ret the right size
    for t := range m {
        ret = append(ret, t)
    }
}

I haven't used Go's new generics, but I'm guessing this would work fine, provided T is a value type (or can be converted to one). If you know you need deduplication at the start, just use a map at the start.

If you don't have value types, you're going to have a hard time regardless of language (would probably need some OOP features, which adds a ton of complexity). But you can get pretty far with that pattern. If you add a Hash() int to your type:

func dedup(are []T) (ret []T) {
    m := make(map[int]bool)
    for _, t := range arr {
        h := t.Hash()
        if !m[h] {
            m[h] = true
            ret = append(ret, t)
        }
    }
}

err... people just did not print any of the relevant information in error cases

That's what error wrapping is for:

if err != nil {
    return fmt.Errorf("context: %w", err)
}

This makes it so you can use the errors package to unwrap errors or check if an error is a given type. Or you can propagate it like I've shown above.

So I see this as programmer error. Rust has the same issue since it's easy to just throw a ? in there and bail early without additional context. The simpler form is easier to catch in Go vs Rust in a code review because it's more verbose.

It seems you don't like verbosity, which is fair. I'm fine with verbosity, I don't like surprises, and Go has enough of those that I generally avoid it.