I tend to follow the rest of the ecosystem when developing libraries. If i wanted to make a zig lib id look at what other major libs are doing (or not doing) and copy that.
If i found no consistency id be making a post like OP but from a different perspective.
Library developers tend to choose the path of least resistance, which is to not pass diagnostic information.
The most convenient diagonistic system is the good old logging. Logging is easy.
Maybe logging will be the de facto solution of passing error data in Zig ecosystem, due to psychological reasons.