Function format_validation_kind 

pub(crate) fn format_validation_kind(
    kind: &ValidationErrorKind,
    source: &str,
    primary_range: &Range<usize>,
) -> (String, Vec<String>, Vec<Suggestion>)

Build the (message, footers, suggestions) triple for a validation kind.

For *Mismatch variants the suggestion is a single replacement that rewrites the declared identifier to the expected one. Other variants surface only the message and any upstream help() text.