Function validate_document_interfaces 

pub fn validate_document_interfaces(
    referenced_rules: &HashMap<Vec<String>, HashSet<String>>,
    doc_ref_facts: &[(FactPath, String, Source)],
    rule_entries: &IndexMap<RulePath, RuleEntryForBindingCheck>,
    all_docs: &[LemmaDoc],
    sources: &HashMap<String, String>,
) -> Result<(), Vec<LemmaError>>

Validate that every doc-ref fact path’s referenced document has the required rules and that each such rule’s result type satisfies what the referencing rules expect. Type errors are reported at the binding fact’s source when a binding changed the doc ref.