Function validate 

pub fn validate(doc: &Document) -> ValidationReport

Run the full document validation pass against the document’s own in-file diagnostic policy and in-file brand contract.

This is a thin wrapper over validate_with_policy that passes doc.diagnostic_policy and &doc.brand_contract. It preserves the historical contract exactly: a document with no diagnostics { … } or brand { … } block carries empty defaults, which are identity passes, so the output is byte-identical to running validation with no config at all.