Function compare_graphql_contracts 

pub fn compare_graphql_contracts(
    before: &GraphqlDocument,
    after: &GraphqlDocument,
) -> CompatibilityReport

Compares GraphQL schemas and persisted operations using conservative breaking-change rules.

Missing types/fields/enum values, new required arguments, narrowed types, and invalidated persisted operations are breaking. Incomplete extraction returns CompatibilityStatus::Unknown.