Function conv_expr 

pub fn conv_expr(access: &str, ty: &Type, known: &BTreeSet<String>) -> String

Conversion expression for a field/payload access of type ty. Identity (move) when the type holds no user type (generated and author types are then identical); otherwise .into() (user type), or a map/into_iter().map() recursing through Option/Vec. Symmetric — works generated→author and author→generated, since From is generated both ways. Public so the macro’s adapter reuses the exact same boundary conversions.