Function contact_shape_error 

pub fn contact_shape_error(contacts: &[String]) -> Option<ContactRejection>

The shape check behind [validate_contacts], returning the reason rather than a Problem.

Split out because Problem’s fields are private, so the web admin — which answers in its own error shape and not in application/problem+json — could not read the detail back out of one. Sharing the check rather than writing a second one is what keeps PATCH /api/accounts/{id} from accepting a contact newAccount would have refused.