Function create_appointment 

pub fn create_appointment(
    adapter: &dyn DatabaseOperations,
    config: &DbBackendConfig,
    schema: &AppSchema,
    request: &AppointmentCreate<'_>,
) -> Result<i64, DatabaseError>

Creates a confirmed appointment with adapter-owned overlap serialization. All related reads are bounded; account, session, and unrelated business state never enter the transaction view.