Function prepare_exact_object 

pub fn prepare_exact_object(
    object: &ExactObjectRef,
    value: &impl Serialize,
) -> Result<PreparedExactObject, MembershipPreparationError>

One value prepared for upload: its canonical bytes under the exact object its reference names.

The bytes are not carried beside the value — they are what the value serializes to — so both the validators and the upload paths re-derive them here. PreparedExactObject::new checks them against the reference, so a value that does not serialize to what its reference names fails at this call rather than reaching storage.