Function transform_index_payload 

pub fn transform_index_payload(roots_spec: &str) -> Value

Build the transform-index catalogue from a root[:root…] spec (paths relative to the current directory): every registered manifest, as JSON, under the contract version. The published contract carries a snapshot of this document and consumers of the registry assert against it, so a registry change cannot silently diverge from the contract. (The description text is part of that snapshot; changing it is a contract change.)