Function spec_for_entry 

async fn spec_for_entry(
    source: CatalogueSource,
    entry: &CatalogueEntry,
    download: &Download,
) -> Result<ModelSpec, String>

The spec one feed entry describes for the quant a row draws: where the file is, the entry’s own byte length, the digest where its host publishes one, and the facts both carry.

The Hub’s entries carry the URL and the digest themselves; the speech feed’s carry neither, so its documents are read for the link - which is also where that feed’s files’ only verification (the byte length) comes from.