One reference's cache entry: what the script its fetch recipe names last answered for it, and when. How an entry is filled, refreshed and served is YmerNode.References.Cache's; this is the row.

Shape decisions:

• One entry per reference, held by it: the reference's delete takes the row with it, and the unique index refuses a second.
• The content sits in exactly one of body (text, in the node database) or path (a file, relative to the cache directory) — which one follows the script's cache declaration. A database CHECK refuses both and neither.
• format is the media type the script answered, and it alone decides how the entry is served — never where the bytes are kept.
• script names the script that filled the entry. A reference_validator means something only to the script that issued it, so an entry filled by another script than the one the recipe names today is not handed to the new one.
• uri and fragment are the target the entry was fetched for — the reference's at that moment. An entry whose target is not the one the reference names now is a miss, whatever wrote it.
• An empty body is a page with no text, and is kept as one: the changeset casts no value to nil, so "" is a body and not an absent one.
• fetched_at is when the content last changed as far as the node knows — the last full answer — and checked_at when the script was last asked, which an unchanged answer moves alone.