Enriched product feeds

Retailer product feeds that carry a product_evidence block: licensed, attributed citations about each product from an evidence provider, plus a signed attribution token from an attribution network. Three routes deliver the same block so each platform can see its own path working.

Route A
The block sits in the protocol's custom metadata. UCP: metadata.product_evidence. ACP: top-level field, pending a slot in the spec.
Route B
The block is encoded at the end of the product description. Works today on any feed.
Route C
A companion feed keyed on the canonical product id, joined to the untouched retailer feed.

JSON Schema. Validate any feed here with pnpm validate <url> --route A|B|C from the geodesix-shopping-agent repo.