Show a store's products — the store's public catalog as typed data, one row per product: name, description, price in USD and in Coms (1 Com = $0.01), category, stock (in_stock + available), a picture served from this gateway's own origin (null when the product has none), and the product's own pay link. Hosts that support MCP Apps draw the result as the ComOS shop panel: product cards with pictures, filters, and a Buy button that opens the pay link — the panel never places an order. Pass tenant_id (e.g. "earth"). A tenant that is not a storefront answers { error: "not_a_storefront" }. Public, read-only, free. CO 607-002. Returns: { tenant_id, store_name, storefront, read_at, products: [{ product_id, name, description, price, currency, coms, category, in_stock, available, image_url, pay_url }] } — also as structuredContent. A tenant that is not a storefront: isError with { error: "not_a_storefront", tenant_id }. Example: call federation_shop with arguments {"tenant_id":""}.