commerce: catalog facts + multidirectional relations + conformance harness (16 tests)

catalog.sx — catalog snapshot (products/variants/stock as fact tuples),
relational accessors (producto/varianto/stocko, derived priceo/classo/
unit-priceo) usable forward and backward, deterministic catalog-price/
-class/-has? helpers. Money is integer minor units. conformance.sh runs
suites on the miniKanren stack and emits scoreboard.{json,md}.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/commerce/catalog.sx

@@ -0,0 +1,83 @@
+;; lib/commerce/catalog.sx — catalog snapshot + relational accessors.
+;;
+;; A catalog snapshot is an immutable dict:
+;;   {:products (list (list sku price class) ...)
+;;    :variants (list (list sku variant delta) ...)
+;;    :stock    (list (list sku variant qty) ...)}
+;;
+;; Money is integer minor units (pence/cents). class is a keyword product
+;; class consumed later by tax and promotion relations. delta is a signed
+;; price adjustment for a variant; qty is on-hand stock for (sku,variant).
+;;
+;; Accessor relations take the snapshot as the first argument and are fully
+;; multidirectional: (producto cat "widget" p c) binds p,c forward;
+;; (producto cat s 1000 c) enumerates every sku priced 1000 backward.
+
+(define empty-catalog {:products (list) :stock (list) :variants (list)})
+
+(define make-catalog (fn (products variants stock) {:products products :stock stock :variants variants}))
+
+(define cat-products (fn (cat) (get cat :products)))
+(define cat-variants (fn (cat) (get cat :variants)))
+(define cat-stock (fn (cat) (get cat :stock)))
+
+;; --- core fact relations ---
+
+(define
+  producto
+  (fn
+    (cat sku price class)
+    (membero (list sku price class) (get cat :products))))
+
+(define
+  varianto
+  (fn
+    (cat sku variant delta)
+    (membero (list sku variant delta) (get cat :variants))))
+
+(define
+  stocko
+  (fn
+    (cat sku variant qty)
+    (membero (list sku variant qty) (get cat :stock))))
+
+;; --- derived relations ---
+
+(define
+  priceo
+  (fn (cat sku price) (fresh (c) (producto cat sku price c))))
+
+(define
+  classo
+  (fn (cat sku class) (fresh (p) (producto cat sku p class))))
+
+;; Effective unit price of a (sku,variant): base + variant delta.
+(define
+  unit-priceo
+  (fn
+    (cat sku variant price)
+    (fresh
+      (base delta)
+      (priceo cat sku base)
+      (varianto cat sku variant delta)
+      (pluso-i base delta price))))
+
+;; --- deterministic lookups (first solution under fixed fact order) ---
+
+(define
+  catalog-price
+  (fn
+    (cat sku)
+    (let
+      ((rs (run 1 p (priceo cat sku p))))
+      (if (empty? rs) nil (first rs)))))
+
+(define
+  catalog-class
+  (fn
+    (cat sku)
+    (let
+      ((rs (run 1 c (classo cat sku c))))
+      (if (empty? rs) nil (first rs)))))
+
+(define catalog-has? (fn (cat sku) (not (nil? (catalog-price cat sku)))))