commerce: deterministic subtotal + jurisdiction-relational tax (20 tests)

price.sx — cart-subtotal (unit price = base + variant delta, default 0),
taxo facts indexed by (jurisdiction, product-class, customer-class) -> bps
queried both directions, apply-bps half-up integer rounding, cart-total
returning {:subtotal :discounts :tax :total} reproducible from
(context, cart). Total 54/54.

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

plans/commerce-on-sx.md

@@ -21,7 +21,7 @@ reconciliation — all auditable via the event log.
 
 ## Status (rolling)
 
-`bash lib/commerce/conformance.sh` → **34/34** (2 suites: catalog, cart)
+`bash lib/commerce/conformance.sh` → **54/54** (3 suites: catalog, cart, price)
 
 ## Ground rules
 
@@ -57,7 +57,7 @@ lib/commerce/api.sx ── (commerce/add) (commerce/total) (commerce/checkout)
 ## Phase 1 — Catalog + cart + deterministic totals
 - [x] `catalog.sx` — product/variant/stock as facts
 - [x] `cart.sx` — line items, add/remove/qty
-- [ ] `price.sx` — base pricing relation, subtotal; tax
+- [x] `price.sx` — base pricing relation, subtotal; tax
 - [ ] `api.sx` + tests + scoreboard + conformance.sh
 
 ## Phase 2 — Promotions (relational)
@@ -76,6 +76,13 @@ lib/commerce/api.sx ── (commerce/add) (commerce/total) (commerce/checkout)
 - [ ] tests: webhook replay, partial refund, double-charge guard
 
 ## Progress log
+- 2026-06-06 — `price.sx`: deterministic `cart-subtotal` (Σ unit×qty, variant
+  delta defaults 0) + jurisdiction-relational tax. `taxo` facts indexed by
+  (jurisdiction, product-class, customer-class)→bps, queried multidirectionally;
+  `apply-bps` rounds half-up with integer arithmetic only. `cart-total` returns
+  `{:subtotal :discounts :tax :total}` (discounts 0 until Phase 2), reproducible
+  from (context, cart). `=` does structural dict equality (order-independent), so
+  total dicts compare directly. price suite 20/20; total 54/54.
 - 2026-06-06 — `cart.sx`: cart as an ordered list of (sku variant qty) lines.
   Pure ops `cart-add` (merges same line / appends), `cart-set-qty` (0 removes),
   `cart-remove`, plus `cart-qty`/`cart-count`/`cart-skus`/`cart-empty?`.