commerce: composed priced quote (price+promo+stacking) (13 tests)

quote.sx — cart-quote composes the pipeline into a deterministic
{:subtotal :discount :tax :total :codes} with total = subtotal - discount +
tax. Explicit tax policy: tax on gross per-line amounts (discount reduces
payable, not the tax base). This quote is the value the Phase-3 order flow
carries. Total 112/112 across 7 suites.

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` → **99/99** (6 suites: catalog, cart, price, api, promo, stack) — Phases 1-2 done
+`bash lib/commerce/conformance.sh` → **112/112** (7 suites: catalog, cart, price, api, promo, stack, quote) — Phases 1-2 done + priced-quote capstone
 
 ## Ground rules
 
@@ -76,6 +76,13 @@ lib/commerce/api.sx ── (commerce/add) (commerce/total) (commerce/checkout)
 - [ ] tests: webhook replay, partial refund, double-charge guard
 
 ## Progress log
+- 2026-06-07 — `quote.sx` (pricing capstone, bridges Phase 2→3): `cart-quote`
+  composes price+promo+stacking into the deterministic priced quote
+  `{:subtotal :discount :tax :total :codes}` with `total = subtotal - discount
+  + tax`. Explicit tax policy: tax on GROSS per-line amounts (discount reduces
+  payable, not tax base) — documented for the determinism contract. This quote
+  is the value the Phase-3 order flow will carry. quote suite 13/13; total
+  112/112.
 - 2026-06-07 — `stack.sx` (**Phase 2 complete**): stacking precedence as a
   separate selection layer (precedence NOT in the rules, per the miniKanren
   design rule). Exclusivity = unordered code pairs; `valid-stackings` enumerates