commerce: order ledger on persist + idempotent reconciliation (20 tests)

ledger.sx — each order is an append-only persist stream "order/<id>";
status/total/paid/recon are folds over events (ledger = source of truth).
order-pay / order-refund are idempotent via persist/append-once keyed on the
payment ref, so a replayed SumUp webhook records once. order-recon-of
classifies unpaid/ok/underpaid/overpaid on net vs total; ledger-mismatches
finds genuine paid != ordered across streams. minikanren+scheme/flow+persist
verified coexisting in one process. Total 132/132 across 8 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` → **112/112** (7 suites: catalog, cart, price, api, promo, stack, quote) — Phases 1-2 done + priced-quote capstone
+`bash lib/commerce/conformance.sh` → **132/132** (8 suites: catalog, cart, price, api, promo, stack, quote, ledger) — Phases 1-2 done; Phase 3 ledger done
 
 ## Ground rules
 
@@ -68,7 +68,7 @@ lib/commerce/api.sx ── (commerce/add) (commerce/total) (commerce/checkout)
 ## Phase 3 — Order lifecycle (flow + store)
 - [ ] order flow: reserve stock → await payment → fulfil
 - [ ] payment webhook resumes the suspended flow
-- [ ] order ledger as a `persist` stream; idempotent reconciliation
+- [x] order ledger as a `persist` stream; idempotent reconciliation
 
 ## Phase 4 — Reconciliation + federation
 - [ ] mismatch detection (paid≠ordered) as queries over the ledger
@@ -76,6 +76,17 @@ lib/commerce/api.sx ── (commerce/add) (commerce/total) (commerce/checkout)
 - [ ] tests: webhook replay, partial refund, double-charge guard
 
 ## Progress log
+- 2026-06-07 — `ledger.sx` (Phase 3 piece, checkbox 3): order ledger as a
+  persist event stream "order/<id>". Status/total/paid/recon are projections
+  (folds) over events — ledger is the single source of truth. `order-pay`/
+  `order-refund` are idempotent via `persist/append-once` keyed on the payment
+  ref, so a replayed SumUp webhook records once (no double-charge). `order-recon-of`
+  classifies :unpaid/:ok/:underpaid/:overpaid on net (paid−refunded) vs total;
+  `ledger-mismatches` finds genuine paid≠ordered across all streams. Verified
+  minikanren+scheme/flow+persist all coexist in one sx_server process. ledger
+  suite 20/20; total 132/132. Next: order flow (reserve→pay→fulfil) as a Scheme
+  flow-on-sx flow with webhook resume (checkboxes 1-2) — needs SX↔Scheme quote
+  marshalling.
 - 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