feat(POS-008): completed feature

work/artifacts/POS-008/reviewer.json

@@ -0,0 +1,15 @@
+{
+  "feature_id": "POS-008",
+  "agent": "reviewer",
+  "stage": "review_gate",
+  "verdict": "APPROVED",
+  "summary": "POST /pos/sales idempotent atomic transaction. tsc 0, verify green.",
+  "checks": [
+    {"item": "Idempotency", "ok": true, "evidence": "EXISTS check on idempotency_key; returns existing"},
+    {"item": "Transaction", "ok": true, "evidence": "BEGIN/COMMIT/ROLLBACK + FOR UPDATE lock"},
+    {"item": "Totals validation", "ok": true, "evidence": "subtotal/tax/total computed; payment >= total"},
+    {"item": "Cash session update", "ok": true, "evidence": "expected_cash_cents += tendered cash"},
+    {"item": "tsc/verify", "ok": true, "evidence": "tsc 0, verify green"}
+  ],
+  "issues": []
+}