chore(checkpoint): save club core backend and pending pos fixes

work/artifacts/POS-RECEIPT-QUICK-FIXES/qa.json

@@ -0,0 +1,28 @@
+{
+  "feature_id": "POS-RECEIPT-QUICK-FIXES",
+  "agent": "qa",
+  "stage": "qa_gate",
+  "verdict": "APPROVED",
+  "qa_check": "qa",
+  "summary": "QA aprobado: el fix cubre los dos síntomas reportados (IVA del ticket TPV a 0 y error de stock/JSON confuso en checkout) y no rompe builds ni validaciones base.",
+  "test_results": {
+    "automated": [
+      "./scripts/verify.sh ✅",
+      "cd project && npx vitest run src/modules/pos/tests/payment-allocation.test.ts ✅",
+      "cd project/apps/pos && npm run build ✅",
+      "cd project/frontend && npm run build ✅"
+    ],
+    "traceability": [
+      "POS receipts/returns now derive and render IVA from pricing data instead of persisting taxCents=0.",
+      "Frontend checkout now reconciles server cart quantities with PATCH/DELETE, preventing accidental quantity inflation before POST /checkout.",
+      "Checkout proxy now surfaces the backend human message instead of returning the raw JSON envelope to the UI."
+    ],
+    "blocked_or_manual": [
+      "Targeted DB integration tests for POS receipts/returns remain blocked by the pre-existing migration 057 error (`type \"w\" does not exist`).",
+      "Recomendable smoke manual en entorno: vender un producto con IVA, imprimir ticket y validar línea IVA>0; luego reproducir checkout con carrito previo para confirmar que ya no se incrementa la cantidad en servidor."
+    ]
+  },
+  "notes": [
+    "La cobertura automatizada disponible para esta sesión es suficiente para aprobar el hotfix, con la limitación conocida de la migración rota no introducida por estos cambios."
+  ]
+}