more

cmd/cart/pool-server.go

@@ -75,6 +75,7 @@ func (s *PoolServer) GetCartHandler(w http.ResponseWriter, r *http.Request, id c
 
 func (s *PoolServer) AddSkuToCartHandler(w http.ResponseWriter, r *http.Request, id cart.CartId) error {
 	sku := r.PathValue("sku")
+	country := getCountryFromHost(r.Host)
 	if s.idx != nil && s.idx.IsDeleted(sku) {
 		// Bus-deleted SKU — skip the HTTP fetch and reject the add. Mirrors the
 		// product-fetcher's "product service returned %d for sku %s" shape so
@@ -86,13 +87,28 @@ func (s *PoolServer) AddSkuToCartHandler(w http.ResponseWriter, r *http.Request,
 		http.Error(w, fmt.Sprintf("product service returned %d for sku %s (bus-deleted)", 404, sku), http.StatusNotFound)
 		return nil
 	}
-	msg, err := GetItemAddMessage(r.Context(), sku, 1, getCountryFromHost(r.Host), nil)
-	if err != nil {
-		return err
-	}
+
+	// Cache-only fast path: AddSkuToCartHandler is a SINGLE top-level add
+	// (qty=1, no children). When the projection carries full authoritative
+	// fields, we skip PRODUCT_BASE_URL entirely and build the AddItem
+	// directly from the cache. This eliminates one HTTP round-trip per
+	// add-to-cart under steady-state bus-fed conditions.
+	var msg *messages.AddItem
 	if s.idx != nil {
-		if p, ok := s.idx.Get(sku); ok {
-			ApplyProjectionOverlay(msg, p)
+		if p, ok := s.idx.Get(sku); ok && HasRequiredFields(p) {
+			msg = BuildAddItemFromCache(sku, 1, country, nil, p)
+		}
+	}
+	if msg == nil {
+		var err error
+		msg, err = GetItemAddMessage(r.Context(), sku, 1, country, nil)
+		if err != nil {
+			return err
+		}
+		if s.idx != nil {
+			if p, ok := s.idx.Get(sku); ok {
+				ApplyProjectionOverlay(msg, p)
+			}
 		}
 	}