fix(marketplace): adapt to nullable PurchaseHistoryRecord.MonthlyCost

After rebasing onto feat/multicloud-web-frontend, base PR #258 made
PurchaseHistoryRecord.MonthlyCost a *float64 (nullable). The marketplace
default price-schedule path passed it as a float64. Dereference it
nil-safely at the call site, treating an absent monthly breakdown as a
zero recurring contribution to residual value (per the nullable-not-zero
convention: nil means "no breakdown recorded", which contributes nothing
to the residual list price).

Author: cristim

internal/api/handler_marketplace.go

@@ -138,8 +138,14 @@ func (h *Handler) marketplaceList(ctx context.Context, req *events.LambdaFunctio
 	// rather than the full contract term (which overprices older RIs).
 	remainingMonths := computeRemainingMonths(row.Timestamp, row.Term)
 
-	// Validate and normalise the price schedule.
-	schedule, err := resolveMarketplacePriceSchedule(body.PriceSchedule, remainingMonths, row.UpfrontCost, row.MonthlyCost)
+	// Validate and normalise the price schedule. A nil MonthlyCost means the
+	// provider recorded no recurring breakdown (issue #258 made the field
+	// nullable); treat absent as zero recurring contribution to residual value.
+	monthlyCost := 0.0
+	if row.MonthlyCost != nil {
+		monthlyCost = *row.MonthlyCost
+	}
+	schedule, err := resolveMarketplacePriceSchedule(body.PriceSchedule, remainingMonths, row.UpfrontCost, monthlyCost)
 	if err != nil {
 		return nil, NewClientError(400, err.Error())
 	}