Complete refactor to new grpc control plane and only http proxy for carts (#4)

Co-authored-by: matst80 <mats.tornberg@gmail.com>
Reviewed-on: https://git.tornberg.me/mats/go-cart-actor/pulls/4
Co-authored-by: Mats Törnberg <mats@tornberg.me>
Co-committed-by: Mats Törnberg <mats@tornberg.me>

cmd/cart/mutation_remove_delivery.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"fmt"
+
+	messages "git.tornberg.me/go-cart-actor/pkg/messages"
+)
+
+// mutation_remove_delivery.go
+//
+// Registers the RemoveDelivery mutation.
+//
+// Behavior:
+//   - Removes the delivery entry whose Id == payload.Id.
+//   - If not found, returns an error.
+//   - Cart totals are recalculated (WithTotals) after removal.
+//   - Items previously associated with that delivery simply become "without delivery";
+//     subsequent delivery mutations can reassign them.
+//
+// Differences vs legacy:
+//   - Legacy logic decremented TotalPrice explicitly before recalculating.
+//     Here we rely solely on UpdateTotals() to recompute from remaining
+//     deliveries and items (simpler / single source of truth).
+//
+// Future considerations:
+//   - If delivery pricing logic changes (e.g., dynamic taxes per delivery),
+//     UpdateTotals() may need enhancement to incorporate delivery tax properly.
+
+func RemoveDelivery(g *CartGrain, m *messages.RemoveDelivery) error {
+	if m == nil {
+		return fmt.Errorf("RemoveDelivery: nil payload")
+	}
+	targetID := uint32(m.Id)
+	index := -1
+	for i, d := range g.Deliveries {
+		if d.Id == targetID {
+			index = i
+			break
+		}
+	}
+	if index == -1 {
+		return fmt.Errorf("RemoveDelivery: delivery id %d not found", m.Id)
+	}
+
+	// Remove delivery (order not preserved beyond necessity)
+	g.Deliveries = append(g.Deliveries[:index], g.Deliveries[index+1:]...)
+	g.UpdateTotals()
+	return nil
+}