major changes

cmd/cart/k8s-host-discovery.go

@@ -3,8 +3,6 @@ package main
 import (
 	"log"
 
-	"git.k6n.net/go-cart-actor/pkg/actor"
-	"git.k6n.net/go-cart-actor/pkg/cart"
 	"git.k6n.net/go-cart-actor/pkg/discovery"
 	v1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/client-go/kubernetes"
@@ -32,7 +30,7 @@ func GetDiscovery() discovery.Discovery {
 	})
 }
 
-func UseDiscovery(pool actor.GrainPool[*cart.CartGrain]) {
+func UseDiscovery(pool discovery.DiscoveryTarget) {
 
 	go func(hw discovery.Discovery) {
 		if hw == nil {

cmd/cart/main.go

@@ -178,7 +178,7 @@ func main() {
 
 			return nil
 		},
-		SpawnHost: func(host string) (actor.Host, error) {
+		SpawnHost: func(host string) (actor.Host[cart.CartGrain], error) {
 			return proxy.NewRemoteHost[cart.CartGrain](host)
 		},
 		TTL:      5 * time.Minute,
@@ -201,7 +201,7 @@ func main() {
 	mux := http.NewServeMux()
 	debugMux := http.NewServeMux()
 
-	grpcSrv, err := actor.NewControlServer[*cart.CartGrain](controlPlaneConfig, pool)
+	grpcSrv, err := actor.NewControlServer[cart.CartGrain](controlPlaneConfig, pool)
 	if err != nil {
 		log.Fatalf("Error starting control plane gRPC server: %v\n", err)
 	}

cmd/cart/pool-server.go

@@ -41,13 +41,13 @@ var (
 )
 
 type PoolServer struct {
-	actor.GrainPool[*cart.CartGrain]
+	actor.GrainPool[cart.CartGrain]
 	pod_name           string
 	inventoryService   inventory.InventoryService
 	reservationService inventory.CartReservationService
 }
 
-func NewPoolServer(pool actor.GrainPool[*cart.CartGrain], pod_name string, inventoryService inventory.InventoryService, inventoryReservationService inventory.CartReservationService) *PoolServer {
+func NewPoolServer(pool actor.GrainPool[cart.CartGrain], pod_name string, inventoryService inventory.InventoryService, inventoryReservationService inventory.CartReservationService) *PoolServer {
 	srv := &PoolServer{
 		GrainPool:          pool,
 		pod_name:           pod_name,
@@ -58,7 +58,7 @@ func NewPoolServer(pool actor.GrainPool[*cart.CartGrain], pod_name string, inven
 	return srv
 }
 
-func (s *PoolServer) ApplyLocal(ctx context.Context, id cart.CartId, mutation ...proto.Message) (*actor.MutationResult[*cart.CartGrain], error) {
+func (s *PoolServer) ApplyLocal(ctx context.Context, id cart.CartId, mutation ...proto.Message) (*actor.MutationResult[cart.CartGrain], error) {
 	return s.Apply(ctx, uint64(id), mutation...)
 }
 
@@ -460,10 +460,7 @@ func (s *PoolServer) InternalApplyMutationHandler(w http.ResponseWriter, r *http
 func (s *PoolServer) GetAnywhere(ctx context.Context, cartId cart.CartId) (*cart.CartGrain, error) {
 	id := uint64(cartId)
 	if host, isOnOtherHost := s.OwnerHost(id); isOnOtherHost {
-		grain := &cart.CartGrain{}
+		return host.Get(ctx, id)
-
-		err := host.Get(ctx, id, grain)
-		return grain, err
 	}
 	return s.Get(ctx, id)
 }

cmd/checkout/adyen-handlers.go

@@ -57,13 +57,13 @@ type SessionRequest struct {
 
 // }
 
-func getCheckoutIdFromNotificationItem(item webhook.NotificationRequestItem) (uint64, error) {
+func getCheckoutIdFromNotificationItem(item webhook.NotificationRequestItem) (*cart.CartId, error) {
 	cartId, ok := cart.ParseCartId(item.MerchantReference)
 	if !ok {
 		log.Printf("The notification does not have a valid cartId: %s", item.MerchantReference)
-		return 0, errors.New("invalid cart id")
+		return nil, errors.New("invalid cart id")
 	}
-	return uint64(cartId), nil
+	return &cartId, nil
 }
 
 func (s *CheckoutPoolServer) AdyenHookHandler(w http.ResponseWriter, r *http.Request) {
@@ -105,7 +105,7 @@ func (s *CheckoutPoolServer) AdyenHookHandler(w http.ResponseWriter, r *http.Req
 
 				// If successful, apply payment completed
 				//if isSuccess {
-				if err := s.applyAnywhere(r.Context(), checkoutId,
+				if err := s.ApplyAnywhere(r.Context(), *checkoutId,
 					&messages.PaymentEvent{
 						PaymentId: item.PspReference,
 						Success:   isSuccess,
@@ -154,7 +154,7 @@ func (s *CheckoutPoolServer) AdyenHookHandler(w http.ResponseWriter, r *http.Req
 						Message:   item.Reason,
 					})
 				}
-				if err := s.applyAnywhere(r.Context(), checkoutId, msgs...); err != nil {
+				if err := s.ApplyAnywhere(r.Context(), *checkoutId, msgs...); err != nil {
 					log.Printf("error applying authorization event: %v", err)
 					http.Error(w, err.Error(), http.StatusInternalServerError)
 					return
@@ -165,7 +165,7 @@ func (s *CheckoutPoolServer) AdyenHookHandler(w http.ResponseWriter, r *http.Req
 
 					pspReference := item.PspReference
 					uid := uuid.New().String()
-					ref := cart.CartId(checkoutId).String()
+					ref := checkoutId.String()
 					req := service.ModificationsApi.CaptureAuthorisedPaymentInput(pspReference).IdempotencyKey(uid).PaymentCaptureRequest(adyenCheckout.PaymentCaptureRequest{
 						Amount:          adyenCheckout.Amount(item.Amount),
 						MerchantAccount: "ElgigantenECOM",
@@ -176,7 +176,7 @@ func (s *CheckoutPoolServer) AdyenHookHandler(w http.ResponseWriter, r *http.Req
 						log.Printf("Error capturing payment: %v", err)
 					} else {
 						log.Printf("Payment captured successfully: %+v", res)
-						s.Apply(r.Context(), checkoutId, &messages.OrderCreated{
+						s.ApplyAnywhere(r.Context(), *checkoutId, &messages.OrderCreated{
 							OrderId: res.PaymentPspReference,
 							Status:  item.EventCode,
 						})
@@ -191,7 +191,7 @@ func (s *CheckoutPoolServer) AdyenHookHandler(w http.ResponseWriter, r *http.Req
 					log.Printf("Could not get checkout id: %v", err)
 
 				} else {
-					if err := s.applyAnywhere(r.Context(), checkoutId, &messages.PaymentEvent{
+					if err := s.ApplyAnywhere(r.Context(), *checkoutId, &messages.PaymentEvent{
 						PaymentId: item.PspReference,
 						Success:   isSuccess,
 						Name:      item.EventCode,

cmd/checkout/k8s-host-discovery.go

@@ -3,8 +3,6 @@ package main
 import (
 	"log"
 
-	"git.k6n.net/go-cart-actor/pkg/actor"
-	"git.k6n.net/go-cart-actor/pkg/checkout"
 	"git.k6n.net/go-cart-actor/pkg/discovery"
 	v1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/client-go/kubernetes"
@@ -32,7 +30,7 @@ func GetDiscovery() discovery.Discovery {
 	})
 }
 
-func UseDiscovery(pool actor.GrainPool[*checkout.CheckoutGrain]) {
+func UseDiscovery(pool discovery.DiscoveryTarget) {
 
 	go func(hw discovery.Discovery) {
 		if hw == nil {

cmd/checkout/klarna-handlers.go

@@ -195,7 +195,7 @@ func (s *CheckoutPoolServer) KlarnaPushHandler(w http.ResponseWriter, r *http.Re
 		})
 	}
 
-	s.applyAnywhere(r.Context(), uint64(grain.Id), &messages.PaymentCompleted{
+	s.ApplyAnywhere(r.Context(), grain.Id, &messages.PaymentCompleted{
 		PaymentId:          orderId,
 		Status:             "completed",
 		ProcessorReference: &order.ID,
@@ -267,7 +267,7 @@ func (a *CheckoutPoolServer) getGrainFromKlarnaOrder(ctx context.Context, order
 	if !ok {
 		return nil, fmt.Errorf("invalid cart id in order reference: %s", order.MerchantReference1)
 	}
-	grain, err := a.getAnywhere(ctx, uint64(cartId))
+	grain, err := a.GetAnywhere(ctx, cartId)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get cart grain: %w", err)
 	}

cmd/checkout/main.go

@@ -89,7 +89,7 @@ func main() {
 		Destroy: func(grain actor.Grain[checkout.CheckoutGrain]) error {
 			return nil
 		},
-		SpawnHost: func(host string) (actor.Host, error) {
+		SpawnHost: func(host string) (actor.Host[checkout.CheckoutGrain], error) {
 			return proxy.NewRemoteHost[checkout.CheckoutGrain](host)
 		},
 		TTL:      1 * time.Hour, // Longer TTL for checkout
@@ -121,7 +121,7 @@ func main() {
 		log.Fatalf("no connection to amqp defined")
 	}
 
-	grpcSrv, err := actor.NewControlServer[*checkout.CheckoutGrain](controlPlaneConfig, pool)
+	grpcSrv, err := actor.NewControlServer[checkout.CheckoutGrain](controlPlaneConfig, pool)
 	if err != nil {
 		log.Fatalf("Error starting control plane gRPC server: %v\n", err)
 	}

cmd/checkout/pool-server.go

@@ -46,7 +46,7 @@ var (
 )
 
 type CheckoutPoolServer struct {
-	actor.GrainPool[*checkout.CheckoutGrain]
+	actor.GrainPool[checkout.CheckoutGrain]
 	pod_name         string
 	klarnaClient     *KlarnaClient
 	adyenClient      *adyen.APIClient
@@ -54,7 +54,7 @@ type CheckoutPoolServer struct {
 	inventoryService *inventory.RedisInventoryService
 }
 
-func NewCheckoutPoolServer(pool actor.GrainPool[*checkout.CheckoutGrain], pod_name string, klarnaClient *KlarnaClient, cartClient *CartClient, adyenClient *adyen.APIClient) *CheckoutPoolServer {
+func NewCheckoutPoolServer(pool actor.GrainPool[checkout.CheckoutGrain], pod_name string, klarnaClient *KlarnaClient, cartClient *CartClient, adyenClient *adyen.APIClient) *CheckoutPoolServer {
 	srv := &CheckoutPoolServer{
 		GrainPool:    pool,
 		pod_name:     pod_name,
@@ -66,7 +66,7 @@ func NewCheckoutPoolServer(pool actor.GrainPool[*checkout.CheckoutGrain], pod_na
 	return srv
 }
 
-func (s *CheckoutPoolServer) ApplyLocal(ctx context.Context, id checkout.CheckoutId, mutation ...proto.Message) (*actor.MutationResult[*checkout.CheckoutGrain], error) {
+func (s *CheckoutPoolServer) ApplyLocal(ctx context.Context, id checkout.CheckoutId, mutation ...proto.Message) (*actor.MutationResult[checkout.CheckoutGrain], error) {
 	return s.Apply(ctx, uint64(id), mutation...)
 }
 
@@ -90,7 +90,7 @@ func (s *CheckoutPoolServer) SetDeliveryHandler(w http.ResponseWriter, r *http.R
 		return err
 	}
 
-	return s.WriteResult(w, result.Result)
+	return s.WriteResult(w, result)
 }
 
 func (s *CheckoutPoolServer) RemoveDeliveryHandler(w http.ResponseWriter, r *http.Request, id checkout.CheckoutId) error {
@@ -108,7 +108,7 @@ func (s *CheckoutPoolServer) RemoveDeliveryHandler(w http.ResponseWriter, r *htt
 		return err
 	}
 
-	return s.WriteResult(w, result.Result)
+	return s.WriteResult(w, result)
 }
 
 func (s *CheckoutPoolServer) SetPickupPointHandler(w http.ResponseWriter, r *http.Request, id checkout.CheckoutId) error {
@@ -122,7 +122,7 @@ func (s *CheckoutPoolServer) SetPickupPointHandler(w http.ResponseWriter, r *htt
 		return err
 	}
 
-	return s.WriteResult(w, result.Result)
+	return s.WriteResult(w, result)
 }
 
 func (s *CheckoutPoolServer) InitializeCheckoutHandler(w http.ResponseWriter, r *http.Request, id checkout.CheckoutId) error {
@@ -136,7 +136,7 @@ func (s *CheckoutPoolServer) InitializeCheckoutHandler(w http.ResponseWriter, r
 		return err
 	}
 
-	return s.WriteResult(w, result.Result)
+	return s.WriteResult(w, result)
 }
 
 func (s *CheckoutPoolServer) InventoryReservedHandler(w http.ResponseWriter, r *http.Request, id checkout.CheckoutId) error {
@@ -150,7 +150,7 @@ func (s *CheckoutPoolServer) InventoryReservedHandler(w http.ResponseWriter, r *
 		return err
 	}
 
-	return s.WriteResult(w, result.Result)
+	return s.WriteResult(w, result)
 }
 
 func (s *CheckoutPoolServer) OrderCreatedHandler(w http.ResponseWriter, r *http.Request, id checkout.CheckoutId) error {
@@ -164,7 +164,7 @@ func (s *CheckoutPoolServer) OrderCreatedHandler(w http.ResponseWriter, r *http.
 		return err
 	}
 
-	return s.WriteResult(w, result.Result)
+	return s.WriteResult(w, result)
 }
 
 func (s *CheckoutPoolServer) ConfirmationViewedHandler(w http.ResponseWriter, r *http.Request, id checkout.CheckoutId) error {
@@ -178,7 +178,7 @@ func (s *CheckoutPoolServer) ConfirmationViewedHandler(w http.ResponseWriter, r
 		return err
 	}
 
-	return s.WriteResult(w, result.Result)
+	return s.WriteResult(w, result)
 }
 
 func (s *CheckoutPoolServer) ContactDetailsUpdatedHandler(w http.ResponseWriter, r *http.Request, id checkout.CheckoutId) error {
@@ -192,7 +192,7 @@ func (s *CheckoutPoolServer) ContactDetailsUpdatedHandler(w http.ResponseWriter,
 		return err
 	}
 
-	return s.WriteResult(w, result.Result)
+	return s.WriteResult(w, result)
 }
 
 func (s *CheckoutPoolServer) StartCheckoutHandler(w http.ResponseWriter, r *http.Request) {
@@ -256,7 +256,7 @@ func (s *CheckoutPoolServer) StartCheckoutHandler(w http.ResponseWriter, r *http
 	// Set checkout cookie
 	setCheckoutCookie(w, checkoutId, r.TLS != nil)
 
-	if err := s.WriteResult(w, result.Result); err != nil {
+	if err := s.WriteResult(w, &result.Result); err != nil {
 		logger.Error("failed to write result", "error", err)
 	}
 }
@@ -299,7 +299,7 @@ func (s *CheckoutPoolServer) CreateOrUpdateCheckout(r *http.Request, grain *chec
 	}
 }
 
-func (s *CheckoutPoolServer) ApplyKlarnaPaymentStarted(ctx context.Context, klarnaOrder *CheckoutOrder, id checkout.CheckoutId) (*actor.MutationResult[*checkout.CheckoutGrain], error) {
+func (s *CheckoutPoolServer) ApplyKlarnaPaymentStarted(ctx context.Context, klarnaOrder *CheckoutOrder, id checkout.CheckoutId) (*actor.MutationResult[checkout.CheckoutGrain], error) {
 	method := "checkout"
 	return s.ApplyLocal(ctx, id, &messages.PaymentStarted{
 		PaymentId: klarnaOrder.ID,
@@ -329,28 +329,22 @@ func init() {
 	}
 }
 
-func (s *CheckoutPoolServer) applyAnywhere(ctx context.Context, id uint64, msgs ...proto.Message) error {
+func (s *CheckoutPoolServer) GetAnywhere(ctx context.Context, checkoutId cart.CartId) (*checkout.CheckoutGrain, error) {
-	host, found := s.OwnerHost(id)
+	id := uint64(checkoutId)
-	if !found {
+	if host, isOnOtherHost := s.OwnerHost(id); isOnOtherHost {
-		_, err := s.Apply(ctx, id, msgs...)
+		return host.Get(ctx, id)
-		return err
 	}
-	_, err := host.Apply(ctx, id, msgs...)
+	return s.Get(ctx, id)
-	return err
 }
 
-func (s *CheckoutPoolServer) getAnywhere(ctx context.Context, id uint64) (*checkout.CheckoutGrain, error) {
+func (s *CheckoutPoolServer) ApplyAnywhere(ctx context.Context, checkoutId cart.CartId, msgs ...proto.Message) error {
-	host, found := s.OwnerHost(id)
+	id := uint64(checkoutId)
-	if !found {
+	if host, isOnOtherHost := s.OwnerHost(id); isOnOtherHost {
-		grain, err := s.Get(ctx, id)
+		_, err := host.Apply(ctx, id, msgs...)
-		return grain, err
+		return err
 	}
-	ret := &checkout.CheckoutGrain{}
+	_, err := s.Apply(ctx, id, msgs...)
-	err := host.Get(ctx, id, ret)
+	return err
-	if err != nil {
-		return nil, err
-	}
-	return ret, nil
 }
 
 type StartPayment struct {

pkg/actor/base62-id.go

@@ -0,0 +1,131 @@
+package actor
+
+import (
+	"crypto/rand"
+	"encoding/json"
+	"fmt"
+)
+
+type GrainId uint64
+
+const base62Alphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+
+// Reverse lookup (0xFF marks invalid)
+var base62Rev [256]byte
+
+func init() {
+	for i := range base62Rev {
+		base62Rev[i] = 0xFF
+	}
+	for i := 0; i < len(base62Alphabet); i++ {
+		base62Rev[base62Alphabet[i]] = byte(i)
+	}
+}
+
+// String returns the canonical base62 encoding of the 64-bit id.
+func (id GrainId) String() string {
+	return encodeBase62(uint64(id))
+}
+
+// MarshalJSON encodes the cart id as a JSON string.
+func (id GrainId) MarshalJSON() ([]byte, error) {
+	return json.Marshal(id.String())
+}
+
+// UnmarshalJSON decodes a cart id from a JSON string containing base62 text.
+func (id *GrainId) UnmarshalJSON(data []byte) error {
+	var s string
+	if err := json.Unmarshal(data, &s); err != nil {
+		return err
+	}
+	parsed, ok := ParseGrainId(s)
+	if !ok {
+		return fmt.Errorf("invalid cart id: %q", s)
+	}
+	*id = parsed
+	return nil
+}
+
+// NewGrainId generates a new cryptographically random non-zero 64-bit id.
+func NewGrainId() (GrainId, error) {
+	var b [8]byte
+	if _, err := rand.Read(b[:]); err != nil {
+		return 0, fmt.Errorf("NewGrainId: %w", err)
+	}
+	u := (uint64(b[0]) << 56) |
+		(uint64(b[1]) << 48) |
+		(uint64(b[2]) << 40) |
+		(uint64(b[3]) << 32) |
+		(uint64(b[4]) << 24) |
+		(uint64(b[5]) << 16) |
+		(uint64(b[6]) << 8) |
+		uint64(b[7])
+	if u == 0 {
+		// Extremely unlikely; regenerate once to avoid "0" identifier if desired.
+		return NewGrainId()
+	}
+	return GrainId(u), nil
+}
+
+// MustNewGrainId panics if generation fails.
+func MustNewGrainId() GrainId {
+	id, err := NewGrainId()
+	if err != nil {
+		panic(err)
+	}
+	return id
+}
+
+// ParseGrainId parses a base62 string into a GrainId.
+// Returns (0,false) for invalid input.
+func ParseGrainId(s string) (GrainId, bool) {
+	// Accept length 1..11 (11 sufficient for 64 bits). Reject >11 immediately.
+	// Provide a slightly looser upper bound (<=16) only if you anticipate future
+	// extensions; here we stay strict.
+	if len(s) == 0 || len(s) > 11 {
+		return 0, false
+	}
+	u, ok := decodeBase62(s)
+	if !ok {
+		return 0, false
+	}
+	return GrainId(u), true
+}
+
+// MustParseGrainId panics on invalid base62 input.
+func MustParseGrainId(s string) GrainId {
+	id, ok := ParseGrainId(s)
+	if !ok {
+		panic(fmt.Sprintf("invalid cart id: %q", s))
+	}
+	return id
+}
+
+// encodeBase62 converts a uint64 to base62 (shortest form).
+func encodeBase62(u uint64) string {
+	if u == 0 {
+		return "0"
+	}
+	var buf [11]byte
+	i := len(buf)
+	for u > 0 {
+		i--
+		buf[i] = base62Alphabet[u%62]
+		u /= 62
+	}
+	return string(buf[i:])
+}
+
+// decodeBase62 converts base62 text to uint64.
+func decodeBase62(s string) (uint64, bool) {
+	var v uint64
+	for i := 0; i < len(s); i++ {
+		c := s[i]
+		d := base62Rev[c]
+		if d == 0xFF {
+			return 0, false
+		}
+		v = v*62 + uint64(d)
+	}
+	return v, true
+}

pkg/actor/grain_pool.go

@@ -15,29 +15,29 @@ type MutationResult[V any] struct {
 
 type GrainPool[V any] interface {
 	Apply(ctx context.Context, id uint64, mutation ...proto.Message) (*MutationResult[V], error)
-	Get(ctx context.Context, id uint64) (V, error)
+	Get(ctx context.Context, id uint64) (*V, error)
-	OwnerHost(id uint64) (Host, bool)
+	OwnerHost(id uint64) (Host[V], bool)
 	Hostname() string
 	TakeOwnership(id uint64)
 	HandleOwnershipChange(host string, ids []uint64) error
 	HandleRemoteExpiry(host string, ids []uint64) error
 	Negotiate(otherHosts []string)
 	GetLocalIds() []uint64
+	IsHealthy() bool
+	Close()
+	IsKnown(string) bool
 	RemoveHost(host string)
 	AddRemoteHost(host string)
-	IsHealthy() bool
-	IsKnown(string) bool
-	Close()
 }
 
 // Host abstracts a remote node capable of proxying cart requests.
-type Host interface {
+type Host[V any] interface {
 	AnnounceExpiry(ids []uint64)
 	Negotiate(otherHosts []string) ([]string, error)
 	Name() string
 	Proxy(id uint64, w http.ResponseWriter, r *http.Request, customBody io.Reader) (bool, error)
-	Apply(ctx context.Context, id uint64, mutation ...proto.Message) (bool, error)
+	Apply(ctx context.Context, id uint64, mutation ...proto.Message) (*MutationResult[V], error)
-	Get(ctx context.Context, id uint64, grain any) error
+	Get(ctx context.Context, id uint64) (*V, error)
 	GetActorIds() []uint64
 	Close() error
 	Ping() bool

pkg/actor/grpc_server.go

@@ -107,19 +107,27 @@ func (s *ControlServer[V]) AnnounceOwnership(ctx context.Context, req *messages.
 	}, nil
 }
 
+func toAny[V any](grain V) (*anypb.Any, error) {
+	data, err := json.Marshal(grain)
+	if err != nil {
+		return nil, err
+	}
+	return &anypb.Any{
+		Value: data,
+	}, nil
+}
+
 func (s *ControlServer[V]) Get(ctx context.Context, req *messages.GetRequest) (*messages.GetReply, error) {
 	grain, err := s.pool.Get(ctx, req.Id)
 	if err != nil {
 		return nil, err
 	}
-	data, err := json.Marshal(grain)
+	grainAny, err := toAny(grain)
 	if err != nil {
 		return nil, err
 	}
 	return &messages.GetReply{
-		Grain: &anypb.Any{
+		Grain: grainAny,
-			Value: data,
-		},
 	}, nil
 }
 
@@ -163,16 +171,40 @@ func (s *ControlServer[V]) Apply(ctx context.Context, in *messages.ApplyRequest)
 	for i, anyMsg := range in.Messages {
 		msg, err := anyMsg.UnmarshalNew()
 		if err != nil {
-			return &messages.ApplyResult{Accepted: false}, fmt.Errorf("failed to unmarshal message: %w", err)
+			return nil, fmt.Errorf("failed to unmarshal message: %w", err)
 		}
 		msgs[i] = msg
 	}
-	_, err := s.pool.Apply(ctx, in.Id, msgs...)
+	r, err := s.pool.Apply(ctx, in.Id, msgs...)
 	if err != nil {
-		return &messages.ApplyResult{Accepted: false}, err
+		return nil, err
+	}
+	grainAny, err := toAny(r)
+	if err != nil {
+		return nil, err
+	}
+	mutList := make([]*messages.MutationResult, len(in.Messages))
+	for i, msg := range r.Mutations {
+		mut, err := anypb.New(msg.Mutation)
+		if err != nil {
+			return nil, err
+		}
+		var errString *string
+		if msg.Error != nil {
+			s := msg.Error.Error()
+			errString = &s
+		}
+		mutList[i] = &messages.MutationResult{
+			Type:    msg.Type,
+			Message: mut,
+			Error:   errString,
+		}
 	}
 
-	return &messages.ApplyResult{Accepted: true}, nil
+	return &messages.ApplyResult{
+		State:     grainAny,
+		Mutations: mutList,
+	}, nil
 }
 
 // ControlPlane: Negotiate (merge host views)

pkg/actor/grpc_server_test.go

@@ -17,14 +17,14 @@ type mockGrainPool struct {
 	applied []proto.Message
 }
 
-func (m *mockGrainPool) Apply(ctx context.Context, id uint64, mutations ...proto.Message) (*MutationResult[*mockGrain], error) {
+func (m *mockGrainPool) Apply(ctx context.Context, id uint64, mutations ...proto.Message) (*MutationResult[mockGrain], error) {
 	m.applied = mutations
 	// Simulate successful application
-	return &MutationResult[*mockGrain]{
+	return &MutationResult[mockGrain]{
-		Result: &mockGrain{},
+		Result: mockGrain{},
 		Mutations: []ApplyResult{
-			{Error: nil}, // Assume success
+			{Type: "AddItem", Mutation: &cart_messages.AddItem{ItemId: 1, Quantity: 2}, Error: nil},
-			{Error: nil},
+			{Type: "RemoveItem", Mutation: &cart_messages.RemoveItem{Id: 1}, Error: nil},
 		},
 	}, nil
 }
@@ -33,7 +33,7 @@ func (m *mockGrainPool) Get(ctx context.Context, id uint64) (*mockGrain, error)
 	return &mockGrain{}, nil
 }
 
-func (m *mockGrainPool) OwnerHost(id uint64) (Host, bool) {
+func (m *mockGrainPool) OwnerHost(id uint64) (Host[mockGrain], bool) {
 	return nil, false
 }
 
@@ -58,7 +58,7 @@ func TestApplyRequestWithMutations(t *testing.T) {
 	pool := &mockGrainPool{}
 
 	// Create gRPC server
-	server, err := NewControlServer[*mockGrain](DefaultServerConfig(), pool)
+	server, err := NewControlServer[mockGrain](DefaultServerConfig(), pool)
 	if err != nil {
 		t.Fatalf("failed to create server: %v", err)
 	}
@@ -88,8 +88,16 @@ func TestApplyRequestWithMutations(t *testing.T) {
 	}
 
 	// Verify response
-	if !resp.Accepted {
+	if resp.State == nil {
-		t.Errorf("expected Accepted=true, got false")
+		t.Errorf("expected State to be non-nil")
+	}
+	if len(resp.Mutations) != 2 {
+		t.Errorf("expected 2 mutation results, got %d", len(resp.Mutations))
+	}
+	for i, mut := range resp.Mutations {
+		if mut.Error != nil {
+			t.Errorf("expected no error in mutation %d, got %s", i, *mut.Error)
+		}
 	}
 
 	// Verify mutations were extracted and applied
@@ -103,3 +111,40 @@ func TestApplyRequestWithMutations(t *testing.T) {
 		t.Errorf("expected RemoveItem with Id=1, got %v", pool.applied[1])
 	}
 }
+
+func TestGetRequest(t *testing.T) {
+	// Setup mock pool
+	pool := &mockGrainPool{}
+
+	// Create gRPC server
+	server, err := NewControlServer[mockGrain](DefaultServerConfig(), pool)
+	if err != nil {
+		t.Fatalf("failed to create server: %v", err)
+	}
+	defer server.GracefulStop()
+
+	// Create client connection
+	conn, err := grpc.Dial("localhost:1337", grpc.WithTransportCredentials(insecure.NewCredentials()))
+	if err != nil {
+		t.Fatalf("failed to dial: %v", err)
+	}
+	defer conn.Close()
+
+	client := control_plane_messages.NewControlPlaneClient(conn)
+
+	// Prepare GetRequest
+	req := &control_plane_messages.GetRequest{
+		Id: 123,
+	}
+
+	// Call Get
+	resp, err := client.Get(context.Background(), req)
+	if err != nil {
+		t.Fatalf("Get failed: %v", err)
+	}
+
+	// Verify response
+	if resp.Grain == nil {
+		t.Errorf("expected Grain to be non-nil")
+	}
+}

pkg/actor/simple_grain_pool.go

@@ -18,7 +18,7 @@ type SimpleGrainPool[V any] struct {
 	mutationRegistry MutationRegistry
 	spawn            func(ctx context.Context, id uint64) (Grain[V], error)
 	destroy          func(grain Grain[V]) error
-	spawnHost        func(host string) (Host, error)
+	spawnHost        func(host string) (Host[V], error)
 	listeners        []LogListener
 	storage          LogStorage[V]
 	ttl              time.Duration
@@ -27,8 +27,8 @@ type SimpleGrainPool[V any] struct {
 	// Cluster coordination --------------------------------------------------
 	hostname     string
 	remoteMu     sync.RWMutex
-	remoteOwners map[uint64]Host
+	remoteOwners map[uint64]Host[V]
-	remoteHosts  map[string]Host
+	remoteHosts  map[string]Host[V]
 	//discardedHostHandler *DiscardedHostHandler
 
 	// House-keeping ---------------------------------------------------------
@@ -38,7 +38,7 @@ type SimpleGrainPool[V any] struct {
 type GrainPoolConfig[V any] struct {
 	Hostname         string
 	Spawn            func(ctx context.Context, id uint64) (Grain[V], error)
-	SpawnHost        func(host string) (Host, error)
+	SpawnHost        func(host string) (Host[V], error)
 	Destroy          func(grain Grain[V]) error
 	TTL              time.Duration
 	PoolSize         int
@@ -57,8 +57,8 @@ func NewSimpleGrainPool[V any](config GrainPoolConfig[V]) (*SimpleGrainPool[V],
 		ttl:              config.TTL,
 		poolSize:         config.PoolSize,
 		hostname:         config.Hostname,
-		remoteOwners:     make(map[uint64]Host),
+		remoteOwners:     make(map[uint64]Host[V]),
-		remoteHosts:      make(map[string]Host),
+		remoteHosts:      make(map[string]Host[V]),
 	}
 
 	p.purgeTicker = time.NewTicker(time.Minute)
@@ -99,7 +99,7 @@ func (p *SimpleGrainPool[V]) purge() {
 		}
 	}
 	p.localMu.Unlock()
-	p.forAllHosts(func(remote Host) {
+	p.forAllHosts(func(remote Host[V]) {
 		remote.AnnounceExpiry(purgedIds)
 	})
 
@@ -136,7 +136,6 @@ func (p *SimpleGrainPool[V]) HandleRemoteExpiry(host string, ids []uint64) error
 }
 
 func (p *SimpleGrainPool[V]) HandleOwnershipChange(host string, ids []uint64) error {
-	log.Printf("host %s now owns %d cart ids", host, len(ids))
 	p.remoteMu.RLock()
 	remoteHost, exists := p.remoteHosts[host]
 	p.remoteMu.RUnlock()
@@ -168,7 +167,7 @@ func (p *SimpleGrainPool[V]) AddRemoteHost(host string) {
 	p.AddRemote(host)
 }
 
-func (p *SimpleGrainPool[V]) AddRemote(host string) (Host, error) {
+func (p *SimpleGrainPool[V]) AddRemote(host string) (Host[V], error) {
 	if host == "" {
 		return nil, fmt.Errorf("host is empty")
 	}
@@ -200,7 +199,7 @@ func (p *SimpleGrainPool[V]) AddRemote(host string) (Host, error) {
 	return remote, nil
 }
 
-func (p *SimpleGrainPool[V]) initializeRemote(remote Host) {
+func (p *SimpleGrainPool[V]) initializeRemote(remote Host[V]) {
 
 	remotesIds := remote.GetActorIds()
 
@@ -268,7 +267,7 @@ func (p *SimpleGrainPool[V]) IsKnown(host string) bool {
 	return ok
 }
 
-func (p *SimpleGrainPool[V]) pingLoop(remote Host) {
+func (p *SimpleGrainPool[V]) pingLoop(remote Host[V]) {
 	remote.Ping()
 	ticker := time.NewTicker(5 * time.Second)
 	defer ticker.Stop()
@@ -316,14 +315,14 @@ func (p *SimpleGrainPool[V]) SendNegotiation() {
 	p.remoteMu.RLock()
 	hosts := make([]string, 0, len(p.remoteHosts)+1)
 	hosts = append(hosts, p.hostname)
-	remotes := make([]Host, 0, len(p.remoteHosts))
+	remotes := make([]Host[V], 0, len(p.remoteHosts))
 	for h, r := range p.remoteHosts {
 		hosts = append(hosts, h)
 		remotes = append(remotes, r)
 	}
 	p.remoteMu.RUnlock()
 
-	p.forAllHosts(func(remote Host) {
+	p.forAllHosts(func(remote Host[V]) {
 		knownByRemote, err := remote.Negotiate(hosts)
 
 		if err != nil {
@@ -338,7 +337,7 @@ func (p *SimpleGrainPool[V]) SendNegotiation() {
 	})
 }
 
-func (p *SimpleGrainPool[V]) forAllHosts(fn func(Host)) {
+func (p *SimpleGrainPool[V]) forAllHosts(fn func(Host[V])) {
 	p.remoteMu.RLock()
 	rh := maps.Clone(p.remoteHosts)
 	p.remoteMu.RUnlock()
@@ -366,7 +365,7 @@ func (p *SimpleGrainPool[V]) broadcastOwnership(ids []uint64) {
 		return
 	}
 
-	p.forAllHosts(func(rh Host) {
+	p.forAllHosts(func(rh Host[V]) {
 		rh.AnnounceOwnership(p.hostname, ids)
 	})
 	log.Printf("%s taking ownership of %d ids", p.hostname, len(ids))
@@ -385,10 +384,11 @@ func (p *SimpleGrainPool[V]) getOrClaimGrain(ctx context.Context, id uint64) (Gr
 	if err != nil {
 		return nil, err
 	}
+	go p.broadcastOwnership([]uint64{id})
 	p.localMu.Lock()
 	p.grains[id] = grain
 	p.localMu.Unlock()
-	go p.broadcastOwnership([]uint64{id})
+
 	return grain, nil
 }
 
@@ -396,7 +396,7 @@ func (p *SimpleGrainPool[V]) getOrClaimGrain(ctx context.Context, id uint64) (Gr
 // var ErrNotOwner = fmt.Errorf("not owner")
 
 // Apply applies a mutation to a grain.
-func (p *SimpleGrainPool[V]) Apply(ctx context.Context, id uint64, mutation ...proto.Message) (*MutationResult[*V], error) {
+func (p *SimpleGrainPool[V]) Apply(ctx context.Context, id uint64, mutation ...proto.Message) (*MutationResult[V], error) {
 	grain, err := p.getOrClaimGrain(ctx, id)
 	if err != nil {
 		return nil, err
@@ -421,8 +421,8 @@ func (p *SimpleGrainPool[V]) Apply(ctx context.Context, id uint64, mutation ...p
 		return nil, err
 	}
 
-	return &MutationResult[*V]{
+	return &MutationResult[V]{
-		Result:    result,
+		Result:    *result,
 		Mutations: mutations,
 	}, nil
 }
@@ -437,7 +437,7 @@ func (p *SimpleGrainPool[V]) Get(ctx context.Context, id uint64) (*V, error) {
 }
 
 // OwnerHost reports the remote owner (if any) for the supplied cart id.
-func (p *SimpleGrainPool[V]) OwnerHost(id uint64) (Host, bool) {
+func (p *SimpleGrainPool[V]) OwnerHost(id uint64) (Host[V], bool) {
 	p.remoteMu.RLock()
 	defer p.remoteMu.RUnlock()
 	owner, ok := p.remoteOwners[id]
@@ -452,7 +452,7 @@ func (p *SimpleGrainPool[V]) Hostname() string {
 // Close notifies remotes that this host is shutting down.
 func (p *SimpleGrainPool[V]) Close() {
 
-	p.forAllHosts(func(rh Host) {
+	p.forAllHosts(func(rh Host[V]) {
 		rh.Close()
 	})
 

pkg/cart/cart-mutation-helper.go

@@ -23,9 +23,7 @@ func (c *CartMutationContext) ReserveItem(ctx context.Context, cartId CartId, sk
 	if quantity <= 0 || c.reservationService == nil {
 		return nil, nil
 	}
-	if sku != "919641" {
+
-		return nil, nil
-	}
 	l := inventory.LocationID("se")
 	if locationId != nil {
 		l = inventory.LocationID(*locationId)
@@ -49,6 +47,13 @@ func (c *CartMutationContext) ReserveItem(ctx context.Context, cartId CartId, sk
 
 }
 
+func (c *CartMutationContext) UseReservations(item *CartItem) bool {
+	if item.ReservationEndTime != nil {
+		return true
+	}
+	return item.Cgm == "55010"
+}
+
 func (c *CartMutationContext) ReleaseItem(ctx context.Context, cartId CartId, sku string, locationId *string) error {
 	if c.reservationService == nil {
 		return nil
@@ -60,12 +65,6 @@ func (c *CartMutationContext) ReleaseItem(ctx context.Context, cartId CartId, sk
 	return c.reservationService.ReleaseForCart(ctx, inventory.SKU(sku), l, inventory.CartID(cartId.String()))
 }
 
-func Create[T any]() func() *T {
-	return func() *T {
-		return new(T)
-	}
-}
-
 func NewCartMultationRegistry(context *CartMutationContext) actor.MutationRegistry {
 
 	reg := actor.NewMutationRegistry()

pkg/cart/cart_id.go

@@ -4,6 +4,8 @@ import (
 	"crypto/rand"
 	"encoding/json"
 	"fmt"
+
+	"git.k6n.net/go-cart-actor/pkg/actor"
 )
 
 // cart_id.go
@@ -34,7 +36,7 @@ import (
 //
 // ---------------------------------------------------------------------------
 
-type CartId uint64
+type CartId actor.GrainId
 
 const base62Alphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
 

pkg/cart/mutation_add_item.go

@@ -45,14 +45,16 @@ func (c *CartMutationContext) AddItem(g *CartGrain, m *cart_messages.AddItem) er
 		if !sameStore {
 			continue
 		}
-		if err := c.ReleaseItem(ctx, g.Id, existing.Sku, existing.StoreId); err != nil {
+		if c.UseReservations(existing) {
-			log.Printf("failed to release item %d: %v", existing.Id, err)
+			if err := c.ReleaseItem(ctx, g.Id, existing.Sku, existing.StoreId); err != nil {
+				log.Printf("failed to release item %d: %v", existing.Id, err)
+			}
+			endTime, err := c.ReserveItem(ctx, g.Id, existing.Sku, existing.StoreId, existing.Quantity+uint16(m.Quantity))
+			if err != nil {
+				return err
+			}
+			existing.ReservationEndTime = endTime
 		}
-		endTime, err := c.ReserveItem(ctx, g.Id, existing.Sku, existing.StoreId, existing.Quantity+uint16(m.Quantity))
-		if err != nil {
-			return err
-		}
-		existing.ReservationEndTime = endTime
 		existing.Quantity += uint16(m.Quantity)
 		existing.Stock = uint16(m.Stock)
 		// If existing had nil store but new has one, adopt it.
@@ -79,16 +81,6 @@ func (c *CartMutationContext) AddItem(g *CartGrain, m *cart_messages.AddItem) er
 		needsReservation = m.ReservationEndTime.AsTime().Before(time.Now())
 	}
 
-	if needsReservation {
-		endTime, err := c.ReserveItem(ctx, g.Id, m.Sku, m.StoreId, uint16(m.Quantity))
-		if err != nil {
-			return err
-		}
-		if endTime != nil {
-			m.ReservationEndTime = timestamppb.New(*endTime)
-		}
-	}
-
 	cartItem := &CartItem{
 		Id:       g.lastItemId,
 		ItemId:   uint32(m.ItemId),
@@ -123,10 +115,19 @@ func (c *CartMutationContext) AddItem(g *CartGrain, m *cart_messages.AddItem) er
 
 		StoreId: m.StoreId,
 	}
-	if m.ReservationEndTime != nil {
+
-		t := m.ReservationEndTime.AsTime()
+	if needsReservation && c.UseReservations(cartItem) {
-		cartItem.ReservationEndTime = &t
+		endTime, err := c.ReserveItem(ctx, g.Id, m.Sku, m.StoreId, uint16(m.Quantity))
+		if err != nil {
+			return err
+		}
+		if endTime != nil {
+			m.ReservationEndTime = timestamppb.New(*endTime)
+			t := m.ReservationEndTime.AsTime()
+			cartItem.ReservationEndTime = &t
+		}
 	}
+
 	g.Items = append(g.Items, cartItem)
 	g.UpdateTotals()
 	return nil

pkg/cart/mutation_change_quantity.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"log"
+	"time"
 
 	messages "git.k6n.net/go-cart-actor/proto/cart"
 )
@@ -49,9 +50,11 @@ func (c *CartMutationContext) ChangeQuantity(g *CartGrain, m *messages.ChangeQua
 	if m.Quantity <= 0 {
 		// Remove the item
 		itemToRemove := g.Items[foundIndex]
-		err := c.ReleaseItem(ctx, g.Id, itemToRemove.Sku, itemToRemove.StoreId)
+		if itemToRemove.ReservationEndTime != nil && itemToRemove.ReservationEndTime.Before(time.Now()) {
-		if err != nil {
+			err := c.ReleaseItem(ctx, g.Id, itemToRemove.Sku, itemToRemove.StoreId)
-			log.Printf("unable to release reservation for %s in location: %v", itemToRemove.Sku, itemToRemove.StoreId)
+			if err != nil {
+				log.Printf("unable to release reservation for %s in location: %v", itemToRemove.Sku, itemToRemove.StoreId)
+			}
 		}
 		g.Items = append(g.Items[:foundIndex], g.Items[foundIndex+1:]...)
 		g.UpdateTotals()
@@ -61,18 +64,20 @@ func (c *CartMutationContext) ChangeQuantity(g *CartGrain, m *messages.ChangeQua
 	if item == nil {
 		return fmt.Errorf("ChangeQuantity: item id %d not found", m.Id)
 	}
-	if item.ReservationEndTime != nil {
+	if c.UseReservations(item) {
-		err := c.ReleaseItem(ctx, g.Id, item.Sku, item.StoreId)
+		if item.ReservationEndTime != nil {
-		if err != nil {
+			err := c.ReleaseItem(ctx, g.Id, item.Sku, item.StoreId)
-			log.Printf("unable to release reservation for %s in location: %v", item.Sku, item.StoreId)
+			if err != nil {
-		}
+				log.Printf("unable to release reservation for %s in location: %v", item.Sku, item.StoreId)
+			}
 
+		}
+		endTime, err := c.ReserveItem(ctx, g.Id, item.Sku, item.StoreId, uint16(m.Quantity))
+		if err != nil {
+			return err
+		}
+		item.ReservationEndTime = endTime
 	}
-	endTime, err := c.ReserveItem(ctx, g.Id, item.Sku, item.StoreId, uint16(m.Quantity))
-	if err != nil {
-		return err
-	}
-	item.ReservationEndTime = endTime
 	item.Quantity = uint16(m.Quantity)
 	g.UpdateTotals()
 

pkg/discovery/types.go

@@ -9,3 +9,9 @@ type Discovery interface {
 	Discover() ([]string, error)
 	Watch() (<-chan HostChange, error)
 }
+
+type DiscoveryTarget interface {
+	IsKnown(string) bool
+	RemoveHost(host string)
+	AddRemoteHost(host string)
+}

pkg/proxy/remotehost.go

@@ -11,6 +11,7 @@ import (
 	"net/http"
 	"time"
 
+	"git.k6n.net/go-cart-actor/pkg/actor"
 	messages "git.k6n.net/go-cart-actor/proto/control"
 	"go.opentelemetry.io/contrib/bridges/otelslog"
 	"go.opentelemetry.io/otel"
@@ -130,25 +131,29 @@ func (h *RemoteHost[V]) Ping() bool {
 	return true
 }
 
-func (h *RemoteHost[V]) Get(ctx context.Context, id uint64, grain any) error {
+func (h *RemoteHost[V]) Get(ctx context.Context, id uint64) (*V, error) {
 	ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
 	defer cancel()
 	reply, error := h.controlClient.Get(ctx, &messages.GetRequest{Id: id})
 	if error != nil {
-		return error
+		return nil, error
 	}
-	return json.Unmarshal(reply.Grain.Value, grain)
+	var grain V
+	err := json.Unmarshal(reply.Grain.Value, &grain)
+	if err != nil {
+		return nil, fmt.Errorf("failed to unpack state: %w", err)
+	}
+	return &grain, nil
 }
 
-func (h *RemoteHost[V]) Apply(ctx context.Context, id uint64, mutation ...proto.Message) (bool, error) {
+func (h *RemoteHost[V]) Apply(ctx context.Context, id uint64, mutation ...proto.Message) (*actor.MutationResult[V], error) {
 	ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
 	defer cancel()
-
 	toSend := make([]*anypb.Any, len(mutation))
 	for i, msg := range mutation {
 		anyMsg, err := anypb.New(msg)
 		if err != nil {
-			return false, fmt.Errorf("failed to pack message: %w", err)
+			return nil, fmt.Errorf("failed to pack message: %w", err)
 		}
 		toSend[i] = anyMsg
 	}
@@ -160,10 +165,34 @@ func (h *RemoteHost[V]) Apply(ctx context.Context, id uint64, mutation ...proto.
 	if err != nil {
 		h.missedPings++
 		log.Printf("Apply %s failed: %v", h.host, err)
-		return false, err
+		return nil, err
 	}
 	h.missedPings = 0
-	return resp.Accepted, nil
+	var grain V
+	err = json.Unmarshal(resp.State.Value, &grain)
+	if err != nil {
+		return nil, fmt.Errorf("failed to unpack state: %w", err)
+	}
+	var mutationList []actor.ApplyResult
+	for _, msg := range resp.Mutations {
+
+		mutation, err := anypb.UnmarshalNew(msg.Message, proto.UnmarshalOptions{})
+		if err != nil {
+			return nil, fmt.Errorf("failed to unpack mutation: %w", err)
+		}
+		if msg.Error != nil {
+			err = errors.New(*msg.Error)
+		}
+		mutationList = append(mutationList, actor.ApplyResult{
+			Mutation: mutation,
+			Error:    err,
+		})
+	}
+	res := &actor.MutationResult[V]{
+		Result:    grain,
+		Mutations: mutationList,
+	}
+	return res, nil
 }
 
 func (h *RemoteHost[V]) Negotiate(knownHosts []string) ([]string, error) {

proto/control/control_plane.pb.go

@@ -592,16 +592,77 @@ func (x *GetReply) GetGrain() *anypb.Any {
 	return nil
 }
 
+type MutationResult struct {
+	state         protoimpl.MessageState `protogen:"open.v1"`
+	Type          string                 `protobuf:"bytes,1,opt,name=type,proto3" json:"type,omitempty"`
+	Message       *anypb.Any             `protobuf:"bytes,2,opt,name=message,proto3" json:"message,omitempty"`
+	Error         *string                `protobuf:"bytes,3,opt,name=error,proto3,oneof" json:"error,omitempty"`
+	unknownFields protoimpl.UnknownFields
+	sizeCache     protoimpl.SizeCache
+}
+
+func (x *MutationResult) Reset() {
+	*x = MutationResult{}
+	mi := &file_control_plane_proto_msgTypes[12]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *MutationResult) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*MutationResult) ProtoMessage() {}
+
+func (x *MutationResult) ProtoReflect() protoreflect.Message {
+	mi := &file_control_plane_proto_msgTypes[12]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use MutationResult.ProtoReflect.Descriptor instead.
+func (*MutationResult) Descriptor() ([]byte, []int) {
+	return file_control_plane_proto_rawDescGZIP(), []int{12}
+}
+
+func (x *MutationResult) GetType() string {
+	if x != nil {
+		return x.Type
+	}
+	return ""
+}
+
+func (x *MutationResult) GetMessage() *anypb.Any {
+	if x != nil {
+		return x.Message
+	}
+	return nil
+}
+
+func (x *MutationResult) GetError() string {
+	if x != nil && x.Error != nil {
+		return *x.Error
+	}
+	return ""
+}
+
 type ApplyResult struct {
 	state         protoimpl.MessageState `protogen:"open.v1"`
-	Accepted      bool                   `protobuf:"varint,1,opt,name=accepted,proto3" json:"accepted,omitempty"`
+	State         *anypb.Any             `protobuf:"bytes,1,opt,name=state,proto3" json:"state,omitempty"`
+	Mutations     []*MutationResult      `protobuf:"bytes,2,rep,name=mutations,proto3" json:"mutations,omitempty"`
 	unknownFields protoimpl.UnknownFields
 	sizeCache     protoimpl.SizeCache
 }
 
 func (x *ApplyResult) Reset() {
 	*x = ApplyResult{}
-	mi := &file_control_plane_proto_msgTypes[12]
+	mi := &file_control_plane_proto_msgTypes[13]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -613,7 +674,7 @@ func (x *ApplyResult) String() string {
 func (*ApplyResult) ProtoMessage() {}
 
 func (x *ApplyResult) ProtoReflect() protoreflect.Message {
-	mi := &file_control_plane_proto_msgTypes[12]
+	mi := &file_control_plane_proto_msgTypes[13]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -626,14 +687,21 @@ func (x *ApplyResult) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use ApplyResult.ProtoReflect.Descriptor instead.
 func (*ApplyResult) Descriptor() ([]byte, []int) {
-	return file_control_plane_proto_rawDescGZIP(), []int{12}
+	return file_control_plane_proto_rawDescGZIP(), []int{13}
 }
 
-func (x *ApplyResult) GetAccepted() bool {
+func (x *ApplyResult) GetState() *anypb.Any {
 	if x != nil {
-		return x.Accepted
+		return x.State
 	}
-	return false
+	return nil
+}
+
+func (x *ApplyResult) GetMutations() []*MutationResult {
+	if x != nil {
+		return x.Mutations
+	}
+	return nil
 }
 
 var File_control_plane_proto protoreflect.FileDescriptor
@@ -680,60 +748,73 @@ var file_control_plane_proto_rawDesc = string([]byte{
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+	0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
-	0x6f, 0x6e, 0x74, 0x72, 0x6f, 0x6c, 0x3b, 0x63, 0x6f, 0x6e, 0x74, 0x72, 0x6f, 0x6c, 0x5f, 0x70,
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-	0x72, 0x6f, 0x74, 0x6f, 0x33,
 })
 
 var (
@@ -748,7 +829,7 @@ func file_control_plane_proto_rawDescGZIP() []byte {
 	return file_control_plane_proto_rawDescData
 }
 
-var file_control_plane_proto_msgTypes = make([]protoimpl.MessageInfo, 13)
+var file_control_plane_proto_msgTypes = make([]protoimpl.MessageInfo, 14)
 var file_control_plane_proto_goTypes = []any{
 	(*Empty)(nil),             // 0: control_plane_messages.Empty
 	(*PingReply)(nil),         // 1: control_plane_messages.PingReply
@@ -762,33 +843,37 @@ var file_control_plane_proto_goTypes = []any{
 	(*ApplyRequest)(nil),      // 9: control_plane_messages.ApplyRequest
 	(*GetRequest)(nil),        // 10: control_plane_messages.GetRequest
 	(*GetReply)(nil),          // 11: control_plane_messages.GetReply
-	(*ApplyResult)(nil),       // 12: control_plane_messages.ApplyResult
+	(*MutationResult)(nil),    // 12: control_plane_messages.MutationResult
-	(*anypb.Any)(nil),         // 13: google.protobuf.Any
+	(*ApplyResult)(nil),       // 13: control_plane_messages.ApplyResult
+	(*anypb.Any)(nil),         // 14: google.protobuf.Any
 }
 var file_control_plane_proto_depIdxs = []int32{
-	13, // 0: control_plane_messages.ApplyRequest.messages:type_name -> google.protobuf.Any
+	14, // 0: control_plane_messages.ApplyRequest.messages:type_name -> google.protobuf.Any
-	13, // 1: control_plane_messages.GetReply.grain:type_name -> google.protobuf.Any
+	14, // 1: control_plane_messages.GetReply.grain:type_name -> google.protobuf.Any
-	0,  // 2: control_plane_messages.ControlPlane.Ping:input_type -> control_plane_messages.Empty
+	14, // 2: control_plane_messages.MutationResult.message:type_name -> google.protobuf.Any
-	2,  // 3: control_plane_messages.ControlPlane.Negotiate:input_type -> control_plane_messages.NegotiateRequest
+	14, // 3: control_plane_messages.ApplyResult.state:type_name -> google.protobuf.Any
-	0,  // 4: control_plane_messages.ControlPlane.GetLocalActorIds:input_type -> control_plane_messages.Empty
+	12, // 4: control_plane_messages.ApplyResult.mutations:type_name -> control_plane_messages.MutationResult
-	7,  // 5: control_plane_messages.ControlPlane.AnnounceOwnership:input_type -> control_plane_messages.OwnershipAnnounce
+	0,  // 5: control_plane_messages.ControlPlane.Ping:input_type -> control_plane_messages.Empty
-	9,  // 6: control_plane_messages.ControlPlane.Apply:input_type -> control_plane_messages.ApplyRequest
+	2,  // 6: control_plane_messages.ControlPlane.Negotiate:input_type -> control_plane_messages.NegotiateRequest
-	8,  // 7: control_plane_messages.ControlPlane.AnnounceExpiry:input_type -> control_plane_messages.ExpiryAnnounce
+	0,  // 7: control_plane_messages.ControlPlane.GetLocalActorIds:input_type -> control_plane_messages.Empty
-	6,  // 8: control_plane_messages.ControlPlane.Closing:input_type -> control_plane_messages.ClosingNotice
+	7,  // 8: control_plane_messages.ControlPlane.AnnounceOwnership:input_type -> control_plane_messages.OwnershipAnnounce
-	10, // 9: control_plane_messages.ControlPlane.Get:input_type -> control_plane_messages.GetRequest
+	9,  // 9: control_plane_messages.ControlPlane.Apply:input_type -> control_plane_messages.ApplyRequest
-	1,  // 10: control_plane_messages.ControlPlane.Ping:output_type -> control_plane_messages.PingReply
+	8,  // 10: control_plane_messages.ControlPlane.AnnounceExpiry:input_type -> control_plane_messages.ExpiryAnnounce
-	3,  // 11: control_plane_messages.ControlPlane.Negotiate:output_type -> control_plane_messages.NegotiateReply
+	6,  // 11: control_plane_messages.ControlPlane.Closing:input_type -> control_plane_messages.ClosingNotice
-	4,  // 12: control_plane_messages.ControlPlane.GetLocalActorIds:output_type -> control_plane_messages.ActorIdsReply
+	10, // 12: control_plane_messages.ControlPlane.Get:input_type -> control_plane_messages.GetRequest
-	5,  // 13: control_plane_messages.ControlPlane.AnnounceOwnership:output_type -> control_plane_messages.OwnerChangeAck
+	1,  // 13: control_plane_messages.ControlPlane.Ping:output_type -> control_plane_messages.PingReply
-	12, // 14: control_plane_messages.ControlPlane.Apply:output_type -> control_plane_messages.ApplyResult
+	3,  // 14: control_plane_messages.ControlPlane.Negotiate:output_type -> control_plane_messages.NegotiateReply
-	5,  // 15: control_plane_messages.ControlPlane.AnnounceExpiry:output_type -> control_plane_messages.OwnerChangeAck
+	4,  // 15: control_plane_messages.ControlPlane.GetLocalActorIds:output_type -> control_plane_messages.ActorIdsReply
-	5,  // 16: control_plane_messages.ControlPlane.Closing:output_type -> control_plane_messages.OwnerChangeAck
+	5,  // 16: control_plane_messages.ControlPlane.AnnounceOwnership:output_type -> control_plane_messages.OwnerChangeAck
-	11, // 17: control_plane_messages.ControlPlane.Get:output_type -> control_plane_messages.GetReply
+	13, // 17: control_plane_messages.ControlPlane.Apply:output_type -> control_plane_messages.ApplyResult
-	10, // [10:18] is the sub-list for method output_type
+	5,  // 18: control_plane_messages.ControlPlane.AnnounceExpiry:output_type -> control_plane_messages.OwnerChangeAck
-	2,  // [2:10] is the sub-list for method input_type
+	5,  // 19: control_plane_messages.ControlPlane.Closing:output_type -> control_plane_messages.OwnerChangeAck
-	2,  // [2:2] is the sub-list for extension type_name
+	11, // 20: control_plane_messages.ControlPlane.Get:output_type -> control_plane_messages.GetReply
-	2,  // [2:2] is the sub-list for extension extendee
+	13, // [13:21] is the sub-list for method output_type
-	0,  // [0:2] is the sub-list for field type_name
+	5,  // [5:13] is the sub-list for method input_type
+	5,  // [5:5] is the sub-list for extension type_name
+	5,  // [5:5] is the sub-list for extension extendee
+	0,  // [0:5] is the sub-list for field type_name
 }
 
 func init() { file_control_plane_proto_init() }
@@ -796,13 +881,14 @@ func file_control_plane_proto_init() {
 	if File_control_plane_proto != nil {
 		return
 	}
+	file_control_plane_proto_msgTypes[12].OneofWrappers = []any{}
 	type x struct{}
 	out := protoimpl.TypeBuilder{
 		File: protoimpl.DescBuilder{
 			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
 			RawDescriptor: unsafe.Slice(unsafe.StringData(file_control_plane_proto_rawDesc), len(file_control_plane_proto_rawDesc)),
 			NumEnums:      0,
-			NumMessages:   13,
+			NumMessages:   14,
 			NumExtensions: 0,
 			NumServices:   1,
 		},

proto/control_plane.proto

@@ -81,8 +81,15 @@ message GetReply {
     google.protobuf.Any grain = 1;
 }
 
+message MutationResult {
+    string type = 1;
+    google.protobuf.Any message = 2;
+    optional string error = 3;
+}
+
 message ApplyResult {
-  bool accepted = 1;
+    google.protobuf.Any state = 1;
+    repeated MutationResult mutations = 2;
 }
 
 // ControlPlane defines cluster coordination and ownership operations.