[client] Refactor lastNetworkMapSerial handling in GrpcClient

- Removed atomic operations for lastNetworkMapSerial and replaced them with mutex-based methods for thread-safe access.

shared/management/client/grpc.go

@@ -6,7 +6,6 @@ import (
 	"fmt"
 	"io"
 	"sync"
-	"sync/atomic"
 	"time"
 
 	"google.golang.org/grpc/codes"
@@ -46,7 +45,8 @@ type GrpcClient struct {
 	connStateCallback     ConnStateNotifier
 	connStateCallbackLock sync.RWMutex
 	// lastNetworkMapSerial stores last seen network map serial to optimize sync
-	lastNetworkMapSerial uint64
+	lastNetworkMapSerial   uint64
+	lastNetworkMapSerialMu sync.Mutex
 }
 
 // NewClient creates a new client to Management service
@@ -220,7 +220,7 @@ func (c *GrpcClient) GetNetworkMap(sysInfo *system.Info) (*proto.NetworkMap, err
 	}
 
 	// update last seen serial
-	atomic.StoreUint64(&c.lastNetworkMapSerial, decryptedResp.GetNetworkMap().GetSerial())
+	c.setLastNetworkMapSerial(decryptedResp.GetNetworkMap().GetSerial())
 
 	return decryptedResp.GetNetworkMap(), nil
 }
@@ -235,7 +235,7 @@ func (c *GrpcClient) connectToStream(ctx context.Context, serverPubKey wgtypes.K
 			recomputed.Files = sysInfo.Files
 		}
 	}
-	req := &proto.SyncRequest{Meta: infoToMetaData(recomputed), NetworkMapSerial: atomic.LoadUint64(&c.lastNetworkMapSerial)}
+	req := &proto.SyncRequest{Meta: infoToMetaData(recomputed), NetworkMapSerial: c.getLastNetworkMapSerial()}
 
 	myPrivateKey := c.key
 	myPublicKey := myPrivateKey.PublicKey()
@@ -275,7 +275,7 @@ func (c *GrpcClient) receiveEvents(stream proto.ManagementService_SyncClient, se
 
 		// track latest network map serial if present
 		if decryptedResp.GetNetworkMap() != nil {
-			atomic.StoreUint64(&c.lastNetworkMapSerial, decryptedResp.GetNetworkMap().GetSerial())
+			c.setLastNetworkMapSerial(decryptedResp.GetNetworkMap().GetSerial())
 		}
 
 		if err := msgHandler(decryptedResp); err != nil {
@@ -602,3 +602,18 @@ func infoToMetaData(info *system.Info) *proto.PeerSystemMeta {
 		},
 	}
 }
+
+// setLastNetworkMapSerial updates the cached last seen network map serial in a 32-bit safe manner
+func (c *GrpcClient) setLastNetworkMapSerial(serial uint64) {
+	c.lastNetworkMapSerialMu.Lock()
+	c.lastNetworkMapSerial = serial
+	c.lastNetworkMapSerialMu.Unlock()
+}
+
+// getLastNetworkMapSerial returns the cached last seen network map serial in a 32-bit safe manner
+func (c *GrpcClient) getLastNetworkMapSerial() uint64 {
+	c.lastNetworkMapSerialMu.Lock()
+	v := c.lastNetworkMapSerial
+	c.lastNetworkMapSerialMu.Unlock()
+	return v
+}