MM-52600: [Shared Channels] Shared channels do not sync channel membership (#30976)

server/channels/app/channel.go

@@ -1711,6 +1711,13 @@ func (a *App) addUserToChannel(c request.CTX, user *model.User, channel *model.C
 	a.Srv().Platform().InvalidateChannelCacheForUser(user.Id)
 	a.invalidateCacheForChannelMembers(channel.Id)
 
+	// Synchronize membership change for shared channels
+	if channel.IsShared() {
+		if scs := a.Srv().Platform().GetSharedChannelService(); scs != nil {
+			scs.HandleMembershipChange(channel.Id, user.Id, true, user.GetRemoteID())
+		}
+	}
+
 	return newMember, nil
 }
 
@@ -2236,7 +2243,12 @@ func (s *Server) getChannelMemberLastViewedAt(c request.CTX, channelID string, u
 }
 
 func (a *App) GetChannelMembersPage(c request.CTX, channelID string, page, perPage int) (model.ChannelMembers, *model.AppError) {
-	channelMembers, err := a.Srv().Store().Channel().GetMembers(channelID, page*perPage, perPage)
+	opts := model.ChannelMembersGetOptions{
+		ChannelID: channelID,
+		Offset:    page * perPage,
+		Limit:     perPage,
+	}
+	channelMembers, err := a.Srv().Store().Channel().GetMembers(opts)
 	if err != nil {
 		return nil, model.NewAppError("GetChannelMembersPage", "app.channel.get_members.app_error", nil, "", http.StatusInternalServerError).Wrap(err)
 	}
@@ -2740,6 +2752,14 @@ func (a *App) removeUserFromChannel(c request.CTX, userIDToRemove string, remove
 	userMsg.Add("remover_id", removerUserId)
 	a.Publish(userMsg)
 
+	// Synchronize membership change for shared channels
+	if channel.IsShared() {
+		// isAdd=false, empty remoteId means locally initiated
+		if scs := a.Srv().Platform().GetSharedChannelService(); scs != nil {
+			scs.HandleMembershipChange(channel.Id, userIDToRemove, false, "")
+		}
+	}
+
 	return nil
 }
 
@@ -3639,7 +3659,12 @@ func (a *App) forEachChannelMember(c request.CTX, channelID string, f func(model
 	page := 0
 
 	for {
-		channelMembers, err := a.Srv().Store().Channel().GetMembers(channelID, page*perPage, perPage)
+		opts := model.ChannelMembersGetOptions{
+			ChannelID: channelID,
+			Offset:    page * perPage,
+			Limit:     perPage,
+		}
+		channelMembers, err := a.Srv().Store().Channel().GetMembers(opts)
 		if err != nil {
 			return err
 		}

server/channels/app/channel_test.go

@@ -2513,8 +2513,16 @@ func TestClearChannelMembersCache(t *testing.T) {
 			ChannelId: "1",
 		})
 	}
-	mockChannelStore.On("GetMembers", "channelID", 0, 100).Return(cms, nil)
-	mockChannelStore.On("GetMembers", "channelID", 100, 100).Return(model.ChannelMembers{
+	mockChannelStore.On("GetMembers", model.ChannelMembersGetOptions{
+		ChannelID: "channelID",
+		Offset:    0,
+		Limit:     100,
+	}).Return(cms, nil)
+	mockChannelStore.On("GetMembers", model.ChannelMembersGetOptions{
+		ChannelID: "channelID",
+		Offset:    100,
+		Limit:     100,
+	}).Return(model.ChannelMembers{
 		model.ChannelMember{
 			ChannelId: "1",
 		},

server/channels/app/platform/shared_channel_service_iface.go

@@ -23,6 +23,7 @@ type SharedChannelServiceIFace interface {
 	CheckChannelNotShared(channelID string) error
 	CheckChannelIsShared(channelID string) error
 	CheckCanInviteToSharedChannel(channelId string) error
+	HandleMembershipChange(channelID, userID string, isAdd bool, remoteID string)
 }
 
 type MockOptionSharedChannelService func(service *mockSharedChannelService)
@@ -77,3 +78,7 @@ func (mrcs *mockSharedChannelService) SendChannelInvite(channel *model.Channel,
 func (mrcs *mockSharedChannelService) NumInvitations() int {
 	return mrcs.numInvitations
 }
+
+func (mrcs *mockSharedChannelService) HandleMembershipChange(channelID, userID string, isAdd bool, remoteID string) {
+	// This is a mock implementation - it doesn't need to do anything
+}

server/channels/app/shared_channel_service_iface.go

@@ -26,6 +26,7 @@ type SharedChannelServiceIFace interface {
 	CheckChannelNotShared(channelID string) error
 	CheckChannelIsShared(channelID string) error
 	CheckCanInviteToSharedChannel(channelId string) error
+	HandleMembershipChange(channelID, userID string, isAdd bool, remoteID string)
 }
 
 func NewMockSharedChannelService(service SharedChannelServiceIFace) *mockSharedChannelService {
@@ -91,3 +92,9 @@ func (mrcs *mockSharedChannelService) SendChannelInvite(channel *model.Channel,
 func (mrcs *mockSharedChannelService) NumInvitations() int {
 	return mrcs.numInvitations
 }
+
+func (mrcs *mockSharedChannelService) HandleMembershipChange(channelID, userID string, isAdd bool, remoteID string) {
+	if mrcs.SharedChannelServiceIFace != nil {
+		mrcs.SharedChannelServiceIFace.HandleMembershipChange(channelID, userID, isAdd, remoteID)
+	}
+}

server/channels/app/shared_channel_sync_self_referential_utils_test.go

@@ -105,6 +105,27 @@ func (h *SelfReferentialSyncHandler) HandleRequest(w http.ResponseWriter, r *htt
 						}
 					}
 
+					// Handle membership sync using unified field
+					if len(syncMsg.MembershipChanges) > 0 {
+						batch := make([]string, 0)
+						for _, change := range syncMsg.MembershipChanges {
+							if change.IsAdd {
+								syncResp.UsersSyncd = append(syncResp.UsersSyncd, change.UserId)
+								batch = append(batch, change.UserId)
+							}
+						}
+
+						// Call appropriate callback
+						if len(batch) > 0 {
+							if h.OnBatchSync != nil {
+								h.OnBatchSync(batch, currentCall)
+							}
+							if len(batch) == 1 && h.OnIndividualSync != nil {
+								h.OnIndividualSync(batch[0], currentCall)
+							}
+						}
+					}
+
 					_ = response.SetPayload(syncResp)
 				}
 			}
@@ -135,28 +156,36 @@ func (h *SelfReferentialSyncHandler) GetSyncMessageCount() int32 {
 	return atomic.LoadInt32(h.syncMessageCount)
 }
 
-// GetUsersFromSyncMsg extracts user IDs from a sync message
-func GetUsersFromSyncMsg(msg model.SyncMsg) []string {
-	var userIds []string
-
-	// Extract from users field
-	for userId := range msg.Users {
-		userIds = append(userIds, userId)
-	}
-
-	return userIds
-}
-
 // EnsureCleanState ensures a clean test state by removing all shared channels, remote clusters,
 // and extra team/channel members. This helps prevent state pollution between tests.
 func EnsureCleanState(t *testing.T, th *TestHelper, ss store.Store) {
 	t.Helper()
 
+	// First, wait for any pending async tasks to complete, then shutdown services
+	scsInterface := th.App.Srv().GetSharedChannelSyncService()
+	if scsInterface != nil && scsInterface.Active() {
+		// Cast to concrete type to access testing methods
+		if service, ok := scsInterface.(*sharedchannel.Service); ok {
+			// Wait for any pending tasks from previous tests to complete
+			require.Eventually(t, func() bool {
+				return !service.HasPendingTasksForTesting()
+			}, 10*time.Second, 100*time.Millisecond, "All pending sync tasks should complete before cleanup")
+		}
+
+		// Shutdown the shared channel service to stop any async operations
+		_ = scsInterface.Shutdown()
+
+		// Wait for shutdown to complete with more time
+		require.Eventually(t, func() bool {
+			return !scsInterface.Active()
+		}, 5*time.Second, 100*time.Millisecond, "Shared channel service should be inactive after shutdown")
+	}
+
 	// Clear all shared channels and remotes from previous tests
 	allSharedChannels, _ := ss.SharedChannel().GetAll(0, 1000, model.SharedChannelFilterOpts{})
 	for _, sc := range allSharedChannels {
 		// Delete all remotes for this channel
-		remotes, _ := ss.SharedChannel().GetRemotes(0, 100, model.SharedChannelRemoteFilterOpts{ChannelId: sc.ChannelId})
+		remotes, _ := ss.SharedChannel().GetRemotes(0, 999999, model.SharedChannelRemoteFilterOpts{ChannelId: sc.ChannelId})
 		for _, remote := range remotes {
 			_, _ = ss.SharedChannel().DeleteRemote(remote.Id)
 		}
@@ -170,13 +199,32 @@ func EnsureCleanState(t *testing.T, th *TestHelper, ss store.Store) {
 		_, _ = ss.RemoteCluster().Delete(rc.RemoteId)
 	}
 
+	// Clear all SharedChannelUsers sync state - this is critical for test isolation
+	// The SharedChannelUsers table tracks per-user sync timestamps that can interfere between tests
+	_, _ = th.SQLStore.GetMaster().Exec("DELETE FROM SharedChannelUsers WHERE 1=1")
+
+	// Clear all SharedChannelAttachments sync state
+	_, _ = th.SQLStore.GetMaster().Exec("DELETE FROM SharedChannelAttachments WHERE 1=1")
+
+	// Reset sync cursors in any remaining SharedChannelRemotes (before they get deleted)
+	// This ensures cursors don't persist if deletion fails
+	_, _ = th.SQLStore.GetMaster().Exec(`UPDATE SharedChannelRemotes SET 
+		LastPostCreateAt = 0, 
+		LastPostCreateId = '', 
+		LastPostUpdateAt = 0, 
+		LastPostId = '', 
+		LastMembersSyncAt = 0 
+		WHERE 1=1`)
+
 	// Remove all channel members from test channels (except the basic team/channel setup)
 	channels, _ := ss.Channel().GetAll(th.BasicTeam.Id)
 	for _, channel := range channels {
 		// Skip direct message and group channels, and skip the default channels
 		if channel.Type != model.ChannelTypeDirect && channel.Type != model.ChannelTypeGroup &&
 			channel.Id != th.BasicChannel.Id {
-			members, _ := ss.Channel().GetMembers(channel.Id, 0, 10000)
+			members, _ := ss.Channel().GetMembers(model.ChannelMembersGetOptions{
+				ChannelID: channel.Id,
+			})
 			for _, member := range members {
 				_ = ss.Channel().RemoveMember(th.Context, channel.Id, member.UserId)
 			}
@@ -228,12 +276,16 @@ func EnsureCleanState(t *testing.T, th *TestHelper, ss store.Store) {
 		cfg.ConnectedWorkspacesSettings.GlobalUserSyncBatchSize = &defaultBatchSize
 	})
 
-	// Ensure services are running and ready
-	scsInterface := th.App.Srv().GetSharedChannelSyncService()
-	if scs, ok := scsInterface.(*sharedchannel.Service); ok {
-		require.Eventually(t, func() bool {
-			return scs.Active()
-		}, 2*time.Second, 100*time.Millisecond, "Shared channel service should be active")
+	// Restart services and ensure they are running and ready
+	if scsInterface != nil {
+		// Restart the shared channel service
+		_ = scsInterface.Start()
+
+		if scs, ok := scsInterface.(*sharedchannel.Service); ok {
+			require.Eventually(t, func() bool {
+				return scs.Active()
+			}, 5*time.Second, 100*time.Millisecond, "Shared channel service should be active after restart")
+		}
 	}
 
 	rcService := th.App.Srv().GetRemoteClusterService()
@@ -243,6 +295,6 @@ func EnsureCleanState(t *testing.T, th *TestHelper, ss store.Store) {
 		}
 		require.Eventually(t, func() bool {
 			return rcService.Active()
-		}, 2*time.Second, 100*time.Millisecond, "Remote cluster service should be active")
+		}, 5*time.Second, 100*time.Millisecond, "Remote cluster service should be active")
 	}
 }

server/channels/app/shared_channel_test.go

@@ -16,6 +16,7 @@ func setupSharedChannels(tb testing.TB) *TestHelper {
 	return SetupConfig(tb, func(cfg *model.Config) {
 		*cfg.ConnectedWorkspacesSettings.EnableRemoteClusterService = true
 		*cfg.ConnectedWorkspacesSettings.EnableSharedChannels = true
+		cfg.FeatureFlags.EnableSharedChannelsMemberSync = true
 	})
 }
 

server/channels/db/migrations/migrations.list

@@ -275,6 +275,8 @@ channels/db/migrations/mysql/000138_add_default_category_name_to_channel.down.sq
 channels/db/migrations/mysql/000138_add_default_category_name_to_channel.up.sql
 channels/db/migrations/mysql/000139_remoteclusters_add_last_global_user_sync_at.down.sql
 channels/db/migrations/mysql/000139_remoteclusters_add_last_global_user_sync_at.up.sql
+channels/db/migrations/mysql/000140_add_lastmemberssyncat_to_sharedchannelremotes.down.sql
+channels/db/migrations/mysql/000140_add_lastmemberssyncat_to_sharedchannelremotes.up.sql
 channels/db/migrations/postgres/000001_create_teams.down.sql
 channels/db/migrations/postgres/000001_create_teams.up.sql
 channels/db/migrations/postgres/000002_create_team_members.down.sql
@@ -551,3 +553,5 @@ channels/db/migrations/postgres/000138_add_default_category_name_to_channel.down
 channels/db/migrations/postgres/000138_add_default_category_name_to_channel.up.sql
 channels/db/migrations/postgres/000139_remoteclusters_add_last_global_user_sync_at.down.sql
 channels/db/migrations/postgres/000139_remoteclusters_add_last_global_user_sync_at.up.sql
+channels/db/migrations/postgres/000140_add_lastmemberssyncat_to_sharedchannelremotes.down.sql
+channels/db/migrations/postgres/000140_add_lastmemberssyncat_to_sharedchannelremotes.up.sql

server/channels/db/migrations/mysql/000140_add_lastmemberssyncat_to_sharedchannelremotes.down.sql

@@ -0,0 +1,29 @@
+SET @preparedStatement = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS
+        WHERE table_name = 'SharedChannelRemotes'
+        AND table_schema = DATABASE()
+        AND column_name = 'LastMembersSyncAt'
+    ) > 0,
+    'ALTER TABLE SharedChannelRemotes DROP COLUMN LastMembersSyncAt;',
+    'SELECT 1'
+));
+
+PREPARE alterIfExists FROM @preparedStatement;
+EXECUTE alterIfExists;
+DEALLOCATE PREPARE alterIfExists;
+
+SET @preparedStatement2 = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS
+        WHERE table_name = 'SharedChannelUsers'
+        AND table_schema = DATABASE()
+        AND column_name = 'LastMembershipSyncAt'
+    ) > 0,
+    'ALTER TABLE SharedChannelUsers DROP COLUMN LastMembershipSyncAt;',
+    'SELECT 1'
+));
+
+PREPARE alterIfExists2 FROM @preparedStatement2;
+EXECUTE alterIfExists2;
+DEALLOCATE PREPARE alterIfExists2;

server/channels/db/migrations/mysql/000140_add_lastmemberssyncat_to_sharedchannelremotes.up.sql

@@ -0,0 +1,29 @@
+SET @preparedStatement = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS
+        WHERE table_name = 'SharedChannelRemotes'
+        AND table_schema = DATABASE()
+        AND column_name = 'LastMembersSyncAt'
+    ) > 0,
+    'SELECT 1',
+    'ALTER TABLE SharedChannelRemotes ADD LastMembersSyncAt bigint DEFAULT 0;'
+));
+
+PREPARE alterIfNotExists FROM @preparedStatement;
+EXECUTE alterIfNotExists;
+DEALLOCATE PREPARE alterIfNotExists;
+
+SET @preparedStatement2 = (SELECT IF(
+    (
+        SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS
+        WHERE table_name = 'SharedChannelUsers'
+        AND table_schema = DATABASE()
+        AND column_name = 'LastMembershipSyncAt'
+    ) > 0,
+    'SELECT 1',
+    'ALTER TABLE SharedChannelUsers ADD LastMembershipSyncAt bigint DEFAULT 0;'
+));
+
+PREPARE alterIfNotExists2 FROM @preparedStatement2;
+EXECUTE alterIfNotExists2;
+DEALLOCATE PREPARE alterIfNotExists2;

server/channels/db/migrations/postgres/000140_add_lastmemberssyncat_to_sharedchannelremotes.down.sql

@@ -0,0 +1,2 @@
+ALTER TABLE sharedchannelremotes DROP COLUMN IF EXISTS lastmemberssyncat;
+ALTER TABLE sharedchannelusers DROP COLUMN IF EXISTS lastmembershipsyncat;

server/channels/db/migrations/postgres/000140_add_lastmemberssyncat_to_sharedchannelremotes.up.sql

@@ -0,0 +1,2 @@
+ALTER TABLE sharedchannelremotes ADD COLUMN IF NOT EXISTS lastmemberssyncat bigint DEFAULT 0;
+ALTER TABLE sharedchannelusers ADD COLUMN IF NOT EXISTS lastmembershipsyncat bigint DEFAULT 0;

server/channels/store/retrylayer/retrylayer.go

@@ -2081,11 +2081,11 @@ func (s *RetryLayerChannelStore) GetMemberLastViewedAt(ctx context.Context, chan
 
 }
 
-func (s *RetryLayerChannelStore) GetMembers(channelID string, offset int, limit int) (model.ChannelMembers, error) {
+func (s *RetryLayerChannelStore) GetMembers(opts model.ChannelMembersGetOptions) (model.ChannelMembers, error) {
 
 	tries := 0
 	for {
-		result, err := s.ChannelStore.GetMembers(channelID, offset, limit)
+		result, err := s.ChannelStore.GetMembers(opts)
 		if err == nil {
 			return result, nil
 		}
@@ -11642,6 +11642,27 @@ func (s *RetryLayerSharedChannelStore) GetSingleUser(userID string, channelID st
 
 }
 
+func (s *RetryLayerSharedChannelStore) GetUserChanges(userID string, channelID string, afterTime int64) ([]*model.SharedChannelUser, error) {
+
+	tries := 0
+	for {
+		result, err := s.SharedChannelStore.GetUserChanges(userID, channelID, afterTime)
+		if err == nil {
+			return result, nil
+		}
+		if !isRepeatableError(err) {
+			return result, err
+		}
+		tries++
+		if tries >= 3 {
+			err = errors.Wrap(err, "giving up after 3 consecutive repeatable transaction failures")
+			return result, err
+		}
+		timepkg.Sleep(100 * timepkg.Millisecond)
+	}
+
+}
+
 func (s *RetryLayerSharedChannelStore) GetUsersForSync(filter model.GetUsersForSyncFilter) ([]*model.User, error) {
 
 	tries := 0
@@ -11894,6 +11915,48 @@ func (s *RetryLayerSharedChannelStore) UpdateRemoteCursor(id string, cursor mode
 
 }
 
+func (s *RetryLayerSharedChannelStore) UpdateRemoteMembershipCursor(id string, syncTime int64) error {
+
+	tries := 0
+	for {
+		err := s.SharedChannelStore.UpdateRemoteMembershipCursor(id, syncTime)
+		if err == nil {
+			return nil
+		}
+		if !isRepeatableError(err) {
+			return err
+		}
+		tries++
+		if tries >= 3 {
+			err = errors.Wrap(err, "giving up after 3 consecutive repeatable transaction failures")
+			return err
+		}
+		timepkg.Sleep(100 * timepkg.Millisecond)
+	}
+
+}
+
+func (s *RetryLayerSharedChannelStore) UpdateUserLastMembershipSyncAt(userID string, channelID string, remoteID string, syncTime int64) error {
+
+	tries := 0
+	for {
+		err := s.SharedChannelStore.UpdateUserLastMembershipSyncAt(userID, channelID, remoteID, syncTime)
+		if err == nil {
+			return nil
+		}
+		if !isRepeatableError(err) {
+			return err
+		}
+		tries++
+		if tries >= 3 {
+			err = errors.Wrap(err, "giving up after 3 consecutive repeatable transaction failures")
+			return err
+		}
+		timepkg.Sleep(100 * timepkg.Millisecond)
+	}
+
+}
+
 func (s *RetryLayerSharedChannelStore) UpdateUserLastSyncAt(userID string, channelID string, remoteID string) error {
 
 	tries := 0

server/channels/store/sqlstore/channel_store.go

@@ -2070,22 +2070,34 @@ func (s SqlChannelStore) PatchMultipleMembersNotifyProps(members []*model.Channe
 	return updated, nil
 }
 
-func (s SqlChannelStore) GetMembers(channelID string, offset, limit int) (model.ChannelMembers, error) {
-	sql, args, err := s.channelMembersForTeamWithSchemeSelectQuery.
+func (s SqlChannelStore) GetMembers(opts model.ChannelMembersGetOptions) (model.ChannelMembers, error) {
+	query := s.channelMembersForTeamWithSchemeSelectQuery.
 		Where(sq.Eq{
-			"ChannelId": channelID,
-		}).
-		Limit(uint64(limit)).
-		Offset(uint64(offset)).
-		ToSql()
+			"ChannelId": opts.ChannelID,
+		})
+
+	if opts.UpdatedAfter > 0 {
+		query = query.Where(sq.Gt{"ChannelMembers.LastUpdateAt": opts.UpdatedAfter})
+		query = query.OrderBy("ChannelMembers.LastUpdateAt")
+	}
+
+	if opts.Limit > 0 {
+		query = query.Limit(uint64(opts.Limit))
+	}
+
+	if opts.Offset > 0 {
+		query = query.Offset(uint64(opts.Offset))
+	}
+
+	sql, args, err := query.ToSql()
 	if err != nil {
-		return nil, errors.Wrapf(err, "GetMember_ToSql ChannelID=%s", channelID)
+		return nil, errors.Wrapf(err, "GetMember_ToSql ChannelID=%s", opts.ChannelID)
 	}
 
 	dbMembers := channelMemberWithSchemeRolesList{}
 	err = s.GetReplica().Select(&dbMembers, sql, args...)
 	if err != nil {
-		return nil, errors.Wrapf(err, "failed to get ChannelMembers with channelId=%s", channelID)
+		return nil, errors.Wrapf(err, "failed to get ChannelMembers with channelId=%s", opts.ChannelID)
 	}
 
 	return dbMembers.ToModel(), nil

server/channels/store/sqlstore/shared_channel_store.go

@@ -417,6 +417,7 @@ func sharedChannelRemoteFields(prefix string) []string {
 		"COALESCE(" + prefix + "LastPostCreateID,'') AS LastPostCreateID",
 		prefix + "LastPostUpdateAt",
 		"COALESCE(" + prefix + "LastPostId,'') AS LastPostUpdateID",
+		prefix + "LastMembersSyncAt",
 	}
 }
 
@@ -708,6 +709,7 @@ func sharedChannelUserFields(prefix string) []string {
 		prefix + "RemoteId",
 		prefix + "CreateAt",
 		prefix + "LastSyncAt",
+		prefix + "LastMembershipSyncAt",
 	}
 }
 
@@ -720,7 +722,7 @@ func (s SqlSharedChannelStore) SaveUser(scUser *model.SharedChannelUser) (*model
 
 	query, args, err := s.getQueryBuilder().Insert("SharedChannelUsers").
 		Columns(sharedChannelUserFields("")...).
-		Values(scUser.Id, scUser.UserId, scUser.ChannelId, scUser.RemoteId, scUser.CreateAt, scUser.LastSyncAt).
+		Values(scUser.Id, scUser.UserId, scUser.ChannelId, scUser.RemoteId, scUser.CreateAt, scUser.LastSyncAt, scUser.LastMembershipSyncAt).
 		ToSql()
 	if err != nil {
 		return nil, errors.Wrapf(err, "savesharedchanneluser_tosql")
@@ -853,6 +855,25 @@ func (s SqlSharedChannelStore) UpdateUserLastSyncAt(userID string, channelID str
 	return nil
 }
 
+// UpdateUserLastMembershipSyncAt updates the LastMembershipSyncAt timestamp for the specified SharedChannelUser using the provided sync time.
+func (s SqlSharedChannelStore) UpdateUserLastMembershipSyncAt(userID string, channelID string, remoteID string, syncTime int64) error {
+	query := s.getQueryBuilder().
+		Update("SharedChannelUsers AS scu").
+		Set("LastMembershipSyncAt", sq.Expr("GREATEST(scu.LastMembershipSyncAt, ?)", syncTime)).
+		Where(sq.Eq{
+			"scu.UserId":    userID,
+			"scu.ChannelId": channelID,
+			"scu.RemoteId":  remoteID,
+		})
+
+	_, err := s.GetMaster().ExecBuilder(query)
+	if err != nil {
+		return fmt.Errorf("failed to update LastMembershipSyncAt for SharedChannelUser with userId=%s, channelId=%s, remoteId=%s: %w",
+			userID, channelID, remoteID, err)
+	}
+	return nil
+}
+
 func sharedChannelAttachementFields(prefix string) []string {
 	if prefix != "" && !strings.HasSuffix(prefix, ".") {
 		prefix = prefix + "."

server/channels/store/sqlstore/shared_channel_store_membership.go

@@ -0,0 +1,66 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package sqlstore
+
+import (
+	"database/sql"
+	"fmt"
+
+	"github.com/mattermost/mattermost/server/public/model"
+	sq "github.com/mattermost/squirrel"
+	"github.com/pkg/errors"
+)
+
+// UpdateRemoteMembershipCursor updates the LastMembersSyncAt timestamp for the specified SharedChannelRemote,
+// but only if the new timestamp is greater than the current value.
+func (s SqlSharedChannelStore) UpdateRemoteMembershipCursor(id string, syncTime int64) error {
+	query := s.getQueryBuilder().
+		Update("SharedChannelRemotes")
+
+	query = query.Set("LastMembersSyncAt", sq.Expr("GREATEST(LastMembersSyncAt, ?)", syncTime))
+
+	query = query.Where(sq.Eq{"Id": id})
+
+	result, err := s.GetMaster().ExecBuilder(query)
+	if err != nil {
+		return errors.Wrap(err, "failed to update membership cursor for SharedChannelRemote")
+	}
+
+	count, err := result.RowsAffected()
+	if err != nil {
+		return errors.Wrap(err, "failed to determine rows affected")
+	}
+
+	if count == 0 {
+		return fmt.Errorf("id not found: %s", id)
+	}
+
+	return nil
+}
+
+// GetUserChanges gets all SharedChannelUser changes for a given user, channel after a specific time.
+// This is used to detect if there are conflicting membership changes.
+func (s SqlSharedChannelStore) GetUserChanges(userID string, channelID string, afterTime int64) ([]*model.SharedChannelUser, error) {
+	squery, args, err := s.getQueryBuilder().
+		Select(sharedChannelUserFields("")...).
+		From("SharedChannelUsers").
+		Where(sq.Eq{"SharedChannelUsers.UserId": userID}).
+		Where(sq.Eq{"SharedChannelUsers.ChannelId": channelID}).
+		Where(sq.Gt{"SharedChannelUsers.LastSyncAt": afterTime}).
+		ToSql()
+
+	if err != nil {
+		return nil, errors.Wrapf(err, "getsharedchanneluserchanges_tosql")
+	}
+
+	users := []*model.SharedChannelUser{}
+	if err := s.GetReplica().Select(&users, squery, args...); err != nil {
+		if err == sql.ErrNoRows {
+			return make([]*model.SharedChannelUser, 0), nil
+		}
+		return nil, errors.Wrapf(err, "failed to find shared channel user changes with UserId=%s, ChannelId=%s, afterTime=%d",
+			userID, channelID, afterTime)
+	}
+	return users, nil
+}

server/channels/store/store.go

@@ -232,7 +232,7 @@ type ChannelStore interface {
 	// It replaces existing fields and creates new ones which don't exist.
 	UpdateMemberNotifyProps(channelID, userID string, props map[string]string) (*model.ChannelMember, error)
 	PatchMultipleMembersNotifyProps(members []*model.ChannelMemberIdentifier, notifyProps map[string]string) ([]*model.ChannelMember, error)
-	GetMembers(channelID string, offset, limit int) (model.ChannelMembers, error)
+	GetMembers(opts model.ChannelMembersGetOptions) (model.ChannelMembers, error)
 	GetMember(ctx context.Context, channelID string, userID string) (*model.ChannelMember, error)
 	GetMemberLastViewedAt(ctx context.Context, channelID string, userID string) (int64, error)
 	GetChannelMembersTimezones(channelID string) ([]model.StringMap, error)
@@ -1014,6 +1014,7 @@ type SharedChannelStore interface {
 	GetRemoteByIds(channelID string, remoteID string) (*model.SharedChannelRemote, error)
 	GetRemotes(offset, limit int, opts model.SharedChannelRemoteFilterOpts) ([]*model.SharedChannelRemote, error)
 	UpdateRemoteCursor(id string, cursor model.GetPostsSinceForSyncCursor) error
+	UpdateRemoteMembershipCursor(id string, syncTime int64) error
 	DeleteRemote(remoteID string) (bool, error)
 	GetRemotesStatus(channelID string) ([]*model.SharedChannelRemoteStatus, error)
 
@@ -1021,7 +1022,9 @@ type SharedChannelStore interface {
 	GetSingleUser(userID string, channelID string, remoteID string) (*model.SharedChannelUser, error)
 	GetUsersForUser(userID string) ([]*model.SharedChannelUser, error)
 	GetUsersForSync(filter model.GetUsersForSyncFilter) ([]*model.User, error)
+	GetUserChanges(userID string, channelID string, afterTime int64) ([]*model.SharedChannelUser, error)
 	UpdateUserLastSyncAt(userID string, channelID string, remoteID string) error
+	UpdateUserLastMembershipSyncAt(userID string, channelID string, remoteID string, syncTime int64) error
 
 	SaveAttachment(remote *model.SharedChannelAttachment) (*model.SharedChannelAttachment, error)
 	UpsertAttachment(remote *model.SharedChannelAttachment) (string, error)

server/channels/store/storetest/channel_store.go

@@ -73,6 +73,7 @@ func TestChannelStore(t *testing.T, rctx request.CTX, ss store.Store, s SqlStore
 	t.Run("Save", func(t *testing.T) { testChannelStoreSave(t, rctx, ss) })
 	t.Run("SaveDirectChannel", func(t *testing.T) { testChannelStoreSaveDirectChannel(t, rctx, ss, s) })
 	t.Run("CreateDirectChannel", func(t *testing.T) { testChannelStoreCreateDirectChannel(t, rctx, ss) })
+	t.Run("GetMembersWithCursorPagination", func(t *testing.T) { testChannelStoreGetMembersWithCursorPagination(t, rctx, ss) })
 	t.Run("Update", func(t *testing.T) { testChannelStoreUpdate(t, rctx, ss) })
 	t.Run("GetChannelUnread", func(t *testing.T) { testGetChannelUnread(t, rctx, ss) })
 	t.Run("Get", func(t *testing.T) { testChannelStoreGet(t, rctx, ss, s) })
@@ -265,7 +266,7 @@ func testChannelStoreSaveDirectChannel(t *testing.T, rctx request.CTX, ss store.
 	_, nErr = ss.Channel().SaveDirectChannel(rctx, &o1, &m1, &m2)
 	require.NoError(t, nErr, "couldn't save direct channel", nErr)
 
-	members, nErr := ss.Channel().GetMembers(o1.Id, 0, 100)
+	members, nErr := ss.Channel().GetMembers(model.ChannelMembersGetOptions{ChannelID: o1.Id, Offset: 0, Limit: 100})
 	require.NoError(t, nErr)
 	require.Len(t, members, 2, "should have saved 2 members")
 
@@ -305,7 +306,7 @@ func testChannelStoreSaveDirectChannel(t *testing.T, rctx request.CTX, ss store.
 	_, nErr = ss.Channel().SaveDirectChannel(rctx, &o1, &m1, &m1)
 	require.NoError(t, nErr, "couldn't save direct channel", nErr)
 
-	members, nErr = ss.Channel().GetMembers(o1.Id, 0, 100)
+	members, nErr = ss.Channel().GetMembers(model.ChannelMembersGetOptions{ChannelID: o1.Id, Offset: 0, Limit: 100})
 	require.NoError(t, nErr)
 	require.Len(t, members, 1, "should have saved just 1 member")
 
@@ -341,11 +342,72 @@ func testChannelStoreCreateDirectChannel(t *testing.T, rctx request.CTX, ss stor
 		ss.Channel().PermanentDelete(rctx, c1.Id)
 	}()
 
-	members, nErr := ss.Channel().GetMembers(c1.Id, 0, 100)
+	members, nErr := ss.Channel().GetMembers(model.ChannelMembersGetOptions{ChannelID: c1.Id, Offset: 0, Limit: 100})
 	require.NoError(t, nErr)
 	require.Len(t, members, 2, "should have saved 2 members")
 }
 
+// testChannelStoreGetMembersWithCursorPagination tests the cursor-based pagination functionality
+// of the GetMembers method, using the UpdatedAfter parameter to return only members that were
+// updated after a specific timestamp.
+func testChannelStoreGetMembersWithCursorPagination(t *testing.T, rctx request.CTX, ss store.Store) {
+	// Create two users
+	u1 := &model.User{}
+	u1.Email = MakeEmail()
+	u1.Nickname = model.NewId()
+	_, err := ss.User().Save(rctx, u1)
+	require.NoError(t, err)
+	_, nErr := ss.Team().SaveMember(rctx, &model.TeamMember{TeamId: model.NewId(), UserId: u1.Id}, -1)
+	require.NoError(t, nErr)
+
+	u2 := &model.User{}
+	u2.Email = MakeEmail()
+	u2.Nickname = model.NewId()
+	_, err = ss.User().Save(rctx, u2)
+	require.NoError(t, err)
+	_, nErr = ss.Team().SaveMember(rctx, &model.TeamMember{TeamId: model.NewId(), UserId: u2.Id}, -1)
+	require.NoError(t, nErr)
+
+	// Create direct channel between the users
+	c1, nErr := ss.Channel().CreateDirectChannel(rctx, u1, u2)
+	require.NoError(t, nErr, "couldn't create direct channel", nErr)
+	defer func() {
+		ss.Channel().PermanentDeleteMembersByChannel(rctx, c1.Id)
+		ss.Channel().PermanentDelete(rctx, c1.Id)
+	}()
+
+	// First get all members
+	members, nErr := ss.Channel().GetMembers(model.ChannelMembersGetOptions{ChannelID: c1.Id, Offset: 0, Limit: 100})
+	require.NoError(t, nErr)
+	require.Len(t, members, 2, "should have saved 2 members")
+
+	// Ensure members have different LastUpdateAt values by updating one of them after a short delay
+	time.Sleep(1 * time.Millisecond)
+	member := members[0]
+	_, err = ss.Channel().UpdateMember(rctx, &member)
+	require.NoError(t, err)
+
+	// Get members again after the update
+	members, nErr = ss.Channel().GetMembers(model.ChannelMembersGetOptions{ChannelID: c1.Id, Offset: 0, Limit: 100})
+	require.NoError(t, nErr)
+	require.Len(t, members, 2, "should have 2 members")
+
+	// Find member with smaller LastUpdateAt
+	sort.Slice(members, func(i, j int) bool {
+		return members[i].LastUpdateAt < members[j].LastUpdateAt
+	})
+	updateTime := members[0].LastUpdateAt
+
+	// Test cursor-based pagination by querying for members updated after that timestamp
+	membersAfter, nErr := ss.Channel().GetMembers(model.ChannelMembersGetOptions{
+		ChannelID:    c1.Id,
+		UpdatedAfter: updateTime,
+		Limit:        100,
+	})
+	require.NoError(t, nErr)
+	require.Len(t, membersAfter, 1, "should have found only 1 member created after the timestamp")
+}
+
 func testChannelStoreUpdate(t *testing.T, rctx request.CTX, ss store.Store) {
 	o1 := model.Channel{}
 	o1.TeamId = model.NewId()
@@ -7867,7 +7929,7 @@ func testChannelStoreRemoveAllDeactivatedMembers(t *testing.T, rctx request.CTX,
 	require.NoError(t, err)
 
 	// Get all the channel members. Check there are 3.
-	d1, err := ss.Channel().GetMembers(c1.Id, 0, 1000)
+	d1, err := ss.Channel().GetMembers(model.ChannelMembersGetOptions{ChannelID: c1.Id, Offset: 0, Limit: 1000})
 	assert.NoError(t, err)
 	assert.Len(t, d1, 3)
 
@@ -7887,7 +7949,7 @@ func testChannelStoreRemoveAllDeactivatedMembers(t *testing.T, rctx request.CTX,
 	assert.NoError(t, ss.Channel().RemoveAllDeactivatedMembers(rctx, c1.Id))
 
 	// Get all the channel members. Check there is now only 1: m3.
-	d2, err := ss.Channel().GetMembers(c1.Id, 0, 1000)
+	d2, err := ss.Channel().GetMembers(model.ChannelMembersGetOptions{ChannelID: c1.Id, Offset: 0, Limit: 1000})
 	assert.NoError(t, err)
 	assert.Len(t, d2, 1)
 	assert.Equal(t, u3.Id, d2[0].UserId)

server/channels/store/storetest/group_store.go

@@ -5340,7 +5340,7 @@ func groupTestpUpdateMembersRoleChannel(t *testing.T, rctx request.CTX, ss store
 			}
 			assert.ElementsMatch(t, tt.expectedUpdatedUsers, updatedUserIDs)
 
-			members, err := ss.Channel().GetMembers(channel.Id, 0, 100)
+			members, err := ss.Channel().GetMembers(model.ChannelMembersGetOptions{ChannelID: channel.Id, Offset: 0, Limit: 100})
 			require.NoError(t, err)
 			assert.GreaterOrEqual(t, len(members), 4) // sanity check for channel membership
 

server/channels/store/storetest/mocks/ChannelStore.go

@@ -1580,9 +1580,9 @@ func (_m *ChannelStore) GetMemberLastViewedAt(ctx context.Context, channelID str
 	return r0, r1
 }
 
-// GetMembers provides a mock function with given fields: channelID, offset, limit
-func (_m *ChannelStore) GetMembers(channelID string, offset int, limit int) (model.ChannelMembers, error) {
-	ret := _m.Called(channelID, offset, limit)
+// GetMembers provides a mock function with given fields: opts
+func (_m *ChannelStore) GetMembers(opts model.ChannelMembersGetOptions) (model.ChannelMembers, error) {
+	ret := _m.Called(opts)
 
 	if len(ret) == 0 {
 		panic("no return value specified for GetMembers")
@@ -1590,19 +1590,19 @@ func (_m *ChannelStore) GetMembers(channelID string, offset int, limit int) (mod
 
 	var r0 model.ChannelMembers
 	var r1 error
-	if rf, ok := ret.Get(0).(func(string, int, int) (model.ChannelMembers, error)); ok {
-		return rf(channelID, offset, limit)
+	if rf, ok := ret.Get(0).(func(model.ChannelMembersGetOptions) (model.ChannelMembers, error)); ok {
+		return rf(opts)
 	}
-	if rf, ok := ret.Get(0).(func(string, int, int) model.ChannelMembers); ok {
-		r0 = rf(channelID, offset, limit)
+	if rf, ok := ret.Get(0).(func(model.ChannelMembersGetOptions) model.ChannelMembers); ok {
+		r0 = rf(opts)
 	} else {
 		if ret.Get(0) != nil {
 			r0 = ret.Get(0).(model.ChannelMembers)
 		}
 	}
 
-	if rf, ok := ret.Get(1).(func(string, int, int) error); ok {
-		r1 = rf(channelID, offset, limit)
+	if rf, ok := ret.Get(1).(func(model.ChannelMembersGetOptions) error); ok {
+		r1 = rf(opts)
 	} else {
 		r1 = ret.Error(1)
 	}

server/channels/store/storetest/mocks/SharedChannelStore.go

@@ -368,6 +368,36 @@ func (_m *SharedChannelStore) GetSingleUser(userID string, channelID string, rem
 	return r0, r1
 }
 
+// GetUserChanges provides a mock function with given fields: userID, channelID, afterTime
+func (_m *SharedChannelStore) GetUserChanges(userID string, channelID string, afterTime int64) ([]*model.SharedChannelUser, error) {
+	ret := _m.Called(userID, channelID, afterTime)
+
+	if len(ret) == 0 {
+		panic("no return value specified for GetUserChanges")
+	}
+
+	var r0 []*model.SharedChannelUser
+	var r1 error
+	if rf, ok := ret.Get(0).(func(string, string, int64) ([]*model.SharedChannelUser, error)); ok {
+		return rf(userID, channelID, afterTime)
+	}
+	if rf, ok := ret.Get(0).(func(string, string, int64) []*model.SharedChannelUser); ok {
+		r0 = rf(userID, channelID, afterTime)
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).([]*model.SharedChannelUser)
+		}
+	}
+
+	if rf, ok := ret.Get(1).(func(string, string, int64) error); ok {
+		r1 = rf(userID, channelID, afterTime)
+	} else {
+		r1 = ret.Error(1)
+	}
+
+	return r0, r1
+}
+
 // GetUsersForSync provides a mock function with given fields: filter
 func (_m *SharedChannelStore) GetUsersForSync(filter model.GetUsersForSyncFilter) ([]*model.User, error) {
 	ret := _m.Called(filter)
@@ -700,6 +730,42 @@ func (_m *SharedChannelStore) UpdateRemoteCursor(id string, cursor model.GetPost
 	return r0
 }
 
+// UpdateRemoteMembershipCursor provides a mock function with given fields: id, syncTime
+func (_m *SharedChannelStore) UpdateRemoteMembershipCursor(id string, syncTime int64) error {
+	ret := _m.Called(id, syncTime)
+
+	if len(ret) == 0 {
+		panic("no return value specified for UpdateRemoteMembershipCursor")
+	}
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func(string, int64) error); ok {
+		r0 = rf(id, syncTime)
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}
+
+// UpdateUserLastMembershipSyncAt provides a mock function with given fields: userID, channelID, remoteID, syncTime
+func (_m *SharedChannelStore) UpdateUserLastMembershipSyncAt(userID string, channelID string, remoteID string, syncTime int64) error {
+	ret := _m.Called(userID, channelID, remoteID, syncTime)
+
+	if len(ret) == 0 {
+		panic("no return value specified for UpdateUserLastMembershipSyncAt")
+	}
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func(string, string, string, int64) error); ok {
+		r0 = rf(userID, channelID, remoteID, syncTime)
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}
+
 // UpdateUserLastSyncAt provides a mock function with given fields: userID, channelID, remoteID
 func (_m *SharedChannelStore) UpdateUserLastSyncAt(userID string, channelID string, remoteID string) error {
 	ret := _m.Called(userID, channelID, remoteID)

server/channels/store/timerlayer/timerlayer.go

@@ -1729,10 +1729,10 @@ func (s *TimerLayerChannelStore) GetMemberLastViewedAt(ctx context.Context, chan
 	return result, err
 }
 
-func (s *TimerLayerChannelStore) GetMembers(channelID string, offset int, limit int) (model.ChannelMembers, error) {
+func (s *TimerLayerChannelStore) GetMembers(opts model.ChannelMembersGetOptions) (model.ChannelMembers, error) {
 	start := time.Now()
 
-	result, err := s.ChannelStore.GetMembers(channelID, offset, limit)
+	result, err := s.ChannelStore.GetMembers(opts)
 
 	elapsed := float64(time.Since(start)) / float64(time.Second)
 	if s.Root.Metrics != nil {
@@ -9173,6 +9173,22 @@ func (s *TimerLayerSharedChannelStore) GetSingleUser(userID string, channelID st
 	return result, err
 }
 
+func (s *TimerLayerSharedChannelStore) GetUserChanges(userID string, channelID string, afterTime int64) ([]*model.SharedChannelUser, error) {
+	start := time.Now()
+
+	result, err := s.SharedChannelStore.GetUserChanges(userID, channelID, afterTime)
+
+	elapsed := float64(time.Since(start)) / float64(time.Second)
+	if s.Root.Metrics != nil {
+		success := "false"
+		if err == nil {
+			success = "true"
+		}
+		s.Root.Metrics.ObserveStoreMethodDuration("SharedChannelStore.GetUserChanges", success, elapsed)
+	}
+	return result, err
+}
+
 func (s *TimerLayerSharedChannelStore) GetUsersForSync(filter model.GetUsersForSyncFilter) ([]*model.User, error) {
 	start := time.Now()
 
@@ -9365,6 +9381,38 @@ func (s *TimerLayerSharedChannelStore) UpdateRemoteCursor(id string, cursor mode
 	return err
 }
 
+func (s *TimerLayerSharedChannelStore) UpdateRemoteMembershipCursor(id string, syncTime int64) error {
+	start := time.Now()
+
+	err := s.SharedChannelStore.UpdateRemoteMembershipCursor(id, syncTime)
+
+	elapsed := float64(time.Since(start)) / float64(time.Second)
+	if s.Root.Metrics != nil {
+		success := "false"
+		if err == nil {
+			success = "true"
+		}
+		s.Root.Metrics.ObserveStoreMethodDuration("SharedChannelStore.UpdateRemoteMembershipCursor", success, elapsed)
+	}
+	return err
+}
+
+func (s *TimerLayerSharedChannelStore) UpdateUserLastMembershipSyncAt(userID string, channelID string, remoteID string, syncTime int64) error {
+	start := time.Now()
+
+	err := s.SharedChannelStore.UpdateUserLastMembershipSyncAt(userID, channelID, remoteID, syncTime)
+
+	elapsed := float64(time.Since(start)) / float64(time.Second)
+	if s.Root.Metrics != nil {
+		success := "false"
+		if err == nil {
+			success = "true"
+		}
+		s.Root.Metrics.ObserveStoreMethodDuration("SharedChannelStore.UpdateUserLastMembershipSyncAt", success, elapsed)
+	}
+	return err
+}
+
 func (s *TimerLayerSharedChannelStore) UpdateUserLastSyncAt(userID string, channelID string, remoteID string) error {
 	start := time.Now()
 

server/platform/services/remotecluster/service.go

@@ -290,7 +290,7 @@ func (rcs *Service) pause() {
 	rcs.server.Log().Debug("Remote Cluster Service inactive")
 }
 
-// SetActive forces the service to be active or inactive
+// SetActive forces the service to be active or inactive for testing
 func (rcs *Service) SetActive(active bool) {
 	rcs.mux.Lock()
 	defer rcs.mux.Unlock()

server/platform/services/sharedchannel/channelinvite.go

@@ -89,6 +89,7 @@ func (scs *Service) SendChannelInvite(channel *model.Channel, userId string, rc
 			RemoteId:          rc.RemoteId,
 			IsInviteAccepted:  true,
 			IsInviteConfirmed: false,
+			LastMembersSyncAt: 0,
 		}
 		if _, err = scs.server.GetStore().SharedChannel().SaveRemote(scr); err != nil {
 			scs.sendEphemeralPost(channel.Id, userId, fmt.Sprintf("Error saving channel invite for %s: %v", rc.DisplayName, err))
@@ -134,6 +135,7 @@ func (scs *Service) SendChannelInvite(channel *model.Channel, userId string, rc
 		}
 
 		curTime := model.GetMillis()
+		var sharedChannelRemote *model.SharedChannelRemote
 		if existingScr != nil {
 			if existingScr.DeleteAt == 0 && existingScr.IsInviteConfirmed {
 				// the shared channel remote exists and is not
@@ -153,6 +155,7 @@ func (scs *Service) SendChannelInvite(channel *model.Channel, userId string, rc
 				scs.sendEphemeralPost(channel.Id, userId, fmt.Sprintf("Error confirming channel invite for %s: %v", rc.DisplayName, sErr))
 				return
 			}
+			sharedChannelRemote = existingScr
 		} else {
 			// the shared channel remote doesn't exists, so we create it
 			scr := &model.SharedChannelRemote{
@@ -163,15 +166,26 @@ func (scs *Service) SendChannelInvite(channel *model.Channel, userId string, rc
 				IsInviteConfirmed: true,
 				LastPostCreateAt:  curTime,
 				LastPostUpdateAt:  curTime,
+				LastMembersSyncAt: 0,
 			}
 			if _, err = scs.server.GetStore().SharedChannel().SaveRemote(scr); err != nil {
 				scs.sendEphemeralPost(channel.Id, userId, fmt.Sprintf("Error confirming channel invite for %s: %v", rc.DisplayName, err))
 				return
 			}
+			sharedChannelRemote = scr
 		}
 
 		scs.NotifyChannelChanged(sc.ChannelId)
 		scs.sendEphemeralPost(channel.Id, userId, fmt.Sprintf("`%s` has been added to channel.", rc.DisplayName))
+
+		// Sync all channel members to the remote now that the remote entry exists
+		if syncErr := scs.SyncAllChannelMembers(sc.ChannelId, rc.RemoteId, sharedChannelRemote); syncErr != nil {
+			scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to sync channel members after invite confirmation",
+				mlog.String("channel_id", sc.ChannelId),
+				mlog.String("remote_id", rc.RemoteId),
+				mlog.Err(syncErr),
+			)
+		}
 	}
 
 	if rc.IsPlugin() {
@@ -311,6 +325,15 @@ func (scs *Service) onReceiveChannelInvite(msg model.RemoteClusterMsg, rc *model
 		if _, err := scs.server.GetStore().SharedChannel().UpdateRemote(existingScr); err != nil {
 			return fmt.Errorf("cannot restore deleted shared channel remote (channel_id=%s): %w", invite.ChannelId, err)
 		}
+
+		// Sync local channel members to the remote after restoring the shared channel
+		if syncErr := scs.SyncAllChannelMembers(channel.Id, rc.RemoteId, existingScr); syncErr != nil {
+			scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to sync local channel members after restoring shared channel",
+				mlog.String("channel_id", channel.Id),
+				mlog.String("remote_id", rc.RemoteId),
+				mlog.Err(syncErr),
+			)
+		}
 	} else {
 		creatorID := channel.CreatorId
 		if creatorID == "" {
@@ -325,6 +348,7 @@ func (scs *Service) onReceiveChannelInvite(msg model.RemoteClusterMsg, rc *model
 			RemoteId:          rc.RemoteId,
 			LastPostCreateAt:  model.GetMillis(),
 			LastPostUpdateAt:  model.GetMillis(),
+			LastMembersSyncAt: 0,
 		}
 
 		if _, err := scs.server.GetStore().SharedChannel().SaveRemote(scr); err != nil {
@@ -336,6 +360,15 @@ func (scs *Service) onReceiveChannelInvite(msg model.RemoteClusterMsg, rc *model
 			scs.server.GetStore().SharedChannel().Delete(sharedChannel.ChannelId)
 			return fmt.Errorf("cannot create shared channel remote (channel_id=%s): %w", invite.ChannelId, err)
 		}
+
+		// Sync local channel members to the remote after accepting the invitation
+		if syncErr := scs.SyncAllChannelMembers(channel.Id, rc.RemoteId, scr); syncErr != nil {
+			scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to sync local channel members after accepting invitation",
+				mlog.String("channel_id", channel.Id),
+				mlog.String("remote_id", rc.RemoteId),
+				mlog.Err(syncErr),
+			)
+		}
 	}
 	return nil
 }

server/platform/services/sharedchannel/channelinvite_test.go

@@ -29,6 +29,18 @@ var (
 	mockTypeContext    = mock.MatchedBy(func(ctx context.Context) bool { return true })
 )
 
+// setupMockServerWithConfig sets up the standard mocks that all tests need
+func setupMockServerWithConfig(mockServer *MockServerIface) {
+	// Mock Config for feature flag check - disable membership sync to avoid complex mocking
+	mockConfig := model.Config{}
+	mockConfig.SetDefaults()
+	mockConfig.FeatureFlags.EnableSharedChannelsMemberSync = false
+	mockServer.On("Config").Return(&mockConfig)
+
+	// Mock GetRemoteClusterService for feature flag check
+	mockServer.On("GetRemoteClusterService").Return(nil)
+}
+
 func TestOnReceiveChannelInvite(t *testing.T) {
 	t.Run("when msg payload is empty, it does nothing", func(t *testing.T) {
 		mockServer := &MockServerIface{}
@@ -92,6 +104,8 @@ func TestOnReceiveChannelInvite(t *testing.T) {
 		mockStore.On("SharedChannel").Return(&mockSharedChannelStore)
 
 		mockServer.On("GetStore").Return(mockStore)
+		setupMockServerWithConfig(mockServer)
+
 		createPostPermission := model.ChannelModeratedPermissionsMap[model.PermissionCreatePost.Id]
 		createReactionPermission := model.ChannelModeratedPermissionsMap[model.PermissionAddReaction.Id]
 		updateMap := model.ChannelModeratedRolesPatch{
@@ -216,6 +230,8 @@ func TestOnReceiveChannelInvite(t *testing.T) {
 		mockStore.On("SharedChannel").Return(&mockSharedChannelStore)
 
 		mockServer.On("GetStore").Return(mockStore)
+		setupMockServerWithConfig(mockServer)
+
 		defer mockApp.AssertExpectations(t)
 
 		err = scs.onReceiveChannelInvite(msg, remoteCluster, nil)
@@ -351,6 +367,7 @@ func TestOnReceiveChannelInvite(t *testing.T) {
 
 				mockServer = scs.server.(*MockServerIface)
 				mockServer.On("GetStore").Return(mockStore)
+				setupMockServerWithConfig(mockServer)
 
 				mockApp.On("GetOrCreateDirectChannel", mockTypeReqContext, mockTypeString, mockTypeString, mock.AnythingOfType("model.ChannelOption")).
 					Return(channel, nil).Maybe()

server/platform/services/sharedchannel/membership.go

@@ -0,0 +1,409 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package sharedchannel
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"time"
+
+	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/public/shared/mlog"
+	"github.com/mattermost/mattermost/server/v8/platform/services/remotecluster"
+)
+
+// isChannelMemberSyncEnabled checks if the feature flag is enabled and remote cluster service is available
+func (scs *Service) isChannelMemberSyncEnabled() bool {
+	featureFlagEnabled := scs.server.Config().FeatureFlags.EnableSharedChannelsMemberSync
+	remoteClusterService := scs.server.GetRemoteClusterService()
+	return featureFlagEnabled && remoteClusterService != nil
+}
+
+// queueMembershipSyncTask creates and queues a task to synchronize channel membership changes
+func (scs *Service) queueMembershipSyncTask(channelID, userID, remoteID string, syncMsg *model.SyncMsg, retryMsg *model.SyncMsg) {
+	task := newSyncTask(channelID, userID, remoteID, syncMsg, retryMsg)
+	task.schedule = time.Now().Add(NotifyMinimumDelay)
+
+	scs.addTask(task)
+}
+
+// HandleMembershipChange is called when users are added or removed from a shared channel.
+// It creates a task to notify all remote clusters about the membership change.
+func (scs *Service) HandleMembershipChange(channelID, userID string, isAdd bool, remoteID string) {
+	if !scs.isChannelMemberSyncEnabled() {
+		return
+	}
+
+	// Create timestamp for consistent usage
+	changeTime := model.GetMillis()
+
+	// Create membership change info
+	syncMsg := model.NewSyncMsg(channelID)
+	syncMsg.MembershipChanges = []*model.MembershipChangeMsg{
+		{
+			ChannelId:  channelID,
+			UserId:     userID,
+			IsAdd:      isAdd,
+			RemoteId:   remoteID, // which remote initiated this change
+			ChangeTime: changeTime,
+		},
+	}
+
+	// Queue the membership change task
+	scs.queueMembershipSyncTask(channelID, userID, "", syncMsg, nil)
+}
+
+// HandleMembershipBatchChange is called to process a batch of membership changes for a shared channel.
+// It creates a task to notify all remote clusters about the batch membership changes.
+func (scs *Service) HandleMembershipBatchChange(channelID string, userIDs []string, isAdd bool, remoteID string) {
+	if !scs.isChannelMemberSyncEnabled() {
+		return
+	}
+
+	if len(userIDs) == 0 {
+		return
+	}
+
+	// Create timestamp for consistent usage
+	changeTime := model.GetMillis()
+
+	// Create sync message with membership changes
+	syncMsg := model.NewSyncMsg(channelID)
+	syncMsg.MembershipChanges = make([]*model.MembershipChangeMsg, 0, len(userIDs))
+
+	// Add each user to the batch
+	for _, userID := range userIDs {
+		syncMsg.MembershipChanges = append(syncMsg.MembershipChanges, &model.MembershipChangeMsg{
+			ChannelId:  channelID,
+			UserId:     userID,
+			IsAdd:      isAdd,
+			RemoteId:   remoteID,
+			ChangeTime: changeTime,
+		})
+	}
+
+	// Queue the batch membership sync task
+	scs.queueMembershipSyncTask(channelID, "", "", syncMsg, nil)
+}
+
+// SyncAllChannelMembers synchronizes all channel members to a specific remote.
+// This is typically called when a channel is first shared with a remote cluster.
+// If remote is provided, it will be used instead of fetching from the database.
+func (scs *Service) SyncAllChannelMembers(channelID string, remoteID string, remote *model.SharedChannelRemote) error {
+	if !scs.isChannelMemberSyncEnabled() {
+		return nil
+	}
+
+	// Verify the channel exists and is shared
+	if _, err := scs.server.GetStore().SharedChannel().Get(channelID); err != nil {
+		scs.server.Log().Log(mlog.LvlSharedChannelServiceDebug, "Failed to get shared channel",
+			mlog.String("channel_id", channelID),
+			mlog.Err(err),
+		)
+		return fmt.Errorf("failed to get shared channel %s: %w", channelID, err)
+	}
+
+	// Get the remote to ensure it exists (if not provided)
+	if remote == nil {
+		var err error
+		remote, err = scs.server.GetStore().SharedChannel().GetRemoteByIds(channelID, remoteID)
+		if err != nil {
+			scs.server.Log().Log(mlog.LvlSharedChannelServiceDebug, "Failed to get remote",
+				mlog.String("channel_id", channelID),
+				mlog.String("remote_id", remoteID),
+				mlog.Err(err),
+			)
+			return fmt.Errorf("failed to get remote for channel %s: %w", channelID, err)
+		}
+	}
+
+	// Use offset-based pagination to handle channels with many members
+	// This ensures we don't skip members when multiple members have the same LastUpdateAt timestamp
+	maxPerPage := scs.GetMemberSyncBatchSize()
+	var allMembers model.ChannelMembers
+	lastSyncAt := remote.LastMembersSyncAt
+	offset := 0
+
+	// Process members incrementally with offset-based pagination
+	for {
+		opts := model.ChannelMembersGetOptions{
+			ChannelID:    channelID,
+			UpdatedAfter: lastSyncAt,
+			Limit:        maxPerPage,
+			Offset:       offset,
+		}
+
+		members, err1 := scs.server.GetStore().Channel().GetMembers(opts)
+		if err1 != nil {
+			return fmt.Errorf("failed to get members for channel %s: %w", channelID, err1)
+		}
+
+		if len(members) == 0 {
+			break // No more members to process
+		}
+
+		// Add to our collection
+		allMembers = append(allMembers, members...)
+
+		// Log progress when processing large channels
+		if len(allMembers)%1000 == 0 {
+			scs.server.Log().Log(mlog.LvlSharedChannelServiceDebug, "Processing channel members in batches",
+				mlog.String("channel_id", channelID),
+				mlog.String("remote_id", remoteID),
+				mlog.Int("processed_so_far", len(allMembers)),
+			)
+		}
+
+		if len(members) < maxPerPage {
+			break // Last page
+		}
+
+		// Move to next page
+		offset += maxPerPage
+	}
+
+	if len(allMembers) == 0 {
+		scs.server.Log().Log(mlog.LvlSharedChannelServiceDebug, "No members to sync for channel",
+			mlog.String("channel_id", channelID),
+			mlog.String("remote_id", remoteID),
+		)
+		return nil
+	}
+
+	scs.server.Log().Log(mlog.LvlSharedChannelServiceDebug, "Syncing all channel members",
+		mlog.String("channel_id", channelID),
+		mlog.String("remote_id", remoteID),
+		mlog.Int("member_count", len(allMembers)),
+	)
+
+	// Get batch size from config
+	batchSize := scs.GetMemberSyncBatchSize()
+
+	// For small channels, queue individual membership changes
+	if len(allMembers) <= batchSize {
+		return scs.syncMembersIndividually(channelID, remoteID, allMembers, remote)
+	}
+
+	// For larger channels, use batch processing
+	return scs.syncMembersInBatches(channelID, remoteID, allMembers, remote)
+}
+
+// syncMembersIndividually processes each member individually
+// This is more efficient for small channels
+func (scs *Service) syncMembersIndividually(channelID, remoteID string, members model.ChannelMembers, remote *model.SharedChannelRemote) error {
+	// Queue individual membership changes for each member
+	for _, member := range members {
+		// Queue membership change for this user (isAdd=true)
+		scs.HandleMembershipChange(channelID, member.UserId, true, "")
+	}
+
+	return nil
+}
+
+// syncMembersInBatches processes members in batches for greater efficiency
+// This is better for channels with many members
+func (scs *Service) syncMembersInBatches(channelID, remoteID string, members model.ChannelMembers, remote *model.SharedChannelRemote) error {
+	// Get batch size from config
+	batchSize := scs.GetMemberSyncBatchSize()
+
+	for i := 0; i < len(members); i += batchSize {
+		end := i + batchSize
+		if end > len(members) {
+			end = len(members)
+		}
+
+		// Create a batch of members
+		batchMembers := members[i:end]
+
+		// Extract user IDs from the batch
+		userIDs := make([]string, len(batchMembers))
+		for j, member := range batchMembers {
+			userIDs[j] = member.UserId
+		}
+
+		// Use the batch handling function to queue the changes
+		scs.HandleMembershipBatchChange(channelID, userIDs, true, "")
+	}
+
+	return nil
+}
+
+// processMembershipChange processes a channel membership change task.
+// It determines which remotes should receive the update and creates tasks for each.
+func (scs *Service) processMembershipChange(syncMsg *model.SyncMsg) {
+	if len(syncMsg.MembershipChanges) == 0 {
+		scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Invalid membership change task - no membership changes",
+			mlog.String("channel_id", syncMsg.ChannelId),
+		)
+		return
+	}
+
+	// Get the shared channel (to verify it exists)
+	_, err := scs.server.GetStore().SharedChannel().Get(syncMsg.ChannelId)
+	if err != nil {
+		scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to get shared channel for membership change",
+			mlog.String("channel_id", syncMsg.ChannelId),
+			mlog.Int("change_count", len(syncMsg.MembershipChanges)),
+			mlog.Err(err),
+		)
+		return
+	}
+
+	// Get all remotes for this channel
+	remotes, err := scs.server.GetStore().SharedChannel().GetRemotes(0, 999999, model.SharedChannelRemoteFilterOpts{
+		ChannelId: syncMsg.ChannelId,
+	})
+	if err != nil {
+		scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to get shared channel remotes for membership change",
+			mlog.String("channel_id", syncMsg.ChannelId),
+			mlog.Err(err),
+		)
+		return
+	}
+
+	// Always use batch processing for consistency (works for single or multiple changes)
+	scs.syncMembershipBatchToRemotes(syncMsg, remotes)
+}
+
+// syncMembershipBatchToRemotes synchronizes membership changes (single or batch) with remote clusters.
+func (scs *Service) syncMembershipBatchToRemotes(syncMsg *model.SyncMsg, remotes []*model.SharedChannelRemote) {
+	if len(syncMsg.MembershipChanges) == 0 {
+		return
+	}
+
+	// Get the initiating remote ID from the first change (all should be the same)
+	initiatingRemoteId := ""
+	if len(syncMsg.MembershipChanges) > 0 {
+		initiatingRemoteId = syncMsg.MembershipChanges[0].RemoteId
+	}
+
+	// Send to all remotes except the one that initiated this change
+	for _, remote := range remotes {
+		// Skip the remote that initiated this change to prevent loops
+		if remote.RemoteId == initiatingRemoteId {
+			continue
+		}
+
+		// Get the remote cluster
+		rc, err := scs.server.GetStore().RemoteCluster().Get(remote.RemoteId, false)
+		if err != nil {
+			scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to get remote cluster for batch membership sync",
+				mlog.String("remote_id", remote.RemoteId),
+				mlog.String("channel_id", syncMsg.ChannelId),
+				mlog.Err(err),
+			)
+			continue
+		}
+
+		// Create a copy of the sync message to potentially add user profiles
+		enrichedSyncMsg := &model.SyncMsg{
+			Id:                syncMsg.Id,
+			ChannelId:         syncMsg.ChannelId,
+			MembershipChanges: syncMsg.MembershipChanges,
+			Users:             make(map[string]*model.User),
+		}
+
+		// Add user profiles for all users being added
+		for _, change := range syncMsg.MembershipChanges {
+			if change.IsAdd {
+				user, pErr := scs.server.GetStore().User().Get(context.Background(), change.UserId)
+				if pErr != nil {
+					scs.server.Log().Log(mlog.LvlSharedChannelServiceWarn, "Failed to get user for batch membership sync",
+						mlog.String("user_id", change.UserId),
+						mlog.String("channel_id", syncMsg.ChannelId),
+						mlog.String("remote_id", remote.RemoteId),
+						mlog.Err(pErr),
+					)
+					continue
+				}
+
+				// Check if user profile needs to be synced
+				doSync, _, sErr := scs.shouldUserSync(user, syncMsg.ChannelId, rc)
+				if sErr == nil && doSync {
+					enrichedSyncMsg.Users[user.Id] = user
+				}
+			}
+		}
+
+		// Send message using the existing remote cluster framework
+		payload, err := json.Marshal(enrichedSyncMsg)
+		if err != nil {
+			scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to marshal batch membership message",
+				mlog.String("remote_id", remote.RemoteId),
+				mlog.String("channel_id", syncMsg.ChannelId),
+				mlog.Err(err),
+			)
+			continue
+		}
+
+		msg := model.RemoteClusterMsg{
+			Id:       model.NewId(),
+			Topic:    TopicChannelMembership,
+			CreateAt: model.GetMillis(),
+			Payload:  payload,
+		}
+
+		ctx, cancel := context.WithTimeout(context.Background(), remotecluster.SendTimeout)
+		defer cancel()
+
+		// Define a callback function
+		callback := func(msg model.RemoteClusterMsg, rc *model.RemoteCluster, resp *remotecluster.Response, err error) {
+			if err != nil {
+				scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Error sending batch membership changes to remote",
+					mlog.String("remote", remote.RemoteId),
+					mlog.String("channel_id", syncMsg.ChannelId),
+					mlog.Int("change_count", len(syncMsg.MembershipChanges)),
+					mlog.Err(err),
+				)
+				return
+			}
+
+			if resp != nil && resp.Err != "" {
+				scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Remote error when processing batch membership changes",
+					mlog.String("remote", remote.RemoteId),
+					mlog.String("channel_id", syncMsg.ChannelId),
+					mlog.String("remote_error", resp.Err),
+				)
+				return
+			}
+
+			// Update sync timestamps
+			for _, change := range syncMsg.MembershipChanges {
+				if err := scs.server.GetStore().SharedChannel().UpdateUserLastMembershipSyncAt(change.UserId, change.ChannelId, remote.RemoteId, change.ChangeTime); err != nil {
+					scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to update user membership sync timestamp in batch",
+						mlog.String("user_id", change.UserId),
+						mlog.Err(err),
+					)
+				}
+			}
+
+			// Update the cursor with the latest change time
+			var maxChangeTime int64
+			for _, change := range syncMsg.MembershipChanges {
+				if change.ChangeTime > maxChangeTime {
+					maxChangeTime = change.ChangeTime
+				}
+			}
+
+			if err := scs.updateMembershipSyncCursor(syncMsg.ChannelId, remote.RemoteId, maxChangeTime); err != nil {
+				scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to update membership sync cursor for batch",
+					mlog.String("remote_id", remote.RemoteId),
+					mlog.String("channel_id", syncMsg.ChannelId),
+					mlog.Err(err),
+				)
+			}
+		}
+
+		err = scs.server.GetRemoteClusterService().SendMsg(ctx, msg, rc, callback)
+
+		if err != nil {
+			scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to send batch membership changes to remote",
+				mlog.String("remote_id", remote.RemoteId),
+				mlog.String("channel_id", syncMsg.ChannelId),
+				mlog.Err(err),
+			)
+		}
+	}
+}

server/platform/services/sharedchannel/membership_recv.go

@@ -0,0 +1,213 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package sharedchannel
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/public/shared/mlog"
+	"github.com/mattermost/mattermost/server/public/shared/request"
+	"github.com/mattermost/mattermost/server/v8/platform/services/remotecluster"
+)
+
+// checkMembershipConflict checks if there are newer changes that would conflict with this one
+// Returns true if this change should be skipped due to a conflict
+func (scs *Service) checkMembershipConflict(userID, channelID string, changeTime int64) (bool, error) {
+	conflicts, err := scs.server.GetStore().SharedChannel().GetUserChanges(userID, channelID, changeTime)
+	if err != nil {
+		scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to check for membership change conflicts",
+			mlog.String("user_id", userID),
+			mlog.String("channel_id", channelID),
+			mlog.Err(err),
+		)
+		return false, err
+	}
+
+	// If there are conflicting operations, the latest one wins
+	for _, conflict := range conflicts {
+		if conflict.LastMembershipSyncAt > changeTime {
+			scs.server.Log().Log(mlog.LvlSharedChannelServiceDebug, "Ignoring older membership change due to conflict",
+				mlog.String("user_id", userID),
+				mlog.String("channel_id", channelID),
+				mlog.Int("change_time", int(changeTime)),
+				mlog.Int("conflicting_time", int(conflict.LastMembershipSyncAt)),
+			)
+			return true, nil
+		}
+	}
+
+	return false, nil
+}
+
+// onReceiveMembershipChanges processes channel membership changes from a remote cluster
+func (scs *Service) onReceiveMembershipChanges(syncMsg *model.SyncMsg, rc *model.RemoteCluster, response *remotecluster.Response) error {
+	// Check if feature flag is enabled
+	if !scs.server.Config().FeatureFlags.EnableSharedChannelsMemberSync {
+		return nil
+	}
+
+	if len(syncMsg.MembershipChanges) == 0 {
+		return fmt.Errorf("onReceiveMembershipChanges: no membership changes")
+	}
+
+	// Get the channel to make sure it exists and is shared
+	channel, err := scs.server.GetStore().Channel().Get(syncMsg.ChannelId, true)
+	if err != nil {
+		return fmt.Errorf("cannot get channel for membership changes: %w", err)
+	}
+
+	// Verify this is a valid shared channel
+	_, err = scs.server.GetStore().SharedChannel().Get(syncMsg.ChannelId)
+	if err != nil {
+		return fmt.Errorf("cannot get shared channel for membership changes: %w", err)
+	}
+
+	// Calculate the maximum ChangeTime from all changes in the batch
+	var maxChangeTime int64
+	for _, change := range syncMsg.MembershipChanges {
+		if change.ChangeTime > maxChangeTime {
+			maxChangeTime = change.ChangeTime
+		}
+	}
+
+	// Process each change
+	var successCount, skipCount, failCount int
+
+	for _, change := range syncMsg.MembershipChanges {
+		// Check for conflicts
+		shouldSkip, _ := scs.checkMembershipConflict(change.UserId, change.ChannelId, change.ChangeTime)
+		if shouldSkip {
+			skipCount++
+			continue
+		}
+
+		// Process the membership change based on whether it's an add or remove
+		var processErr error
+		if change.IsAdd {
+			scs.server.Log().Log(mlog.LvlSharedChannelServiceDebug, "Adding user to channel from remote cluster",
+				mlog.String("user_id", change.UserId),
+				mlog.String("channel_id", change.ChannelId),
+				mlog.String("remote_id", rc.RemoteId),
+			)
+			processErr = scs.processMemberAdd(change, channel, rc, maxChangeTime)
+		} else {
+			scs.server.Log().Log(mlog.LvlSharedChannelServiceDebug, "Removing user from channel from remote cluster",
+				mlog.String("user_id", change.UserId),
+				mlog.String("channel_id", change.ChannelId),
+				mlog.String("remote_id", rc.RemoteId),
+			)
+			processErr = scs.processMemberRemove(change, rc, maxChangeTime)
+		}
+
+		if processErr != nil {
+			scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to process membership change",
+				mlog.String("user_id", change.UserId),
+				mlog.String("channel_id", change.ChannelId),
+				mlog.String("remote_id", rc.RemoteId),
+				mlog.Bool("is_add", change.IsAdd),
+				mlog.Err(processErr),
+			)
+			failCount++
+			continue
+		}
+
+		successCount++
+	}
+
+	return nil
+}
+
+// processMemberAdd handles adding a user to a channel as part of batch processing
+func (scs *Service) processMemberAdd(change *model.MembershipChangeMsg, channel *model.Channel, rc *model.RemoteCluster, maxChangeTime int64) error {
+	// Get the user if they exist
+	user, err := scs.server.GetStore().User().Get(request.EmptyContext(scs.server.Log()).Context(), change.UserId)
+	if err != nil {
+		return fmt.Errorf("cannot get user for channel add: %w", err)
+	}
+
+	// Check user permissions for private channels
+	if channel.Type == model.ChannelTypePrivate {
+		// Add user to team if needed for private channel
+		rctx := request.EmptyContext(scs.server.Log())
+		appErr := scs.app.AddUserToTeamByTeamId(rctx, channel.TeamId, user)
+		if appErr != nil {
+			return fmt.Errorf("cannot add user to team for private channel: %w", appErr)
+		}
+	}
+
+	// Use the app layer to add the user to the channel
+	// This ensures proper processing of all side effects
+	rctx := request.EmptyContext(scs.server.Log())
+	_, appErr := scs.app.AddUserToChannel(rctx, user, channel, false)
+	if appErr != nil {
+		// Skip "already added" errors
+		if appErr.Error() != "api.channel.add_user.to_channel.failed.app_error" &&
+			!strings.Contains(appErr.Error(), "channel_member_exists") {
+			return fmt.Errorf("cannot add user to channel: %w", appErr)
+		}
+		// User is already in the channel, which is fine
+	}
+
+	// Update the sync status
+	if syncErr := scs.server.GetStore().SharedChannel().UpdateUserLastMembershipSyncAt(change.UserId, change.ChannelId, rc.RemoteId, maxChangeTime); syncErr != nil {
+		scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to update user LastMembershipSyncAt after batch member add",
+			mlog.String("user_id", change.UserId),
+			mlog.String("channel_id", change.ChannelId),
+			mlog.String("remote_id", rc.RemoteId),
+			mlog.Err(syncErr),
+		)
+		// Continue despite the error - this is not critical
+	}
+
+	return nil
+}
+
+// processMemberRemove handles removing a user from a channel as part of batch processing
+func (scs *Service) processMemberRemove(change *model.MembershipChangeMsg, rc *model.RemoteCluster, maxChangeTime int64) error {
+	// Get channel so we can use app layer methods properly
+	channel, err := scs.server.GetStore().Channel().Get(change.ChannelId, true)
+	if err != nil {
+		scs.server.Log().Log(mlog.LvlSharedChannelServiceWarn, "Cannot find channel for member removal",
+			mlog.String("channel_id", change.ChannelId),
+			mlog.String("user_id", change.UserId),
+			mlog.Err(err),
+		)
+		// Continue anyway to update sync status - the channel might be deleted
+	}
+
+	// Use the app layer's remove user method if channel still exists
+	if channel != nil {
+		rctx := request.EmptyContext(scs.server.Log())
+		// We use empty string for removerUserId to indicate system-initiated removal
+		// This also ensures we bypass permission checks intended for user-initiated removals
+		appErr := scs.app.RemoveUserFromChannel(rctx, change.UserId, "", channel)
+		if appErr != nil {
+			// Ignore "not found" errors - the user might already be removed
+			if !strings.Contains(appErr.Error(), "store.sql_channel.remove_member.missing.app_error") {
+				scs.server.Log().Log(mlog.LvlSharedChannelServiceWarn, "Error removing user from channel",
+					mlog.String("channel_id", change.ChannelId),
+					mlog.String("user_id", change.UserId),
+					mlog.Err(appErr),
+				)
+				// Continue anyway to update sync status - don't return error here
+				// to ensure sync status still gets updated
+			}
+		}
+	}
+
+	// Update the sync status
+	if syncErr := scs.server.GetStore().SharedChannel().UpdateUserLastMembershipSyncAt(change.UserId, change.ChannelId, rc.RemoteId, maxChangeTime); syncErr != nil {
+		scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to update user LastMembershipSyncAt after batch member remove",
+			mlog.String("user_id", change.UserId),
+			mlog.String("channel_id", change.ChannelId),
+			mlog.String("remote_id", rc.RemoteId),
+			mlog.Err(syncErr),
+		)
+		// Continue despite the error - this is not critical
+	}
+
+	return nil
+}

server/platform/services/sharedchannel/mock_AppIface_test.go

@@ -513,6 +513,26 @@ func (_m *MockAppIface) Publish(message *model.WebSocketEvent) {
 	_m.Called(message)
 }
 
+// RemoveUserFromChannel provides a mock function with given fields: c, userID, removerUserId, channel
+func (_m *MockAppIface) RemoveUserFromChannel(c request.CTX, userID string, removerUserId string, channel *model.Channel) *model.AppError {
+	ret := _m.Called(c, userID, removerUserId, channel)
+
+	if len(ret) == 0 {
+		panic("no return value specified for RemoveUserFromChannel")
+	}
+
+	var r0 *model.AppError
+	if rf, ok := ret.Get(0).(func(request.CTX, string, string, *model.Channel) *model.AppError); ok {
+		r0 = rf(c, userID, removerUserId, channel)
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).(*model.AppError)
+		}
+	}
+
+	return r0
+}
+
 // SaveAndBroadcastStatus provides a mock function with given fields: status
 func (_m *MockAppIface) SaveAndBroadcastStatus(status *model.Status) {
 	_m.Called(status)

server/platform/services/sharedchannel/service.go

@@ -24,6 +24,7 @@ const (
 	TopicSync                    = "sharedchannel_sync"
 	TopicChannelInvite           = "sharedchannel_invite"
 	TopicUploadCreate            = "sharedchannel_upload"
+	TopicChannelMembership       = "sharedchannel_membership"
 	TopicGlobalUserSync          = "sharedchannel_global_user_sync"
 	MaxRetries                   = 3
 	MaxUsersPerSync              = 25
@@ -31,6 +32,7 @@ const (
 	NotifyMinimumDelay           = time.Second * 2
 	MaxUpsertRetries             = 25
 	ProfileImageSyncTimeout      = time.Second * 5
+	// Default value for MaxMembersPerBatch is defined in config.go as ConnectedWorkspacesSettingsDefaultMemberSyncBatchSize
 )
 
 // Mocks can be re-generated with `make sharedchannel-mocks`.
@@ -58,6 +60,7 @@ type AppIface interface {
 	UserCanSeeOtherUser(c request.CTX, userID string, otherUserId string) (bool, *model.AppError)
 	AddUserToChannel(c request.CTX, user *model.User, channel *model.Channel, skipTeamMemberIntegrityCheck bool) (*model.ChannelMember, *model.AppError)
 	AddUserToTeamByTeamId(c request.CTX, teamId string, user *model.User) *model.AppError
+	RemoveUserFromChannel(c request.CTX, userID string, removerUserId string, channel *model.Channel) *model.AppError
 	PermanentDeleteChannel(c request.CTX, channel *model.Channel) *model.AppError
 	CreatePost(c request.CTX, post *model.Post, channel *model.Channel, flags model.CreatePostFlags) (savedPost *model.Post, err *model.AppError)
 	UpdatePost(c request.CTX, post *model.Post, updatePostOptions *model.UpdatePostOptions) (*model.Post, *model.AppError)
@@ -90,9 +93,10 @@ type Service struct {
 	changeSignal chan struct{}
 
 	// everything below guarded by `mux`
-	mux                       sync.RWMutex
-	active                    bool
-	leaderListenerId          string
+	mux              sync.RWMutex
+	active           bool
+	leaderListenerId string
+
 	connectionStateListenerId string
 	done                      chan struct{}
 	tasks                     map[string]syncTask
@@ -136,6 +140,8 @@ func (scs *Service) Start() error {
 	scs.connectionStateListenerId = rcs.AddConnectionStateListener(scs.onConnectionStateChange)
 	scs.mux.Unlock()
 
+	rcs.AddTopicListener(TopicChannelMembership, scs.onReceiveSyncMessage)
+
 	scs.onClusterLeaderChange()
 
 	return nil
@@ -220,6 +226,14 @@ func (scs *Service) pause() {
 	scs.server.Log().Debug("Shared Channel Service inactive")
 }
 
+// GetMemberSyncBatchSize returns the configured batch size for member synchronization
+func (scs *Service) GetMemberSyncBatchSize() int {
+	if scs.server.Config().ConnectedWorkspacesSettings.MemberSyncBatchSize != nil {
+		return *scs.server.Config().ConnectedWorkspacesSettings.MemberSyncBatchSize
+	}
+	return model.ConnectedWorkspacesSettingsDefaultMemberSyncBatchSize
+}
+
 // Makes the remote channel to be read-only(announcement mode, only admins can create posts and reactions).
 func (scs *Service) makeChannelReadOnly(channel *model.Channel) *model.AppError {
 	createPostPermission := model.ChannelModeratedPermissionsMap[model.PermissionCreatePost.Id]
@@ -314,17 +328,19 @@ func (scs *Service) scheduleGlobalUserSync(rc *model.RemoteCluster) {
 	}()
 }
 
-// OnReceiveSyncMessageForTesting exposes onReceiveSyncMessage for testing
-func (scs *Service) OnReceiveSyncMessageForTesting(msg model.RemoteClusterMsg, rc *model.RemoteCluster, response *remotecluster.Response) error {
-	return scs.onReceiveSyncMessage(msg, rc, response)
-}
-
-// GetUserSyncBatchSizeForTesting returns the configured batch size for user syncing (exported for testing)
-func (scs *Service) GetUserSyncBatchSizeForTesting() int {
-	return scs.getGlobalUserSyncBatchSize()
+// HasPendingTasksForTesting returns true if there are pending sync tasks in the queue
+func (scs *Service) HasPendingTasksForTesting() bool {
+	scs.mux.RLock()
+	defer scs.mux.RUnlock()
+	return len(scs.tasks) > 0
 }
 
 // HandleSyncAllUsersForTesting exposes syncAllUsers for testing
 func (scs *Service) HandleSyncAllUsersForTesting(rc *model.RemoteCluster) error {
 	return scs.syncAllUsers(rc)
 }
+
+// OnReceiveSyncMessageForTesting exposes onReceiveSyncMessage for testing
+func (scs *Service) OnReceiveSyncMessageForTesting(msg model.RemoteClusterMsg, rc *model.RemoteCluster, response *remotecluster.Response) error {
+	return scs.onReceiveSyncMessage(msg, rc, response)
+}

server/platform/services/sharedchannel/service_api.go

@@ -277,3 +277,41 @@ func (scs *Service) CheckCanInviteToSharedChannel(channelId string) error {
 	}
 	return nil
 }
+
+// updateMembershipSyncCursor updates the LastMembersSyncAt value for the shared channel remote
+// This provides centralized and consistent cursor management
+func (scs *Service) updateMembershipSyncCursor(channelID string, remoteID string, newTimestamp int64) error {
+	// Get the remote record
+	scr, err := scs.server.GetStore().SharedChannel().GetRemoteByIds(channelID, remoteID)
+	if err != nil {
+		scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to get shared channel remote for cursor update",
+			mlog.String("channel_id", channelID),
+			mlog.String("remote_id", remoteID),
+			mlog.Int("timestamp", int(newTimestamp)),
+			mlog.Err(err),
+		)
+		return fmt.Errorf("failed to get shared channel remote for cursor update: %w", err)
+	}
+
+	if scr == nil {
+		scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Shared channel remote not found for cursor update",
+			mlog.String("channel_id", channelID),
+			mlog.String("remote_id", remoteID),
+		)
+		return fmt.Errorf("shared channel remote not found for channel %s and remote %s", channelID, remoteID)
+	}
+
+	// Update the cursor - the store will handle ensuring it only moves forward
+	err = scs.server.GetStore().SharedChannel().UpdateRemoteMembershipCursor(scr.Id, newTimestamp)
+	if err != nil {
+		scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Failed to update membership cursor",
+			mlog.String("channel_id", channelID),
+			mlog.String("remote_id", remoteID),
+			mlog.String("remote_record_id", scr.Id),
+			mlog.Int("timestamp", int(newTimestamp)),
+			mlog.Err(err),
+		)
+	}
+
+	return err
+}

server/platform/services/sharedchannel/sync_recv.go

@@ -24,10 +24,9 @@ var (
 )
 
 func (scs *Service) onReceiveSyncMessage(msg model.RemoteClusterMsg, rc *model.RemoteCluster, response *remotecluster.Response) error {
-	if msg.Topic != TopicSync && msg.Topic != TopicGlobalUserSync {
-		return fmt.Errorf("wrong topic, expected `%s` or `%s`, got `%s`", TopicSync, TopicGlobalUserSync, msg.Topic)
+	if msg.Topic != TopicSync && msg.Topic != TopicChannelMembership && msg.Topic != TopicGlobalUserSync {
+		return fmt.Errorf("wrong topic, expected sync-related topic, got `%s`", msg.Topic)
 	}
-
 	if len(msg.Payload) == 0 {
 		return errors.New("empty sync message")
 	}
@@ -89,6 +88,15 @@ func (scs *Service) processSyncMessage(c request.CTX, syncMsg *model.SyncMsg, rc
 		ReactionErrors: make([]string, 0),
 	}
 
+	// Check if feature flag is enabled for membership changes
+	membershipSyncEnabled := scs.server.Config().FeatureFlags.EnableSharedChannelsMemberSync
+	hasMembershipChanges := len(syncMsg.MembershipChanges) > 0
+
+	// If this message only contains membership changes and feature is disabled, skip it
+	if hasMembershipChanges && !membershipSyncEnabled && len(syncMsg.Users) == 0 && len(syncMsg.Posts) == 0 && len(syncMsg.Reactions) == 0 {
+		return nil
+	}
+
 	scs.server.Log().Log(mlog.LvlSharedChannelServiceDebug, "Sync msg received",
 		mlog.String("remote", rc.Name),
 		mlog.String("channel_id", syncMsg.ChannelId),
@@ -96,6 +104,7 @@ func (scs *Service) processSyncMessage(c request.CTX, syncMsg *model.SyncMsg, rc
 		mlog.Int("post_count", len(syncMsg.Posts)),
 		mlog.Int("reaction_count", len(syncMsg.Reactions)),
 		mlog.Int("status_count", len(syncMsg.Statuses)),
+		mlog.Int("membership_change_count", len(syncMsg.MembershipChanges)),
 	)
 
 	// Check if this is a global user sync message (no channel ID and only users)
@@ -229,6 +238,19 @@ func (scs *Service) processSyncMessage(c request.CTX, syncMsg *model.SyncMsg, rc
 		scs.app.SaveAndBroadcastStatus(status)
 	}
 
+	// Process membership changes after users have been synced
+	if hasMembershipChanges && membershipSyncEnabled {
+		if err := scs.onReceiveMembershipChanges(syncMsg, rc, response); err != nil {
+			scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "Error processing membership changes",
+				mlog.String("remote", rc.Name),
+				mlog.String("channel_id", syncMsg.ChannelId),
+				mlog.Int("change_count", len(syncMsg.MembershipChanges)),
+				mlog.Err(err),
+			)
+			// Don't fail the entire sync if membership changes fail
+		}
+	}
+
 	response.SetPayload(syncResp)
 
 	return nil

server/platform/services/sharedchannel/sync_send.go

@@ -37,8 +37,17 @@ func newSyncTask(channelID, userID string, remoteID string, existingMsg, retryMs
 		retryID = retryMsg.Id
 	}
 
+	// Generate a unique task ID
+	taskID := channelID + userID + remoteID + retryID // combination of ids to avoid duplicates
+
+	// For batch tasks, add a batch identifier to make the ID unique
+	if existingMsg != nil && len(existingMsg.MembershipChanges) > 1 {
+		batchID := model.NewId()[:8] // Use a short unique ID for the batch
+		taskID = channelID + "batch" + batchID + remoteID + retryID
+	}
+
 	return syncTask{
-		id:          channelID + userID + remoteID + retryID, // combination of ids to avoid duplicates
+		id:          taskID,
 		channelID:   channelID,
 		userID:      userID,
 		remoteID:    remoteID, // empty means update all remote clusters
@@ -235,6 +244,7 @@ func (scs *Service) ForceSyncForRemote(rc *model.RemoteCluster) {
 // addTask adds or re-adds a task to the queue.
 func (scs *Service) addTask(task syncTask) {
 	task.AddedAt = time.Now()
+
 	scs.mux.Lock()
 	if originalTask, ok := scs.tasks[task.id]; ok {
 		// if the task was already scheduled, we only update the
@@ -365,6 +375,16 @@ func (scs *Service) removeOldestTask() (syncTask, bool, time.Duration) {
 
 // processTask updates one or more remote clusters with any new channel content.
 func (scs *Service) processTask(task syncTask) error {
+	// Check if this is a membership change task
+	if task.existingMsg != nil && len(task.existingMsg.MembershipChanges) > 0 {
+		// Check if feature flag is enabled
+		if !scs.server.Config().FeatureFlags.EnableSharedChannelsMemberSync {
+			return nil
+		}
+		scs.processMembershipChange(task.existingMsg)
+		return nil
+	}
+
 	// map is used to ensure remotes don't get sync'd twice, such as when
 	// they have the autoinvited flag and have explicitly subscribed to a channel.
 	remotesMap := make(map[string]*model.RemoteCluster)

server/platform/services/sharedchannel/sync_send_remote.go

@@ -119,6 +119,7 @@ func (scs *Service) syncForRemote(task syncTask, rc *model.RemoteCluster) error
 			RemoteId:          rc.RemoteId,
 			LastPostCreateAt:  model.GetMillis(),
 			LastPostUpdateAt:  model.GetMillis(),
+			LastMembersSyncAt: 0,
 		}
 		if scr, err = scs.server.GetStore().SharedChannel().SaveRemote(scr); err != nil {
 			return fmt.Errorf("cannot auto-create shared channel remote (channel_id=%s, remote_id=%s): %w", task.channelID, rc.RemoteId, err)

server/public/model/channel.go

@@ -507,3 +507,15 @@ type GroupMessageConversionRequestBody struct {
 	Name        string `json:"name"`
 	DisplayName string `json:"display_name"`
 }
+
+// ChannelMembersGetOptions provides parameters for getting channel members
+type ChannelMembersGetOptions struct {
+	// ChannelID specifies which channel to get members for
+	ChannelID string
+	// Offset for pagination
+	Offset int
+	// Limit for pagination (maximum number of results to return)
+	Limit int
+	// UpdatedAfter filters members updated after the given timestamp (cursor-based pagination)
+	UpdatedAfter int64
+}

server/public/model/config.go

@@ -49,7 +49,8 @@ const (
 	PasswordMaximumLength = 72
 	PasswordMinimumLength = 5
 
-	ServiceGitlab    = "gitlab"
+	ServiceGitlab = "gitlab"
+
 	ServiceGoogle    = "google"
 	ServiceOffice365 = "office365"
 	ServiceOpenid    = "openid"
@@ -285,7 +286,8 @@ const (
 
 	LocalModeSocketPath = "/var/tmp/mattermost_local.socket"
 
-	ConnectedWorkspacesSettingsDefaultMaxPostsPerSync = 50 // a bit more than 4 typical screenfulls of posts
+	ConnectedWorkspacesSettingsDefaultMaxPostsPerSync     = 50 // a bit more than 4 typical screenfulls of posts
+	ConnectedWorkspacesSettingsDefaultMemberSyncBatchSize = 20 // optimal batch size for syncing channel members
 
 	// These storage classes are the valid values for the x-amz-storage-class header. More documentation here https://docs.aws.amazon.com/AmazonS3/latest/API/API_PutObject.html#AmazonS3-PutObject-request-header-StorageClass
 	StorageClassStandard           = "STANDARD"
@@ -3462,6 +3464,7 @@ type ConnectedWorkspacesSettings struct {
 	SyncUsersOnConnectionOpen       *bool
 	GlobalUserSyncBatchSize         *int
 	MaxPostsPerSync                 *int
+	MemberSyncBatchSize             *int // Maximum number of members to process in a single batch during shared channel synchronization
 }
 
 func (c *ConnectedWorkspacesSettings) SetDefaults(isUpdate bool, e ExperimentalSettings) {
@@ -3496,6 +3499,10 @@ func (c *ConnectedWorkspacesSettings) SetDefaults(isUpdate bool, e ExperimentalS
 	if c.MaxPostsPerSync == nil {
 		c.MaxPostsPerSync = NewPointer(ConnectedWorkspacesSettingsDefaultMaxPostsPerSync)
 	}
+
+	if c.MemberSyncBatchSize == nil {
+		c.MemberSyncBatchSize = NewPointer(ConnectedWorkspacesSettingsDefaultMemberSyncBatchSize)
+	}
 }
 
 type GlobalRelayMessageExportSettings struct {

server/public/model/feature_flags.go

@@ -25,6 +25,9 @@ type FeatureFlags struct {
 	// Enable plugins in shared channels.
 	EnableSharedChannelsPlugins bool
 
+	// Enable synchronization of channel members in shared channels
+	EnableSharedChannelsMemberSync bool
+
 	// Enable syncing all users for remote clusters in shared channels
 	EnableSyncAllUsersForRemoteCluster bool
 
@@ -72,6 +75,7 @@ func (f *FeatureFlags) SetDefaults() {
 	f.TestBoolFeature = false
 	f.EnableRemoteClusterService = false
 	f.EnableSharedChannelsDMs = false
+	f.EnableSharedChannelsMemberSync = false
 	f.EnableSyncAllUsersForRemoteCluster = false
 	f.EnableSharedChannelsPlugins = true
 	f.AppsEnabled = false

server/public/model/shared_channel.go

@@ -118,6 +118,7 @@ type SharedChannelRemote struct {
 	LastPostUpdateID  string `json:"last_post_id"`
 	LastPostCreateAt  int64  `json:"last_post_create_at"`
 	LastPostCreateID  string `json:"last_post_create_id"`
+	LastMembersSyncAt int64  `json:"last_members_sync_at"`
 }
 
 func (sc *SharedChannelRemote) IsValid() *AppError {
@@ -169,12 +170,13 @@ type SharedChannelRemoteStatus struct {
 // SharedChannelUser stores a lastSyncAt timestamp on behalf of a remote cluster for
 // each user that has been synchronized.
 type SharedChannelUser struct {
-	Id         string `json:"id"`
-	UserId     string `json:"user_id"`
-	ChannelId  string `json:"channel_id"`
-	RemoteId   string `json:"remote_id"`
-	CreateAt   int64  `json:"create_at"`
-	LastSyncAt int64  `json:"last_sync_at"`
+	Id                   string `json:"id"`
+	UserId               string `json:"user_id"`
+	ChannelId            string `json:"channel_id"`
+	RemoteId             string `json:"remote_id"`
+	CreateAt             int64  `json:"create_at"`
+	LastSyncAt           int64  `json:"last_sync_at"`
+	LastMembershipSyncAt int64  `json:"last_membership_sync_at"`
 }
 
 func (scu *SharedChannelUser) PreSave() {
@@ -270,15 +272,25 @@ type SharedChannelRemoteFilterOpts struct {
 	IncludeDeleted     bool
 }
 
+// MembershipChangeMsg represents a change in channel membership
+type MembershipChangeMsg struct {
+	ChannelId  string `json:"channel_id"`
+	UserId     string `json:"user_id"`
+	IsAdd      bool   `json:"is_add"`
+	RemoteId   string `json:"remote_id"`
+	ChangeTime int64  `json:"change_time"`
+}
+
 // SyncMsg represents a change in content (post add/edit/delete, reaction add/remove, users).
 // It is sent to remote clusters as the payload of a `RemoteClusterMsg`.
 type SyncMsg struct {
-	Id        string           `json:"id"`
-	ChannelId string           `json:"channel_id"`
-	Users     map[string]*User `json:"users,omitempty"`
-	Posts     []*Post          `json:"posts,omitempty"`
-	Reactions []*Reaction      `json:"reactions,omitempty"`
-	Statuses  []*Status        `json:"statuses,omitempty"`
+	Id                string                 `json:"id"`
+	ChannelId         string                 `json:"channel_id"`
+	Users             map[string]*User       `json:"users,omitempty"`
+	Posts             []*Post                `json:"posts,omitempty"`
+	Reactions         []*Reaction            `json:"reactions,omitempty"`
+	Statuses          []*Status              `json:"statuses,omitempty"`
+	MembershipChanges []*MembershipChangeMsg `json:"membership_changes,omitempty"`
 }
 
 func NewSyncMsg(channelID string) *SyncMsg {