fix: add groupExistenceBatchReader interface and update test stub for release branch compatibility

backend/internal/service/admin_service.go

@@ -336,6 +336,10 @@ type ProxyExitInfoProber interface {
 	ProbeProxy(ctx context.Context, proxyURL string) (*ProxyExitInfo, int64, error)
 }
 
+type groupExistenceBatchReader interface {
+	ExistsByIDs(ctx context.Context, ids []int64) (map[int64]bool, error)
+}
+
 type proxyQualityTarget struct {
 	Target          string
 	URL             string

backend/internal/service/admin_service_bulk_update_test.go

@@ -15,6 +15,7 @@ type accountRepoStubForBulkUpdate struct {
 	bulkUpdateErr    error
 	bulkUpdateIDs    []int64
 	bindGroupErrByID map[int64]error
+	bindGroupsCalls  []int64
 	getByIDsAccounts []*Account
 	getByIDsErr      error
 	getByIDsCalled   bool
@@ -22,6 +23,8 @@ type accountRepoStubForBulkUpdate struct {
 	getByIDAccounts  map[int64]*Account
 	getByIDErrByID   map[int64]error
 	getByIDCalled    []int64
+	listByGroupData  map[int64][]Account
+	listByGroupErr   map[int64]error
 }
 
 func (s *accountRepoStubForBulkUpdate) BulkUpdate(_ context.Context, ids []int64, _ AccountBulkUpdate) (int64, error) {
@@ -33,12 +36,23 @@ func (s *accountRepoStubForBulkUpdate) BulkUpdate(_ context.Context, ids []int64
 }
 
 func (s *accountRepoStubForBulkUpdate) BindGroups(_ context.Context, accountID int64, _ []int64) error {
+	s.bindGroupsCalls = append(s.bindGroupsCalls, accountID)
 	if err, ok := s.bindGroupErrByID[accountID]; ok {
 		return err
 	}
 	return nil
 }
 
+func (s *accountRepoStubForBulkUpdate) ListByGroup(_ context.Context, groupID int64) ([]Account, error) {
+	if err, ok := s.listByGroupErr[groupID]; ok {
+		return nil, err
+	}
+	if rows, ok := s.listByGroupData[groupID]; ok {
+		return rows, nil
+	}
+	return nil, nil
+}
+
 func (s *accountRepoStubForBulkUpdate) GetByIDs(_ context.Context, ids []int64) ([]*Account, error) {
 	s.getByIDsCalled = true
 	s.getByIDsIDs = append([]int64{}, ids...)
@@ -106,22 +120,6 @@ func TestAdminService_BulkUpdateAccounts_PartialFailureIDs(t *testing.T) {
 	require.Len(t, result.Results, 3)
 }
 
-func TestAdminService_BulkUpdateAccounts_NilGroupRepoReturnsError(t *testing.T) {
-	repo := &accountRepoStubForBulkUpdate{}
-	svc := &adminServiceImpl{accountRepo: repo}
-
-	groupIDs := []int64{10}
-	input := &BulkUpdateAccountsInput{
-		AccountIDs: []int64{1},
-		GroupIDs:   &groupIDs,
-	}
-
-	result, err := svc.BulkUpdateAccounts(context.Background(), input)
-	require.Nil(t, result)
-	require.Error(t, err)
-	require.Contains(t, err.Error(), "group repository not configured")
-}
-
 // TestAdminService_BulkUpdateAccounts_MixedChannelPreCheckBlocksOnExistingConflict verifies
 // that the global pre-check detects a conflict with existing group members and returns an
 // error before any DB write is performed.