fix: harden explore dataset collection

backend/internal/logic/dataset/handlers_test.go

@@ -38,6 +38,10 @@ func TestDatasetAPIConnectsSourcesItemsAndSyncTasks(t *testing.T) {
 	require.NotEmpty(t, source.ID)
 	require.Equal(t, "Industry feed", source.Name)
 	require.Empty(t, source.IconURL)
+	var storedSource models.SaDatasetSource
+	require.NoError(t, database.Where("identity = ?", source.ID).First(&storedSource).Error)
+	require.Equal(t, owner.ID, storedSource.CreatedBy)
+	require.Equal(t, owner.Identity, storedSource.CreatedByIdentity)
 
 	createdItem := performDatasetRequest(t, ownerRouter, http.MethodPost, "/api/v1/dataset-items", map[string]any{
 		"sourceId": source.ID, "title": "A collected article", "summary": "Summary",
@@ -108,6 +112,10 @@ func newDatasetTestDatabase(t *testing.T) *gorm.DB {
 		&models.SaDatasetItem{},
 		&models.SaDatasetCron{},
 	))
+	require.NoError(t, database.Exec(`
+		CREATE UNIQUE INDEX idx_sa_dataset_item_source_external
+		ON sa_dataset_items (source_id, external_id)
+	`).Error)
 	return database
 }