fix: harden exploration data flow

backend/internal/logic/dataset/handlers_test.go

@@ -93,6 +93,7 @@ func TestDatasetAPIConnectsSourcesItemsAndSyncTasks(t *testing.T) {
 	var depositedNote models.SaNote
 	require.NoError(t, database.Where("project_id = ?", project.ID).First(&depositedNote).Error)
 	require.Equal(t, item.Title, depositedNote.Title)
+	require.Contains(t, depositedNote.Markdown, "![文章图片](https://example.com/article.jpg)")
 	require.Contains(t, depositedNote.Markdown, "原文链接")
 
 	firstSync := performDatasetRequest(t, ownerRouter, http.MethodPost, "/api/v1/dataset-sources/sync", map[string]any{})
@@ -237,10 +238,6 @@ func newDatasetTestDatabase(t *testing.T) *gorm.DB {
 		&models.SaProject{},
 		&models.SaNote{},
 	))
-	require.NoError(t, database.Exec(`
-		CREATE UNIQUE INDEX IF NOT EXISTS idx_sa_dataset_item_source_external
-		ON sa_dataset_items (source_id, external_id)
-	`).Error)
 	return database
 }