Reuse document indexes in D&D validators

internal/modules/dnd/validate/scenedescriptions/source_refs/validator.go

@@ -42,9 +42,10 @@ func (v *Validator) Validate(_ context.Context, req contracts.TypedValidationReq
 	if req.Stage == string(pipeline.StageExtract) && req.Chunk == nil {
 		issues = append(issues, "current extraction chunk must not be nil")
 	}
-	for index, scene := range req.Value.Scenes {
-		prefix := fmt.Sprintf("scenes[%d]", index)
-		if err := source.ValidateRef(req.Source, scene.SourceRef); err != nil {
+	index := source.NewDocumentIndex(req.Source)
+	for sceneIndex, scene := range req.Value.Scenes {
+		prefix := fmt.Sprintf("scenes[%d]", sceneIndex)
+		if err := index.ValidateRef(scene.SourceRef); err != nil {
 			issues = append(issues, prefix+".source_ref: "+diagnostics.Truncate(err.Error()))
 			continue
 		}