Deep-clone source metadata during chunk materialization

internal/core/source/chunk_plan.go

@@ -162,7 +162,10 @@ func MaterializeChunkPlan(doc *SourceDocument, plan ChunkPlan) ([]Chunk, error)
 	for index, chunkRange := range plan.Ranges {
 		start, _ := UnitIndex(doc, chunkRange.StartUnitID)
 		end, _ := UnitIndex(doc, chunkRange.EndUnitID)
-		units := cloneSourceUnits(doc.Units[start : end+1])
+		units, err := cloneSourceUnits(doc.Units[start : end+1])
+		if err != nil {
+			return nil, fmt.Errorf("clone chunk plan range[%d] units: %w", index, err)
+		}
 		content, err := json.Marshal(struct {
 			Units []SourceUnit `json:"units"`
 		}{Units: units})
@@ -189,52 +192,18 @@ func MaterializeChunkPlan(doc *SourceDocument, plan ChunkPlan) ([]Chunk, error)
 	return chunks, nil
 }
 
-func cloneSourceUnits(units []SourceUnit) []SourceUnit {
+func cloneSourceUnits(units []SourceUnit) ([]SourceUnit, error) {
 	if len(units) == 0 {
-		return nil
+		return nil, nil
 	}
 	cloned := make([]SourceUnit, len(units))
 	for i, unit := range units {
 		cloned[i] = unit
-		cloned[i].Metadata = cloneJSONMap(unit.Metadata)
-	}
-	return cloned
-}
-
-func cloneJSONMap(values map[string]any) map[string]any {
-	if len(values) == 0 {
-		return nil
-	}
-	cloned := make(map[string]any, len(values))
-	for key, value := range values {
-		cloned[key] = cloneJSONValue(value)
-	}
-	return cloned
-}
-
-func cloneJSONValue(value any) any {
-	switch typed := value.(type) {
-	case map[string]any:
-		return cloneJSONMap(typed)
-	case []any:
-		cloned := make([]any, len(typed))
-		for i := range typed {
-			cloned[i] = cloneJSONValue(typed[i])
+		metadata, err := CloneMetadata(unit.Metadata)
+		if err != nil {
+			return nil, fmt.Errorf("source unit[%d] metadata: %w", i, err)
 		}
-		return cloned
-	case json.RawMessage:
-		return append(json.RawMessage(nil), typed...)
-	case []byte:
-		return append([]byte(nil), typed...)
-	case []string:
-		return append([]string(nil), typed...)
-	case map[string]string:
-		cloned := make(map[string]string, len(typed))
-		for key, item := range typed {
-			cloned[key] = item
-		}
-		return cloned
-	default:
-		return value
+		cloned[i].Metadata = metadata
 	}
+	return cloned, nil
 }