Expose chunk plan provenance and safe diagnostics

internal/modules/generic/output/json/encoder.go

@@ -273,11 +273,32 @@ func cloneMetadata(metadata map[string]any) map[string]any {
 	}
 	out := make(map[string]any, len(metadata))
 	for key, value := range metadata {
-		out[key] = value
+		out[key] = cloneJSONMetadataValue(value)
 	}
 	return out
 }
 
+func cloneJSONMetadataValue(value any) any {
+	switch typed := value.(type) {
+	case map[string]any:
+		return cloneMetadata(typed)
+	case []any:
+		out := make([]any, len(typed))
+		for i := range typed {
+			out[i] = cloneJSONMetadataValue(typed[i])
+		}
+		return out
+	case stdjson.RawMessage:
+		return append(stdjson.RawMessage(nil), typed...)
+	case []byte:
+		return append([]byte(nil), typed...)
+	case []string:
+		return append([]string(nil), typed...)
+	default:
+		return value
+	}
+}
+
 func encoderErrorf(format string, args ...any) error {
 	return fmt.Errorf("json output encoder: "+format, args...)
 }