On 2022-12-23 3:28 AM, Thomas Corthals wrote: ...
If your schema is configured correctly for atomic updates, you can add child documents atomically as well.
So the answer was to make _root_ stored and docValues = true, and to delete _text_ that was there w/o the corresp. copyField by default. After that adding child documents works as described in https://solr.apache.org/guide/8_11/updating-parts-of-documents.html
Thanks for the hints, Dima