[hlx6] copy+paste document in the same directory doesn't work

**This issue applies only to running with the Helix 6 backend.**

Take a document in a folder, that has some content in it.

Copy it and paste it back into the same folder.

A new document appears with the name `doc-copy`. Open it and see that it doesn't exist yet.

On further inspection, the document seems to have been copied to the wrong place, as a new folder /org/site/org/site/folder/doc-copy has appeared (note the duplication of org/site).

See this video for a demonstration:

https://github.com/user-attachments/assets/2785bfd3-e88f-4cf8-9006-479d17ed7980