> (Notice how this has no separation about "filenames" and "data")
Notice how it doesn't say _anything_ at all about the content of the file _on_ _disk_ that is being renamed into the old file. That is because in order to see the file _durably_, you have to commit its content. Completely unrelated to committing the _rename_.
Just because another process can see the link (and access the data correctly, which may still just be cached by the kernel) does _not_ mean data reached the disk yet.
BTW, thanks for working on fixes of this in Gnome.