Hi,
org-roam use file node, but this design losses some convenience of headline, such as toggle TODO status and handy way to add or change priority, check box etc. It also make the logic of org-roam-extract-subtree complex, see issues like this one. And by the way the file node seems ugly to me, not as clean as a headline.
So, why not replace the file node with a file that only have one headline?