As I'm trying to implement the R Notebook using the Notebook API at #394 initiated by #378, I have no clue at the moment how to make language server work when editing R code cells.
The notebook API introduces a new schema vscode-notebook-cell which is not covered by the document selector of the language client created in vscode-r-lsp. I'm not sure if anything has to be changed in languageserver and vscode-r-lsp to handle requests from a notebook or notebook cell.