In the demo in https://github.com/microsoft/vscode-internalbacklog/issues/2178#issuecomment-901514989, I had to manually create a file in the web workspace since I couldn't figure out a way to get vscode.window.showOpenDialog to open a file on the user's machine. Rob suggested that adding a file:/// URI as the defaultUri might work, but it doesn't.

Is opening a local file in this way already possible, and if not could we add a way for it to happen, perhaps using the defaultUri as Rob suggested?