Incompatible with `ggplot2` or is it a plot device issue I don't understand?

The following model code

extensions [ sr ]

to setup
  clear-all
  sr:setup
  sr:run "library(ggplot2)"
end

to ggplot
  sr:set-plot-device
  (sr:run
    "df <- data.frame(x = rnorm(30), y = rnorm(30))"
    "ggplot(df) + "
    "  geom_point(aes(x = x, y = y))"
  )
  sr:run "ggsave('~/Downloads/test.png')"
  user-message "Plot will close when you close this dialog."
  sr:run "dev.off()"
end  

fails to show a plot in the on-screen plot window, although the expected ggplot shows up as the requested PNG file:

The user-message is my way to cleanly close plot devices - so don't worry about that part.

Is this some subtlety or R plotting, specifically in relation to ggplot that I don't understand? Or is it a problem with the Simple R extension? How do I do I to get an on-screen ggplot to show up?

Start by reproducing the model using sr:set-plot-device, sr:run, ggplot, ggsave, and dev.off(), comparing the on-screen plot window with the generated PNG. Investigate whether the Simple R extension supports displaying the ggplot device and define done as an on-screen ggplot appearing while the existing PNG behavior remains correct.