Thank you for the solution, which works for me.
While I see what the code does, I don’t really understand the different working of #let dropcap = orig-dropcap.with() compared to #let dropcap(body) = orig-dropcap().
As for transform: it => it.trim(), I am completely in the dark with that!
Finally, while some graphic design guru(s) may consider the dropcap including the space as acceptable, I find them exceedingly ugly and to me they stand out like a sore thumb against the other non-spaced dropcaps.
I shall now (when I have time, that is) experiment to see if one could, on the basis of this code, use a decorated font for the dropcaps à la mediaeval manuscript.
Mark