(I am a VIM-n00b)
According to the VCSCommand docs, the commands will operate on a directory if you are currently in a “directory buffer”. I can’t seem to find any other references to opening a “directory buffer” though.
What am I (probably very stupidly) missing?
Looks like it is buffer with
filetype=netrw: if you open a directory in vim (for example, tryvim .), it will usenetrwplugin which is distributed with the official package.