Andreas Ericsson [off-list ref] writes:
How about "git update-index --undo path...", possibly with "git reset
path..." as a shorthand.
While "git reset path..." may make sense, "update-index --undo"
does not make any sense from the core point of view. That
command is about interaction between index and working tree file
and does not know anything about "the last commit", "the current
head commit", nor tree objects in general, so it does not know
where to get the undo information from.
I'll find time to code a prototype for "git reset path..." up
unless somebody beats me to it.