you can set the repeat mode to none, but then you can trigger it to
restart (at least I cant find a published input for that). How do
you get an LFO to spit out just one cycle (ie triggered by a
keypress)?
You can try to set the timebase of the LFO to "External" through the
contextual menu, then connect a Math patch to it with a single
operation Min(1, x), where x comes from a Stop Watch patch, triggered
by the key press.
So you press a key, it starts the clock which goes from 0 to 1 only
because of the Min() operation and drives the LFO time. Note that
the LFO must have a period value set to 1 as well.