Interesting... I agree that when referring to an action, contraction is rare. But when the action is distanced (so that it's not an action really, but a reference to the action) contraction is possible.
Example:
When can we meet?
Any time really, except...[looking at diary] .. except Monday, when I've lunch'
Or... not sure
... perhaps you'd normally use a noun here - I've a lunch/a meeting/an appointment... :?:
b