Neither the XSync nor the windows backend explicitly call resumingFromIdle in simulateUserActivity, so I think this should be fine.
However, I don't know if that won't indirectly trigger it if the session was idle? Maybe we need to check if the session was idle and only then emit the signal.
I'm not sure how exactly it works, but if session was idle, wouldn't function screensaverActivated be called on changing state? And it contains emit resumingFromIdle():