1. My hand contains a Workshop and a Sheepdog.
2. I play the Workshop and gain a card.
3. I react with the Sheepdog, drawing two more cards.
4. One of the cards I draw is a Sheepdog
Can I react with the second Sheepdog? Right now, the online game allows me to, but it seems strange to me that I can react to an event with a card I did not have in my hand at the time of the event.
I agree with you that it doesn't feel very natural, but it is correct according to the dominion rules.
The thought behind this rule is/was that your opponents can't know if you already had the Sheepdogs in hand.
That is correct. Think of it as still being in this time window where you have gained a card and are reacting to it.
(Otherwise you could also not prove that you already had both Sheepdogs in hand, if that was the case,)
Thanks for the feedback, y'all! You've sent my mind at ease.