Don't worry about it. One of the big advantages of them foraging for their own food is that your feed bill goes down. They'll soon eat the quality forage in an enclosed run and go back to depending more on the feed.
A couple of things to watch for. If your egg shells start to get thin, that means they are not getting enough calcium in their forage. There is calcium in forage. Wild birds get enough calcium to make their egg shells, even those that eat mostly grain. Chickens have foraged for their food in free range situations for thousands of years and done fine without any supplemental feeding, but that depends on the quality of their forage. Sometimes they do need supplements. Each if us have different situations. Your Layer has enough calcium in it for the egg shells if Layer is all they eat, but if they are eating a lot of forage, they may not be getting enough calcium. You might want to offer oyster shell on the side as a preventative. And if you notice the egg shells getting thin, I'd certainly offer oyster shell or some other calcium source.
Another thing you might see is that the eggs get a bit smaller. If the amount of protein they are getting in the forage drops, the eggs can get smaller. The amount of protein they eat helps determine egg size. To me, that is not a big deal. I can live with the eggs being a bit smaller if my feed bill is less. You can counter that a bit by offering high protein treats, but I'd not overdo it to try to get really large eggs. If a hen tries to lay really large eggs she is a little more likely to have medical problems. Not that each and every one will, just that they are a litlle more likely.
I personally consider your situation a good thing, but since they are in an enclosed run, it is only temporary. They will soon eat the quality forage.
