Shopping cart experience across two sales channels

we’re looking for a solution to enable a unified shopping cart experience across two sales channels: firstSalesChannel.de and secondSalesChannel.de. Both channels offer similar products. If a customer adds a product to their cart on firstSalesChannel.de but doesn’t complete the order, and then visits secondSalesChannel.de, we want the same products to be automatically added to the cart if available on the second channel. How can we achieve this?