The term you're looking for is "surplus". The consumer sees a surplus of value because the price they paid is below the maximum they're willing to pay, and the producer sees a surplus because the price they charged was more than the cost to produce the good. In this economic system both parties benefit. Economic surplus is the thing that is "created" with every transaction. "Surplus accumulation" as a concept doesn't make any sense, and is isomorphic to what you think people are saying when they use the phrase "wealth accumulation." You should update your definition of "wealth".

What's your definition of wealth?