>I get that automation significantly reduces the labor time necessary to produce a commodity
It's not only about the cost of a commodity. Transactions are not free, you have to spend time interacting with a transaction system like money tokens, credit cards and labour vouchers too. You have to spend mental energy to decide on purchases. At some point the hole of humanity would spend more time and effort on transactions than they work in the economy it self. It just becomes overhead.
>but won’t a few job sectors like construction, resource extraction like mining, wholesale and retail distribution always add a significant number of hours of labor time per person to the commodity?
I don't really know how the future looks like but replicators don't have much in terms of externalities, they need power, and maybe once in a while you need to refill the matter cartridge because it doesn't perfectly recycle. The replicator is just a projection of observable trends, like productivity improving, and shrinking of the size of production tools relative to the products they make, and it's the ultimate multi tool, because in principle it could do any modification you want. I don't really know what people will do, basically all the constrains we have today would be removed. If i want to make a prediction i'm left with few indicators, but there definitely is a lower cut-off point where prices make no sense to humans. And that's what i'm basing this on.