Somewhere in their business logic there would probably be a cutoff where board orders of a certain stackup go to a different factory and result in longer lead times, but I didn’t dig too deep into the options to find out what those cutoffs were. After uploading gerbers during the order...
So it's hopeless as a current-sense resistor (where the small resistances might prove useful) in switching circuits.Or did you mean embedded components as in carbon ink, chips embedded in the stackup, etc.? Which are also possible -- but I can't imagine a proto fab doing such esoterica...