Longerekel:”It is certainly pagum in the original cup and cannot be used another time as a kos shel bracha”
How and when is your writing relevent? If one needs a “kos sholem” for the next kos shel brocho, anyway one has to add more wine or water and therefore it isn’t pagum any longer. If you wish to use a heiche timtze that he puts into the cup a whole unpeeled egg to bring it into a kos sholem, how do you know in the same cup it is certainly pagum with the subsequent brocho.
“It is not pagum with regard to the original bracha, only with regard to a subsequent bracha”
Question: If a second person who was not yotzei with the mevurech’s brocho, can he make his own brocho and the drinking will or will not be kos pagum (since it is a “subsequent brocho”) .