"Cups of gold and wine"

It’s an instance of syllepsis, in which 'one word is used with two senses in the same utterance’ (Katie Wales, ‘A Dictionary of Stylistics’)

Another name for this device is 'zeugma'.

As to the question of whether both phrases are examples of syllepsis/zeugma...is the jury in or out? I'm not sure. Both of the parallel statements in the 'cups' quotation are literal; textbook examples of zeugma involve a mix of literal and figurative language. As in, 'he took his leave and his coat'. (Can't think of a more interesting example off the top of my head.)

Similarly, the words 'I am' do the same job whether used in the sentence 'I am silver' and 'I am exact'.

'A mirror silver and exact' -- suddenly sounds a lot like zeugma...

Perhaps we can describe these as examples of weak zeugma, or avoid trying to pin a label to them altogether and, instead, note the parallel construction.

I like how the Plath quotation is self-referential. In that it seems overly exact to add the words 'and exact' to the description