dash: Event.uniqueRate does not check whether the removed content was already cached (future over-credit) #587

Event.uniqueRate prices a first removal at the cache-write rate for every component except the summarizers. That is right for extract_llm and extract_llm_sweep today: they act on output that arrives in the same turn, or on a cold turn. A future component that removes content an earlier turn already cached would be over-credited at the write rate instead of the read rate.

Fix: price a first removal from whether the removed content sat in a cache entry that was live on the previous turn (the verdict #546 uses for summaries), not from the component name. Add a test with a non-summarizer that removes earlier transcript. Related: #546, #573.