@integralexplorer you have a typo in your conversions: it should be :glitter-index instead of :glitter-dex. I've found it by adding println to the convert function:

(defn convert
  [vamp-key value]
  (println "convert:" vamp-key " -- " value)
  ((get conversions vamp-key) value))

Thank you. Such a simple thing and such time spent wandering in the cloud of unknowing. Even though I looked at all the code several times, focusing in on, the areas I thought were an issue, I did not see my mistake. I have now learned the importance of really checking the code in places that don't seem to be a problem and also to use println actively. I will pay attention and begin to figure out the approach to its use. And I am properly humbled by the little pebble that tripped me up. I am now back to Brave and True.

Initially, I thought that problem was in some nil passed to str->int function but a quick REPL experiment revealed the error

Yes, that is what I thought as well but was quite uncertain leading down many paths of research. You just also helped me by reminding me that the REPL is my friend and should be the first place to experiment. These are important experiences to learn for a newbie and the gift from someone who knows. Thanks again.