This is really a question, more than a claim that the code is wrong. I'm trying to understand middleware descriptors and the example for "add-stdin" isn't making sense to me with respect to the key path '[:handles "stdin" :returns]' which points to a string describing a possible status:

https://github.com/clojure/tools.nrepl/blob/fcac1e13d6f80eb0db28773247a769c1dc9659b1/src/main/clojure/clojure/tools/nrepl/middleware/session.clj#L247

I can't figure out how this middleware could do that, given the only mention is in the function "session-in", which is only seemingly reachable from the "session" middleware.