is (doto (a/chan) (a/close!)) the correct way to create a port that drops every input?

I believe that would close the channel, and make it inoperable

you need some sort of buffer that drops values

https://clojuredocs.org/clojure.core.async/sliding-buffer

(chan (sliding-buffer 1)) is probably what you want

you can also use an ordinary channel, with or without a buffer and launch a go block that sinks the value before handing back the channel to the producer

If the client never checks the return value of a put, a closed chan acts like a chan that drops ever input. IIRC even a promise-chan would actually (it would set itself from the first value, and consume and ignore the rest).

a dev-null-chan seems like a potentially useful feature though

I went ahead and made a dev null buffer 😛

it never blocks, takes always get nil, and puts always return true

it's Universe Scale!