The HttpClient class level java doc has an API note about closing a client and reclaiming resource. There should also be an implementation note documenting what happens when a client is garbage collected without being explicitly closed.

In particular, it may not be obvious that an InputStream always need to be closed, which requires to always call HttpResponse::body() when the body is an InputStream.

At a minimum, the various BodyHandlers and BodySubscriber whose body need to be closed should link to the API/implementation note in the HttpClient class level documentation.