How can platform-independent libraries depend on the client?

I'm opening this issue in response to this comment:

Due to the architectural changes leading the lib not to be isomorphic anymore, this is no longer relevant.

We have a couple of JavaScript libraries that will use this client in order to interface with Solid pods. Some of those libraries can run either on the client (browser, native, …), the server (Node.js, …), or an intermediary (Node.js, …). Concretely, I'm thinking about libraries such as:

• rdflib.js
• Comunica
• LDflex
• …

These libraries, which themselves do not commit to a platform, need to depend on a generic notion of a Solid client.
Only when these libraries are used by a concrete application, they will be bound to a concrete platform by that application.

If not via isomorphism, how are we going to achieve this?
Very concretely, what do I as a builder of platform-agnostic Solid libraries put in my package.json?