Finalizers, proxy and two-way communication

[Nemikolh]

proxyCounter for an endpoint should at least be incremented by 1 when Comlink.expose is called on that endpoint. Otherwise things might break if a proxy is temporarily created to call a function despite a Comlink.expose being active.

Reproducible example: https://stackblitz.com/edit/node-afa7lv?file=index.html