I ended up implementing this in JavaScript using Rx, but the core concept is the same:

    Incoming requests:     --a------------->
    Requests to server:    ---b------------>
    Responses from server: -----------d---->
    Updates to app state:  ---c--------e--->

a - User "sends message" to chat room

b - Handler for that action queues a request

c - Handler for that action also queues a local update

d - Server responds with the sent message

e - Handler for that response queues a local update