If two authors collaborate, and each of them already has an agent - then who handles the collaborative work?
Do the authors decide to be jointly represented under one of their two agents? If that's the case, doesn't that "cut out" the other agent - barring them from a major project of an author they represent? Or is their some type of agreement which will let both agents in on the project? Alternatively, should the two consider finding a third agent to handle their collaborative work?
And finally, what if one of the authors has an agent, and the other doesn't? Should the unagented author accept their co-writer's agent, or not necessarily?
Obviously, different cases should be handled differently, and choosing an agent is a joint decision the two authors make like any other - with consideration and cooperation. However, I would like to understand both common practice and important considerations for the choice.