Mixed-role clients in federated LLM unlearning

Extend FIRM to federated clients that simultaneously hold deletion-requested data and retained data, allowing a single client to contribute both forget and retain information for the same request.

Background

The current FIRM protocol assigns each client a single role for a given request: either providing a forget update or providing a retain summary. The authors leave unresolved the extension to clients whose private datasets contain both information that must be deleted and information that must be preserved.