Multi-device support in an encrypted messenger is an authorization problem. It is not a sync problem, not a UX problem, not a storage problem. The question that must be answered before anything else can proceed is simple: how does a second device prove it belongs to the same person, in a way that every group member can independently verify, without any central authority vouching for the claim? Marmot PR #44 introduces MIP-06 to answer exactly this question for White Noise.