Yeah, in practice, each client maintains a persistent data structure, where each "mutation" is the application of a single operation. If a new operation comes i

Yeah, in practice, each client maintains a persistent data structure, where each "mutation" is the application of a single operation. If a new operation comes in that occurs before other operations that have already been applied to the persistent data structure, then the client rewinds the structure to its state just before the new out-of-order operation, applies that operation, and then applies the rest of the operations that it already has. (I think of this as very similar to a `git rebase`.) But yeah, this might not work at all for sequences. And of course, there are other issues with respect to the memory requirements of the persistent data structure in the client. Some sort of compaction is probably necessary.