A *lot* of change, probably the most significant of which is that most refactorings are now two-stage: first they deliver a set of changes to the client, then the client ask for them to be performed. This gives the client a lot more control over the process (i.e. they can refresh buffers as necessary, etc.)
Other changes are that we no longer use actors or attempt any real state management. This seems more responsive, and is certainly a more straightforward design.