The projection actor is responsible in preparing data for the HTTP API and consequently for the UI.
While this is commit provides only the foundation, in the long run we can:
- Reduce the logic happening in the rocket layer. `ToSseEvent` can likely go away.
- Reduce the complexity for other actors in what needs to be updated when. All they should care about is sending updates to the projection actor. (mostly done)
- Improve test coverage. With a dedicated actor that does the projection, we should be able to write assertions in our integration tests that are closer to the UI.
bonomat