When the knot is initialized, the h.init channel is closed signalling the Jetstream watcher to begin, with the owner DID in filter. There's no null filter so starting it without any DIDs will give us events for all DIDs. /init also checks if h.knotInitialized is true, and will 409 Conflict if /init is called again. PUT /user is similar, but will only trigger a call to UpdateDids.