How to automatically update Swarm services when the Docker daemon restarts
You don't need a restart policy with swarm mode. Swarm mode will constantly try to reconcile any differences between the current and target state. I've seen cases where the restart policy enforced by the docker engine, and the implicit reconciliation in swarm mode have conflicted and resulted in issues. The restart policy would also restart the stopped container which would implicitly break the goal to use a new image since the image can not change for the life of a container. Swarm mode, conversely, will recreate any stopped containers with a new container.

To have swarm use the current value of a tag, rather than resolving that tag to an image digest on the initial deploy, you need docker stack deploy --resolve-image .... Note that I haven't tested if this will pull new images, I've only needed to use the feature to use locally built images that shouldn't be pulled from a registry. If Swarm mode doesn't pull new images, you'll also want an extra process to pull your image periodically.