A development team pushes container images to an Amazon ECR repository as part of their CI pipeline. Each build tags the image with a fixed value like 'prod-latest'. During an incident review, engineers discover that a broken image had overwritten a previously working image that used the same tag, making rollback impossible because the older digest was no longer retrievable by that tag. The team wants to prevent any future build from overwriting an existing tag in the repository. Which action best addresses this requirement?