How does the `--tag` option interact with a container image name which already contains a tag?

https://github.com/apple/swift-container-plugin/pull/128/files#r2078107925

Passing a fully-qualified destination image name including a tag to the `--repository` flag pushes the image to that repository, tag included. For example "--repository myrepo/myimage:mytag". How does this relate to the use of the `--tag` argument?

The source and destination image names are parsed by the same parser. The source image name can have an optional tag [:tag] or digest [@ sha256:123abc...]. The destination image should only accept an optional tag - a digest should be rejected.

Start by reviewing the PR #128 discussion and the code paths handling --repository and --tag, including the shared image-name parser mentioned in the issue. Determine and document the precedence when the destination already contains a tag, and ensure destination digests are rejected; add or update tests for these cases if the relevant test location is found.

Written by the indexing model from the issue text.