Evaluating Local Environment Variables With Prebuilds

I have a private feature which creates and adds a user to the underlying container. The feature passes all of its tests; it definitely correctly creates a user. I've published the feature image to the GitHub container registry.

When I use this feature with a Dev Container, it works fine. For some reason, when I pre-build and push the Dev Container's image to GHCR, the user is no longer present in the pre-built image.

When I look at the build logs, the feature is definitely being installed. For some reason, all of the "work" that feature does is not present in the pre-built image.

Do you have any suggestions for troubleshooting this issue?