Which Image Source Does GitHub Codespaces Prioritize When a Floating Base Image Tag Changes?

Repeatable Development Environments with Codespaces

When a repository commits a devcontainer.json that uses a floating base-image tag (e.g., ubuntu:latest), the same file can resolve to different image layers over time. A Codespace prebuild captures the resolved image at the moment the prebuild is created, potentially storing an older digest that no longer matches the floating tag's current value.

Unresolved Decision Point

If a user opens a new Codespace from the same commit after the floating tag has moved to a newer digest, does Codespaces reuse the existing prebuilt image (which reflects the old digest) or does it resolve the current tag and build a fresh container, thereby overriding the prebuild?

Specific Question

Which image source—the prebuilt image captured at the time of the prebuild or the current image reference resolved from the floating tag—should GitHub Codespaces prioritize when the tag has changed but the prebuild is still valid for the commit?