Preview only runs validation and writes nothing to the registry. Use this step to check whether the bundle is installable, see errors and warnings, and review values that were auto-analyzed or inferred.

Publish actually registers the bundle in the registry and can't be undone — once published, you can't upload the same name and version again; you can only yank it.

The Publish button only appears once the most recent Preview reports the bundle as installable with zero warnings, and clicking it opens a confirmation dialog that shows the target name and version again.