Upload fails: "This is not a valid EPUB 3 publication. This library only supports EPUB 3, not EPUB 2. Use Epub.upgrade(path) to convert."

Uploading an EPUB 2 to my self-hosted instance fails. The client reports tus: unexpected response while uploading chunk ... response code: 500 ... This is not a valid EPUB 3 publication. This library only supports EPUB 3, not EPUB 2. Use Epub.upgrade(path) to convert. and the server log shows the same error thrown from J.from inside onUploadFinish. The same file uploads fine on a hosted instance, and I believed I had already pulled the latest image.

Resolution: Current Storyteller versions convert EPUB 2 to EPUB 3 for you on upload, so hitting this error means you are running an older build -- Epub.upgrade(path) is an internal call in the underlying EPUB library that you should never be told to run yourself, and there is no setting to enable. Do not trust the image tag or registry metadata to tell you what is actually running: hover the sidebar in the web app and the running version is printed under the Storyteller logo. In this case the registry image was :latest (2.13.2) while the running container was still 2.11.13. Fix: re-pull and recreate the container, not just restart it -- docker compose pull && docker compose up -d, or in Docker Desktop/Portainer stop and remove the old container and start a fresh one from the newly pulled image -- then re-check the version under the logo. Back up your data volume before upgrading. If you deliberately want to keep EPUB 2 files unconverted, that is what the Epub 2 strategy setting controls.