In some cases launching a session that fails can leave behind its secrets

[olevski]

This should not happen because the notebook service should cleanup when things fail.

What we should also do is recognize this on starting a session. The erorr is 409 if the secrets from a previous session have not been cleaned up. Then we can clean them up and properly start the session.

This happened during the CAS class with GPUs on renkulab.io.

This is the error in sentry:
https://sentry.dev.renku.ch/organizations/sentry/issues/9425/events/0e853e74fc4b499cb74bf3f98abdcd61/