SQLite only has some limited support for concurrency, and it looks like it's not enough for us, as it caused an error while @moranegg was doing a demo yesterday: https://sentry.softwareheritage.org/share/issue/7b8cc0d9f4134051979b9b8cb166605c/
My guess is, she clicked "Save code now" right when an other transaction was being committed to the DB.