I'm planning on a Stripe-style approach where each user (perhaps even each access token) can choose which version of the database schema they want to query.

I don't have any worries about managing long-term schema migrations though because the per-user databases get blown away and reconstructed every time the calendars are refreshed.

At the moment there's just an `events` table but I might handle migrations by having: `events_v1`, `events_v2`, etc. and just have `events` be an SQL view onto the version you chose.

Managing as little persistent state myself was a specific goal so this project is perfect because apart from some authentication info and a list of iCal URLs, the source of truth for your calendar is always with Google/Microsoft/etc.