Shouldn't graphcache 9 detect and delete old cached data?

[toerndev]

After upgrading to @urql/exchange-graphcache@9, it crashes on load:

Uncaught (in promise) SyntaxError: Unexpected token 'O', "O" is not valid JSON
    at JSON.parse (<anonymous>)
    at data.ts:720:49
    at data.ts:727:19

Deleting the IndexedDB database fixes the issue.

How can we resolve this at runtime? The code path is

// React root rendered
// ...
// this is needed to call urql's `createClient`:
const myCacheExchange = cacheExchange({
  // ...
  storage: makeDefaultStorage({ idbName, ..., onCacheHydrated: () => ... })
})

There is no hook for validating IDB data here, and the async nature of IDB makes it trickier to scan for a pattern before creating the cache. The React tree below the API provider would need to be deferred while this scan is done.

It should probably be the responsibility of graphcache to detect legacy data and clear it, since it's already making itself available to the client asynchronously without blocking it. It's also hard for consumers to know how to detect old cache data.