Switch from localstorage to IndexedDB for unbounded storage

[prescod]

IndexedDB is unlimited.

Maybe I should also implement warnings for when the chat crosses certain thresholds so you remember to delete your chats and not waste disk space? Let me know if you want that as a fast-follow PR.

But the old way was a hard limit that would crash a demo in the middle.

Fixes #17

[dsfaccini]

hey @prescod , appreciate the contrib! I had claude do a review and we found some points for potential improvement, so I'll push an update and merge later. thanks again!

[dsfaccini]

Claude here: Pushed a follow-up commit with some improvements.

Changes

src/lib/chat-db.ts:

• Replaced window.alert() with toast.error() (sonner) for storage errors
• Removed as typecasts — used typed variable declarations with targeted eslint-disable at IDB/JSON.parse boundaries
• Added db.onclose handler to reset cached dbPromise on connection loss
• Reset dbPromise on open error to avoid reusing a rejected promise
• Deferred localStorage cleanup in migration until all IDB writes succeed
• Typed messages as UIMessage[] end-to-end instead of unknown[]

src/Chat.tsx:

• Changed useLayoutEffect → useEffect for async message loading (layout effect had no benefit with async IDB)
• Removed as typeof messages cast (no longer needed with typed getMessages)
• Removed unused useLayoutEffect import

src/App.tsx:

• Render app shell during migration instead of blank screen — only Chat is gated on migration completion

[github-actions]

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