Stale SWR hydration entries (per-chat-session/per-room message caches up to
500KB each) were never garbage-collected — readCache returned null for stale
entries but left the bytes on disk, and nothing swept abandoned caches. This
caused localStorage quota exhaustion for users with many projects and chat
sessions.
Three fixes:
- readCache now lazily deletes stale entries (behavior-preserving; every
reader already treats stale as a miss and re-fetches)
- Boot sweep pruneStaleCacheEntries() in DashboardLoader removes any
kb-dashboard-* entry older than 24h before hydration hooks read caches
- Settings > General "Browser Data" panel with a Clear local data button
that wipes all Fusion-owned browser data while preserving the auth token
Also completes the vitest localStorage mock (was missing length/key).
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