The root QueryClient is created once and survives every client-side
navigation, so logout then login on the same browser left the previous
account's non-user-scoped health-data queries in memory and the next
account read them before any refetch landed. Wipe the entire in-memory
cache on logout, on session expiry, and at the start of a fresh login,
alongside the existing IndexedDB and service-worker cache wipe, so no
session ever inherits another account's data.