QueryOptions<TQueryData> class base Options

Everything the cache entry for a query needs: its queryKey, the queryFn that fetches it, and how long and how hard to keep it — staleTime, gcTime, retry, retryDelay, networkMode, enabled, initialData, structuralSharing and meta.

This is what the imperative QueryClient.query takes, which fetches once and completes with the data. An observer — a widget watching the query — takes QueryObserverOptions or QuerySelectOptions instead, which add what only a watcher cares about: when to refetch (refetchOnMount, refetchOnWindowFocus, refetchOnReconnect, refetchInterval), placeholderData, and select. Both extend this class, so one options helper can serve both paths.

null means unset on every option field. An unset field takes the default registered for the key with QueryClient.setQueryDefaults, then the client's DefaultOptions, then the library default each field's documentation names. An option with a real "off" value says so with a value — RefetchInterval.off, RetryPolicy.never, Enabled.no — never with null.

QueryObserverOptions<List<Todo>> todosQuery() => QueryObserverOptions(
      queryKey: QueryKey(['todos']),
      queryFn: (context) => api.fetchTodos(),
      staleTime: const StaleTime.duration(Duration(minutes: 1)),
    );

final todos = await client.query(todosQuery());

No value equality, on purpose: options built inline in a build are re-applied on every build, and the observer works out what actually changed by comparing the resolved values — so two inline closures for queryFn do not count as a change, and neither does a fresh Enabled.when(…).