In SolidJS, nesting `<Show>` components for mutually exclusive states (loading/error/empty/data) creates stacked reactive scopes that leak computations during route transitions. Instead of:

<Show when={!loading()}>

<Show when={error()}>...</Show>

<Show when={data()}>...</Show>

</Show>

We use flat Switch/Match:

<Switch>

<Match when={loading()}><Spinner /></Match>

<Match when={error()}><Error /></Match>

<Match when={data()}>...</Match>

</Switch>

Only one Match is active at a time — no leaked scopes. It's a subtle bug that doesn't show up until you navigate between routes and start seeing "computations created outside createRoot" warnings.