Conditional <SelectionContextProvider> wrapper. Mounts a provider only
when no parent provider is in scope — otherwise renders children unwrapped
so callers (e.g. <WeaselProvider>) defer to the host's existing scope.
Mirrors ActionsProviderIfRoot / DepRegistryProviderIfRoot.
Conditional
<SelectionContextProvider>wrapper. Mounts a provider only when no parent provider is in scope — otherwise renders children unwrapped so callers (e.g.<WeaselProvider>) defer to the host's existing scope. MirrorsActionsProviderIfRoot/DepRegistryProviderIfRoot.