StatefulShellRoute provides a way to implement tabbed navigation with preserved state for each branch (shell). However, I can't find a way to attach NavigatorObserver instances (like RouteObserver) specifically to the nested Navigator widget(s) it manages internally for its branches.

This is a problem when trying to use standard Flutter patterns like the RouteAware mixin on pages within a StatefulShellRoute branch. RouteAware relies on ModalRoute.of(context) to find its associated route and navigator, and then subscribes to a RouteObserver associated with that navigator.

If a RouteObserver is only added to the top-level GoRouter constructor's observers list, it only observes the root navigator. Navigation events happening within the StatefulShellRoute's nested navigator (e.g., pushing a detail page onto a branch's initial page) are not seen by the global observer. Consequently, RouteAware methods (didPush, didPop, didPopNext, didPushNext) do not get called for pages managed by the StatefulShellRoute's navigator.

Example Scenario:

1. App uses StatefulShellRoute for bottom navigation (e.g., Tabs A, B, C).
2. Tab A's initial route is /a.
3. From /a, the user navigates to /a/detail. The DetailPage uses RouteAware.
4. A global RouteObserver is added via GoRouter(observers: [myGlobalObserver]).
5. The DetailPage subscribes using myGlobalObserver.subscribe(this, ModalRoute.of(context)!).
6. Problem: The ModalRoute.of(context) correctly finds the route within the shell's navigator, but myGlobalObserver is not attached to that specific navigator, so the RouteAware callbacks on DetailPage never fire when navigating to/from it within Tab A.

Proposed Solution:

Add an observers parameter to the StatefulShellRoute definition (and consequently to the TypedStatefulShellRoute annotation helper). This parameter would accept a List.

// Example using annotations (Conceptual)
@TypedStatefulShellRoute<AuthenticatedShellRouteData>(
  // <<< Proposed Parameter >>>
  observers: [shellRouteObserver], // Allow passing observers here
  branches: <TypedStatefulShellBranch<StatefulShellBranchData>>[
    // ... branches ...
  ]
)
class AuthenticatedShellRouteData extends StatefulShellRouteData {
  // ...
}

// Or directly on StatefulShellRoute (Conceptual)
StatefulShellRoute(
  builder: ...,
  branches: ...,
  // <<< Proposed Parameter >>>
  observers: [shellRouteObserver],
  navigatorContainerBuilder: ...,
)

These observers would then be attached to the nested Navigator widget(s) created and managed by the StatefulShellRoute for its branches.