Redirects, Guards, and refresh

A Redirect answers “which typed Target should be used instead?” A Guard answers “may this transition proceed?” Mixing them creates policies that mutate the Controller while it is already resolving a request.

Policies can live at Graph, Module, Mount, or Route Definition level. Redirects run before Guards. Guards run in leave and enter phases, so unsaved-edit protection is independent from destination access control.

final class EditorGuard implements NavigationGuard {
  const EditorGuard(this.editor);
  final EditorState editor;

  @override
  NavigationGuardDecision evaluate(NavigationPolicyContext context) {
    if (context.phase == NavigationGuardPhase.leave && editor.hasDraft) {
      return const NavigationGuardDenied(reason: UnsavedDraft());
    }
    return const NavigationGuardAllowed();
  }
}

Denial reasons are application-owned values, so they can be enums or sealed types. Authentication and feature flags may change while a route is visible; a NavigationPolicyRefresh signal asks the Session to reconcile the current Destination without making every feature issue manual navigation.