Add prerender support to Brouter (#12410)

src/Bit.CI.Release.slnx

@@ -50,9 +50,9 @@
   <Folder Name="/Brouter/">
     <Project Path="Brouter/Bit.Brouter/Bit.Brouter.csproj" />
   </Folder>
-  <Folder Name="/Brouter/Demo/">
-    <Project Path="Brouter/Demo/Bit.Brouter.Demo.Core/Bit.Brouter.Demo.Core.csproj" />
-    <Project Path="Brouter/Demo/Bit.Brouter.Demo.Web/Bit.Brouter.Demo.Web.csproj" />
+  <Folder Name="/Brouter/InteralTests/Demo/">
+    <Project Path="Brouter/InteralTests/Demo/Bit.Brouter.Demo.Core/Bit.Brouter.Demo.Core.csproj" />
+    <Project Path="Brouter/InteralTests/Demo/Bit.Brouter.Demo.Web/Bit.Brouter.Demo.Web.csproj" />
   </Folder>
   <Folder Name="/Brouter/Tests/">
     <Project Path="Brouter/Tests/Bit.Brouter.Tests/Bit.Brouter.Tests.csproj" />

src/Bit.slnx

@@ -81,12 +81,12 @@
     <File Path="Brouter/README.md" />
     <Project Path="Brouter/Bit.Brouter/Bit.Brouter.csproj" />
   </Folder>
-  <Folder Name="/Brouter/Demo/">
-    <Project Path="Brouter/Demo/Bit.Brouter.Demo.Core/Bit.Brouter.Demo.Core.csproj" />
-    <Project Path="Brouter/Demo/Bit.Brouter.Demo.Maui/Bit.Brouter.Demo.Maui.csproj">
+  <Folder Name="/Brouter/InteralTests/Demo/">
+    <Project Path="Brouter/InteralTests/Demo/Bit.Brouter.Demo.Core/Bit.Brouter.Demo.Core.csproj" />
+    <Project Path="Brouter/InteralTests/Demo/Bit.Brouter.Demo.Maui/Bit.Brouter.Demo.Maui.csproj">
       <Deploy />
     </Project>
-    <Project Path="Brouter/Demo/Bit.Brouter.Demo.Web/Bit.Brouter.Demo.Web.csproj" />
+    <Project Path="Brouter/InteralTests/Demo/Bit.Brouter.Demo.Web/Bit.Brouter.Demo.Web.csproj" />
   </Folder>
   <Folder Name="/Brouter/Tests/">
     <Project Path="Brouter/Tests/Bit.Brouter.Tests/Bit.Brouter.Tests.csproj" />

src/Brouter/Bit.Brouter.slnx

@@ -6,12 +6,19 @@
     <File Path="../global.json" />
     <File Path="README.md" />
   </Folder>
-  <Folder Name="/Demo/">
-    <Project Path="Demo/Bit.Brouter.Demo.Core/Bit.Brouter.Demo.Core.csproj" />
-    <Project Path="Demo/Bit.Brouter.Demo.Maui/Bit.Brouter.Demo.Maui.csproj">
-      <Deploy />
-    </Project>
-    <Project Path="Demo/Bit.Brouter.Demo.Web/Bit.Brouter.Demo.Web.csproj" />
+  <Folder Name="/InteralDemos/">
+    <Project Path="InteralDemos/Core/Bit.Brouter.Demos.Core.csproj" />
+  </Folder>
+  <Folder Name="/InteralDemos/Auto/">
+    <Project Path="InteralDemos/Auto/Bit.Brouter.Demos.Auto.Client/Bit.Brouter.Demos.Auto.Client.csproj" />
+    <Project Path="InteralDemos/Auto/Bit.Brouter.Demos.Auto/Bit.Brouter.Demos.Auto.csproj" />
+  </Folder>
+  <Folder Name="/InteralDemos/Server/">
+    <Project Path="InteralDemos/Server/Bit.Brouter.Demos.Server.csproj" />
+  </Folder>
+  <Folder Name="/InteralDemos/Wasm/">
+    <Project Path="InteralDemos/Wasm/Bit.Brouter.Demos.Wasm.Client/Bit.Brouter.Demos.Wasm.Client.csproj" />
+    <Project Path="InteralDemos/Wasm/Bit.Brouter.Demos.Wasm/Bit.Brouter.Demos.Wasm.csproj" />
   </Folder>
   <Folder Name="/Tests/">
     <Project Path="Tests/Bit.Brouter.Tests/Bit.Brouter.Tests.csproj" />

src/Brouter/Bit.Brouter/Brouter.cs

@@ -118,18 +118,45 @@ protected override void OnInitialized()
         CurrentLocation = ComputeLocation();
     }
 
+    protected override async Task OnInitializedAsync()
+    {
+        await base.OnInitializedAsync();
+
+        // Yield once so ComponentBase performs the initial synchronous render of our
+        // ChildContent. That first render is what causes the declared <BrouterRoute> children to
+        // register themselves with us (each one calls RegisterRoute from its own OnInitialized).
+        // Until they've registered there is nothing to match against, which is why the initial
+        // match cannot run any earlier than this.
+        //
+        // Doing the initial match here - rather than in OnAfterRenderAsync - is what enables
+        // static server prerendering. OnAfterRenderAsync never runs during prerender, so the old
+        // placement left the prerendered HTML empty (no route was ever matched server-side).
+        // OnInitializedAsync, by contrast, runs during prerender and the renderer awaits it - and
+        // the StateHasChanged it triggers - before serializing the HTML, so the matched route is
+        // included in the prerendered output. When the component later becomes interactive its
+        // lifecycle runs again and the match re-runs naturally.
+        await Task.Yield();
+
+        // Initial render: the From is Empty (we just mounted), the To is the URL we're at now.
+        await ProcessNavigationAsync(BrouterLocation.Empty, CurrentLocation);
+    }
+
     protected override async Task OnAfterRenderAsync(bool firstRender)
     {
         await base.OnAfterRenderAsync(firstRender);
 
         if (firstRender is false) return;
 
-        // Enabling navigation interception is best-effort: under prerender, on a disconnected
-        // circuit, or on an interop failure it can throw, but the navigation pipeline itself
-        // (and any subsequent reconnects / interactivity handoff) does not depend on it
-        // succeeding right now. Mirror the defensive style used in BrouterLink and
-        // BrouterService.BackAsync so a transient failure here can't kill the whole first
-        // navigation. Once the circuit/runtime is fully ready, Blazor will retry interception
+        // Enabling navigation interception genuinely requires an interactive runtime, so it stays
+        // in OnAfterRenderAsync, which only runs once interactivity is established. Under prerender
+        // this method doesn't run at all - that's fine: the initial match already happened in
+        // OnInitializedAsync, and interception is enabled here once the component goes interactive.
+        //
+        // Enabling navigation interception is best-effort: on a disconnected circuit or an interop
+        // failure it can throw, but the navigation pipeline itself (and any subsequent reconnects /
+        // interactivity handoff) does not depend on it succeeding right now. Mirror the defensive
+        // style used in BrouterLink and BrouterService.BackAsync so a transient failure here can't
+        // kill navigation. Once the circuit/runtime is fully ready, Blazor will retry interception
         // attachment naturally on the next user click via NavigationManager fallback paths.
         try
         {
@@ -139,9 +166,6 @@ protected override async Task OnAfterRenderAsync(bool firstRender)
         catch (JSException) { /* JS interop failure; non-fatal */ }
         catch (InvalidOperationException) { /* interop unavailable during prerender */ }
         catch (TaskCanceledException) { /* component disposed mid-call */ }
-
-        // Initial render: the From is Empty (we just mounted), the To is the URL we're at now.
-        await ProcessNavigationAsync(BrouterLocation.Empty, CurrentLocation);
     }
 
     protected override void BuildRenderTree(RenderTreeBuilder builder)
@@ -551,6 +575,16 @@ private async ValueTask ProcessNavigationAsync(BrouterLocation from, BrouterLoca
                 {
                     return;
                 }
+                catch (NavigationException)
+                {
+                    // During static server rendering / prerender, NavigationManager.NavigateTo
+                    // throws NavigationException as the framework's redirect signal (a loader may
+                    // redirect, e.g. an auth gate). It must unwind out of OnInitializedAsync so the
+                    // endpoint can issue the HTTP redirect; swallowing it into OnError would drop
+                    // the redirect entirely. Interactive NavigateTo never throws, so this is inert
+                    // outside SSR.
+                    throw;
+                }
                 catch (Exception ex)
                 {
                     await service.InvokeOnError(ctx, ex);
@@ -583,6 +617,13 @@ private async ValueTask ProcessNavigationAsync(BrouterLocation from, BrouterLoca
         {
             // navigation was superseded; nothing to do
         }
+        catch (NavigationException)
+        {
+            // SSR/prerender redirect signal (see the loader catch above). Let it propagate out of
+            // OnInitializedAsync so the framework can turn it into an HTTP redirect. A guard or
+            // OnNavigating handler that redirects via NavigationManager during prerender lands here.
+            throw;
+        }
         catch (Exception ex)
         {
             await service.InvokeOnError(ctx, ex);