Blazor 404 code re-execution is compatible with OnNavigateAsync

[ilonatommy]

Do not prevent rendering for router that has OnNavigateAsync when navigation already started

Description

In #24225 we blocked rendering when Router has a pending OnNavigateAsync task to prevent exceptions during lazy loading (#24211). The reason was that rendering was throwing when triggered before with lazy loading finished: #24211. However, this blocking prevented the prerendering quiescence detection mechanism from working correctly, as the OnNavigateAsync task was not being tracked.

This PR fixes the issue by informing the renderer that the OnNavigateAsync task is part of the quiescence state, allowing prerendering to wait for it to complete before finalizing the response.

Changes

• Added internal RenderHandle.AddPendingTask to allow components to register tasks that should be tracked for quiescence
• Modified Router.RunOnNavigateAsync to register the OnNavigateAsync task with the render handle using _renderHandle.AddPendingTask
• Improved variable naming in the task unwrapping code for clarity (whenAnyTask and firstCompletedTask)
• Added test for the issue: BrowserNavigationToNotExistingPath_ReExecutesTo404.
• Added comprehensive test for Don't render route component if OnNavigateAsync task in-progress #24225 that validates rendering waits for OnNavigateAsync completion during lazy loading: BrowserNavigationToLazyLoadedRoute_WaitsForOnNavigateAsyncGuard.

How it works

During prerendering, the renderer tracks pending tasks to determine when quiescence has been reached. Then, it flushes the http response and the rendering is finished. By registering the OnNavigateAsync task with the renderer, we ensure that the end of rendering won't happen before OnNavigateAsync is finished.

Fixes #63933

[Copilot]

Pull Request Overview

This PR fixes an issue where Blazor 404 re-execution was not working properly when the Router component had an OnNavigateAsync handler. The fix allows rendering to proceed during 404 re-execution scenarios while still preventing it during client-side navigation when lazy loading is in progress.

Key changes:

• Modified the Router component to differentiate between server-side rendering (SSR) scenarios and client-side navigation
• Updated the navigation blocking logic to check if route data is available from SSR before blocking rendering
• Added comprehensive test coverage for the 404 re-execution scenario with OnNavigateAsync

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/Components/Components/src/Routing/Router.cs	Updated navigation logic to allow rendering during SSR/re-execution while maintaining blocking for client navigation
src/Components/test/testassets/Components.TestServer/RazorComponents/App.razor	Added test infrastructure with configurable OnNavigateAsync handler and query parameter support
src/Components/test/E2ETest/ServerRenderingTests/NoInteractivityTest.cs	Added end-to-end test to verify 404 re-execution works with OnNavigateAsync

[ilonatommy]

Failures of UserStoreTest are not connected, they happen across different PRs and should be quarantined.

[oroztocil]

Looks good 👍

[ilonatommy]

@javiercn's review: use the information if we are interactive or not instead of putting a flag into route data.

[javiercn]

This is adding public API.

We can achieve the same effect in a slightly different way without having to add an additional overload nor additional API to RenderHandle.

The issue is that the router doesn't properly notify that it is still doing work, so we reach quiescence without the router being done (and hence we miss on later updates).

Quiescence is tracked whenever we call SetParametersAsync. Instead of doing things this way, we can keep whatever task we need to pass in a field, and on the call to SetParametersAsync we do something like

if (!_renderHandle.RendererInfo.IsInteractive && _taskWeAddedCallingAddPendingTask != null) 
{
  await _taskWeAddedCallingAddPendingTask;
}

That will have the effect of having that task included in the quiescence computation (as SetParametersAsync won't complete until that task completes).