[release/8.0] [Blazor] Prevent error boundaries from handling exceptions of type NavigationException

[MackinnonBuck]

Prevent error boundaries from handling exceptions of type NavigationException

Backport of #53826

Fixes an issue where error boundaries may handle NavigationException instances and treat them as uncaught errors rather than signals to redirect.

Description

The implementation of NavigationManager.NavigateTo() for static server rendering (SSR) always throws a NavigationException. This exception does not communicate an error but acts as a message to be caught by the framework so a redirect can be initiated.

Blazor also provides an ErrorBoundary component (unrelated to the above) that catches exceptions thrown from within child components, so that errors disable only part of the UI rather than crash the entire page. However, before this PR, the ErrorBoundary component did not account for the fact that exceptions of type NavigationException are not critical errors and need to bubble all the way up to be handled by the framework. As a result, error boundaries would prevent child components from being able to initiate redirects during static server rendering.

This PR updates Blazor's renderer to exclude NavigationException instances from being reported to error boundaries.

Fixes #52777

Customer Impact

We've received multiple reports of customers getting confused by this exception without knowing that its existence is what enables navigation during static server rendering. When an ErrorBoundary catches and displays this exception, many customers are left to believe that the NavigationException is being thrown as a result of navigation not succeeding. Ugly workarounds may exist, like restructuring app logic to ensure that NavigationManager APIs are not used within error boundaries, but something as fundamental as navigation is expected to work without this type of issue.

Regression?

• Yes
• No

This bug has existed since the ability to redirect from within a component was introduced in .NET 8.

Risk

• High
• Medium
• Low

The fix works by adding a special case for NavigationException without changing other functionality, so it's unlikely that a regression will be introduced here.

Verification

• Manual (required)
• Automated

Packaging changes reviewed?

• Yes
• No
• N/A