[Copilot]

.NET 11 RC 1 marks IStartupValidator obsolete with warning SYSLIB0066, while retaining the interface and its runtime behavior. New custom validators should use the independent asynchronous contract.

• Compatibility guidance: Add the .NET 11 Extensions breaking-change article with migration and registration guidance, including that ValidateOnStart() users who don’t implement startup-validator interfaces normally need no change.
• Diagnostic coverage: Add the SYSLIB0066 article with migration and warning-suppression guidance; cross-link it with the compatibility article.
• Indexes: Update the .NET 11 compatibility overview and TOC, the obsoletions overview, and the diagnostics TOC.

public sealed class StartupValidator : IAsyncStartupValidator
{
    public Task ValidateAsync(CancellationToken cancellationToken = default) =>
        ValidateConfigurationAsync(cancellationToken);
}

services.AddSingleton<IAsyncStartupValidator, StartupValidator>();

• Fixes [Breaking change]: IStartupValidator is obsolete #56348

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Internal previews

File	Preview link
docs/core/compatibility/core-libraries/11/obsolete-apis.md	Learn preview
docs/fundamentals/syslib-diagnostics/obsoletions-overview.md	Learn preview
docs/fundamentals/syslib-diagnostics/syslib0066.md	Learn preview
docs/navigate/tools-diagnostics/toc.yml	Learn preview

Build report

[Copilot]

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[BillWagner]

This LGTM.

[BillWagner]

@copilot please address these comments.

[Copilot]

@copilot please address these comments.

Addressed the article feedback: restored the SYSLIB0066 index row, affected API section, and See also link while keeping the misplaced migration paragraph removed. Markdown lint passes; the change is local and uncommitted, so no commit hash is available.