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Claude Code logs every MCP server stderr line at [ERROR] and marks working servers as failed. If your tools still run, it is cosmetic. Here is how to confirm it and quiet the noise.

A complete, working guide to health checks in an ASP.NET Core 11 minimal API: AddHealthChecks and MapHealthChecks, custom IHealthCheck classes returning Healthy/Degraded/Unhealthy, the AddDbContextCheck EF Core probe, tag-based liveness and readiness endpoints for Kubernetes, a JSON ResponseWriter, ResultStatusCodes, securing the endpoint with RequireAuthorization and RequireHost, and pushing results with IHealthCheckPublisher.

A complete, working guide to endpoint filters in an ASP.NET Core 11 minimal API: AddEndpointFilter with an inline delegate, IEndpointFilter classes with DI, GetArgument and the Arguments list, short-circuiting with Results.Problem, FIFO/FILO ordering across multiple filters, group-level filters on MapGroup, and AddEndpointFilterFactory for signature-aware filters.

See the exact SQL Entity Framework Core 11 sends to your database, with parameter values, using LogTo, Microsoft.Extensions.Logging, and ToQueryString.

.NET 11 Preview 6 removes the separate Mono path for MAUI on Android, iOS, and Mac Catalyst. CoreCLR is now the only mobile runtime, the UseMonoRuntime escape hatch is closed, and GA is set for November 2026.

Extension indexers landed in .NET 11 Preview 6, letting you add this[...] access to types you do not own. They complete the extension members story that started with methods and properties in C# 14.

This error means the BuildContext you passed is above the Scaffold or ScaffoldMessenger, not below it. Wrap the caller in a Builder, extract it into its own widget, or use a GlobalKey.

This runtime error means a null reached a cast expecting a non-nullable type, almost always from JSON. Make the field nullable, or supply a default before the cast runs.

There is no single Skill type in the Microsoft Agent Framework, but you can package domain expertise as a reusable agent, reuse it in-process with AsAIFunction, and advertise it across frameworks as an A2A AgentSkill. Full walkthrough on Agent Framework 1.0 and .NET 11.

Preview 6 rejects unsafe cross-origin browser requests by default, reading the Sec-Fetch-Site header instead of an antiforgery token. Here is what it blocks and how to opt out.