High performance servers and frameworks will always have to think about the underlying sockets

Not TCP specifically, but ASP.NET Core binds your controller/action methods' CancellationToken parameter (if present) to HttpContext.RequestAborted - so assuming one uses it correctly (e.g. tying it to things like SQL TRANSACTION/ROLLBACK) then that helps prevent inadvertent changes if the user clicked their browser's Stop button after a POST, or gracefully handle long file upload failures, and so on.