Handle ObjectDisposedException when closing disposed WebSocket

[Copilot]

WebSocketStream.OnShutdownAsync() calls CloseOutputAsync on an already-disposed ClientWebSocket, which throws ObjectDisposedException. The existing catch filter wraps it in a RelayException and rethrows — surfacing as an unhandled exception to callers.

A disposed WebSocket is already effectively closed, so this should be a no-op.

Changes

• WebSocketStream.cs: Added catch (ObjectDisposedException) before the general catch in both OnShutdownAsync (primary fix) and OnCloseAsync (defense-in-depth). Logs as warning via HandledExceptionAsWarning, consistent with existing error handling patterns.
• AssemblyInfo.cs: Added InternalsVisibleTo for the test assembly.
• WebSocketStreamTests.cs: Tests that ShutdownAsync and CloseAsync do not throw on a disposed ClientWebSocket.

// Before: ObjectDisposedException gets wrapped in RelayException and rethrown
catch (Exception exception) when (!WebSocketExceptionHelper.IsRelayContract(exception))

// After: ObjectDisposedException caught first and handled gracefully
catch (ObjectDisposedException exception)
{
    RelayEventSource.Log.HandledExceptionAsWarning(this, exception);
}
catch (Exception exception) when (!WebSocketExceptionHelper.IsRelayContract(exception))

Original prompt

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This section details on the original issue you should resolve

<issue_title>C# Client may try to close a disposed WebSocket</issue_title>
<issue_description>## Actual Behavior

1. Lets me close a disposed socked which causes an exception

The service threw an unhandled exception, System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'System.Net.WebSockets.ClientWebSocket'.
   at System.Net.WebSockets.ClientWebSocket.ThrowIfNotConnected()
   at System.Net.WebSockets.ClientWebSocket.CloseOutputAsync(WebSocketCloseStatus closeStatus, String statusDescription, CancellationToken cancellationToken)
   at Microsoft.Azure.Relay.WebSocketStream.<OnShutdownAsync>d__32.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.Azure.Relay.HybridConnectionStream.<ShutdownAsync>d__10.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()

2. The problem is very similar to a singalIR issues C# Client may try to close a disposed WebSocket aspnet/SignalR#1004

azure-relay-dotnet/src/Microsoft.Azure.Relay/WebSocketStream.cs

Line 80 in 5e41166

await this.webSocket.CloseAsync(WebSocketCloseStatus.NormalClosure, "CloseAsync", linkedCancelSource.Token).ConfigureAwait(false);

azure-relay-dotnet/src/Microsoft.Azure.Relay/WebSocketStream.cs

Line 153 in 5e41166

await this.webSocket.CloseOutputAsync(WebSocketCloseStatus.NormalClosure, "Shutdown", linkedCancelSource.Token).ConfigureAwait(false);

The real issue is that the websockets client throws :(
https://github.com/dotnet/runtime/blob/d6bf13a39c8ccb8fa7815a2f7e4387120a837138/src/libraries/System.Net.WebSockets.Client/src/System/Net/WebSockets/ClientWebSocket.cs#L226

Expected Behavior

1. Do not throw on closing a disposed socket
2. or throw? Doesn't seem correct since even singalIR addressed the issue.

Versions

• OS platform and version:
• .NET Version:
• NuGet package version or commit ID:</issue_description>

<agent_instructions>Create a new branch with a test that reproduces this issue and this exception if possible. If there is an exception, create an appropriate fix. Finally, create a PR.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes C# Client may try to close a disposed WebSocket #137

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