Fix classification of disposal-during-reconnect as cancelled, not failed

[jpablo2002]

Problem

We currently see multiple host_reconnect_failed errors with ObjectDisposedException: RelayTunnelConnector is disposed. These are logged at error severity and pollute dashboards, but they are not actual reconnect failures — the host application called DisposeAsync() while the SDK's reconnect retry loop was in flight, cancelling it.

The causal chain is:

1. Relay pod restarts → WebSocket drops → SSH Closed event fires
2. SDK starts ReconnectAsync(DisposeToken) as a background task
3. MaybeStartReconnecting sets ConnectionStatus = Connecting, which fires ConnectionStatusChanged synchronously to the host app
4. Host app (e.g. Codespaces Agent) reacts to the status change by cancelling a token or exiting an await using scope → DisposeAsync() is called
5. DisposeAsync() cancels disposeCts → DisposeToken cancelled → reconnect retry loop aborted
6. OperationCanceledException is wrapped as ObjectDisposedException by TryAdjustCancellation
7. ReconnectAsync catches it and reports host_reconnect_failed at error severity — indistinguishable from a genuine failure

Fix

In ReconnectAsync, check whether the exception was caused by disposal-cancellation before choosing the event name and severity:

• DisposeToken.IsCancellationRequested AND ex is ObjectDisposedException or OperationCanceledException → report host_reconnect_cancelled at warning severity
• Otherwise → report host_reconnect_failed at error severity (unchanged)

Both conditions must be true to classify as cancelled. If DisposeAsync() was called but the reconnect had already failed with a real error (e.g. WebSocketException, UnauthorizedAccessException), the exception type won't match and it's correctly reported as a failure.

Files Changed

• cs/src/Connections/TunnelRelayConnection.cs — ReconnectAsync catch block now distinguishes disposal-cancelled from genuine failure when reporting telemetry events
• cs/test/TunnelsSDK.Test/Mocks/MockTunnelManagementClient.cs — ReportEvent now captures events in a ReportedEvents list for test assertions
• cs/test/TunnelsSDK.Test/TunnelHostAndClientTests.cs — two new tests:
  • DisposeDuringReconnectReportsCancelledEvent — verifies disposal during reconnect reports _reconnect_cancelled (warning)
  • ReconnectFailureReportsFailedEvent — verifies a genuine reconnect failure reports _reconnect_failed (error)

[jpablo2002]

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