Ensure requests use system proxy

Program.cs

@@ -160,7 +160,8 @@ class Program
 
         if (resp == null || !resp.Raw.Contains("200"))
         {
-            Log.Error($"[conn:{connectionId}] upstream CONNECT rejected");
+            var status = resp?.Raw?.Split("\r\n", StringSplitOptions.None).FirstOrDefault() ?? "<no response>";
+            Log.Error($"[conn:{connectionId}] upstream CONNECT rejected: {status}");
             await clientStream.WriteAsync(Encoding.ASCII.GetBytes("HTTP/1.1 502 Bad Gateway\r\n\r\n"));
             return;
         }
@@ -272,13 +273,42 @@ class Program
         }
         catch (Exception ex)
         {
-            Log.Error($"[{context}] stream pump failed", ex);
+            if (IsExpectedDisconnect(ex))
+                Log.Info($"[{context}] stream closed: {OneLine(ex.Message)}");
+            else
+                Log.Error($"[{context}] stream pump failed", ex);
         }
         finally
         {
             ArrayPool<byte>.Shared.Return(buffer);
         }
     }
+
+    static bool IsExpectedDisconnect(Exception ex)
+    {
+        if (ex is ObjectDisposedException)
+            return true;
+        if (ex is OperationCanceledException)
+            return true;
+
+        if (ex is IOException io && io.InnerException is SocketException se)
+        {
+            return se.SocketErrorCode == SocketError.ConnectionAborted
+                || se.SocketErrorCode == SocketError.ConnectionReset
+                || se.SocketErrorCode == SocketError.Shutdown
+                || se.SocketErrorCode == SocketError.OperationAborted
+                || se.SocketErrorCode == SocketError.TimedOut;
+        }
+
+        return false;
+    }
+
+    static string OneLine(string message)
+    {
+        if (string.IsNullOrEmpty(message))
+            return string.Empty;
+        return message.Replace("\r", " ").Replace("\n", " ").Trim();
+    }
 }
 
 // ================= WINHTTP =================