feat(lmxproxy): phase 1 — v2 protocol types and domain model

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lmxproxy/src-reference/ZB.MOM.WW.LmxProxy.Host/Domain/ConnectionStateChangedEventArgs.cs

@@ -0,0 +1,45 @@
+using System;
+
+namespace ZB.MOM.WW.LmxProxy.Host.Domain
+{
+    /// <summary>
+    ///     Event arguments for SCADA client connection state changes.
+    /// </summary>
+    public class ConnectionStateChangedEventArgs : EventArgs
+    {
+        /// <summary>
+        ///     Initializes a new instance of the <see cref="ConnectionStateChangedEventArgs" /> class.
+        /// </summary>
+        /// <param name="previousState">The previous connection state.</param>
+        /// <param name="currentState">The current connection state.</param>
+        /// <param name="message">Optional message providing additional information about the state change.</param>
+        public ConnectionStateChangedEventArgs(ConnectionState previousState, ConnectionState currentState,
+            string? message = null)
+        {
+            PreviousState = previousState;
+            CurrentState = currentState;
+            Timestamp = DateTime.UtcNow;
+            Message = message;
+        }
+
+        /// <summary>
+        ///     Gets the previous connection state.
+        /// </summary>
+        public ConnectionState PreviousState { get; }
+
+        /// <summary>
+        ///     Gets the current connection state.
+        /// </summary>
+        public ConnectionState CurrentState { get; }
+
+        /// <summary>
+        ///     Gets the timestamp when the state change occurred.
+        /// </summary>
+        public DateTime Timestamp { get; }
+
+        /// <summary>
+        ///     Gets additional information about the state change, such as error messages.
+        /// </summary>
+        public string? Message { get; }
+    }
+}