feat(lmxproxy): phase 5 — client core (ILmxProxyClient, connection, read/write/subscribe)

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

lmxproxy/tests/ZB.MOM.WW.LmxProxy.Client.Tests/Fakes/TestableClient.cs

@@ -0,0 +1,50 @@
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
+using ZB.MOM.WW.LmxProxy.Client.Domain;
+
+namespace ZB.MOM.WW.LmxProxy.Client.Tests.Fakes;
+
+/// <summary>
+/// Helper to create an LmxProxyClient wired to a FakeScadaService, bypassing real gRPC.
+/// Uses reflection to set private fields since the client has no test seam for IScadaService injection.
+/// </summary>
+internal static class TestableClient
+{
+    /// <summary>
+    /// Creates an LmxProxyClient with a fake service injected into its internal state,
+    /// simulating a connected client.
+    /// </summary>
+    public static (LmxProxyClient Client, FakeScadaService Fake) CreateConnected(
+        string sessionId = "test-session-123",
+        ILogger<LmxProxyClient>? logger = null)
+    {
+        var fake = new FakeScadaService
+        {
+            ConnectResponseToReturn = new ConnectResponse
+            {
+                Success = true,
+                SessionId = sessionId,
+                Message = "OK"
+            }
+        };
+
+        var client = new LmxProxyClient("localhost", 50051, "test-key", null, logger);
+
+        // Use reflection to inject fake service and simulate connected state
+        var clientType = typeof(LmxProxyClient);
+
+        var clientField = clientType.GetField("_client",
+            System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance)!;
+        clientField.SetValue(client, fake);
+
+        var sessionField = clientType.GetField("_sessionId",
+            System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance)!;
+        sessionField.SetValue(client, sessionId);
+
+        var connectedField = clientType.GetField("_isConnected",
+            System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance)!;
+        connectedField.SetValue(client, true);
+
+        return (client, fake);
+    }
+}