feat(lmxproxy): phase 7 — integration test project and test scenarios

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

lmxproxy/tests/ZB.MOM.WW.LmxProxy.Client.IntegrationTests/WriteTests.cs

@@ -0,0 +1,30 @@
+using ZB.MOM.WW.LmxProxy.Client.Domain;
+
+namespace ZB.MOM.WW.LmxProxy.Client.IntegrationTests;
+
+public class WriteTests : IntegrationTestBase
+{
+    [Fact]
+    public async Task WriteAndReadBack_StringValue()
+    {
+        string testValue = $"IntTest-{DateTime.UtcNow:HHmmss}";
+        await Client!.WriteAsync("TestChildObject.TestString",
+            new TypedValue { StringValue = testValue });
+
+        await Task.Delay(500); // Allow time for write to propagate
+        var vtq = await Client.ReadAsync("TestChildObject.TestString");
+        Assert.Equal(testValue, vtq.Value);
+    }
+
+    [Fact]
+    public async Task WriteWithReadOnlyKey_ThrowsPermissionDenied()
+    {
+        using var readOnlyClient = CreateClient(ReadOnlyApiKey);
+        await readOnlyClient.ConnectAsync();
+
+        var ex = await Assert.ThrowsAsync<Grpc.Core.RpcException>(
+            () => readOnlyClient.WriteAsync("TestChildObject.TestString",
+                new TypedValue { StringValue = "should-fail" }));
+        Assert.Equal(Grpc.Core.StatusCode.PermissionDenied, ex.StatusCode);
+    }
+}