fix(communication): resolve Communication-012..015 — endpoint-aware gRPC client cache, address-change recreation, correlation-id validation, node-flip tests

tests/ScadaLink.Communication.Tests/Grpc/SiteStreamGrpcClientFactoryTests.cs

@@ -63,4 +63,70 @@ public class SiteStreamGrpcClientFactoryTests
         // After dispose, creating new clients should work (new instances)
         // This tests that Dispose doesn't throw
     }
+
+    [Fact]
+    public void GetOrCreate_EndpointChanged_ReturnsClientBoundToNewEndpoint()
+    {
+        // Communication-012 regression: when the same site is requested with a
+        // *different* endpoint (the NodeA→NodeB failover flip), the factory must
+        // hand back a client bound to the new endpoint, not the stale cached one.
+        using var factory = new TrackingEndpointFactory();
+
+        var nodeA = factory.GetOrCreate("site-a", "http://localhost:5100");
+        var nodeB = factory.GetOrCreate("site-a", "http://localhost:5200");
+
+        Assert.NotSame(nodeA, nodeB);
+        Assert.Equal("http://localhost:5100", nodeA.Endpoint);
+        Assert.Equal("http://localhost:5200", nodeB.Endpoint);
+    }
+
+    [Fact]
+    public void GetOrCreate_EndpointChanged_DisposesPriorClient()
+    {
+        // Communication-013 regression: a later edit to a site's gRPC address must
+        // invalidate (and dispose) the stale cached client, so the corrected
+        // endpoint takes effect without a central restart.
+        using var factory = new TrackingEndpointFactory();
+
+        var first = (TrackingEndpointClient)factory.GetOrCreate("site-a", "http://localhost:5100");
+        var second = (TrackingEndpointClient)factory.GetOrCreate("site-a", "http://localhost:5200");
+
+        Assert.NotSame(first, second);
+        Assert.True(first.Disposed, "stale client for the old endpoint should be disposed");
+        Assert.False(second.Disposed, "fresh client for the new endpoint should still be live");
+    }
+
+    [Fact]
+    public void GetOrCreate_SameEndpoint_DoesNotDisposeOrRecreate()
+    {
+        // Endpoint unchanged → the cached client is reused untouched.
+        using var factory = new TrackingEndpointFactory();
+
+        var first = (TrackingEndpointClient)factory.GetOrCreate("site-a", "http://localhost:5100");
+        var second = (TrackingEndpointClient)factory.GetOrCreate("site-a", "http://localhost:5100");
+
+        Assert.Same(first, second);
+        Assert.False(first.Disposed);
+    }
+
+    /// <summary>Test client that records its endpoint and disposal (no real channel).</summary>
+    private sealed class TrackingEndpointClient : SiteStreamGrpcClient
+    {
+        public TrackingEndpointClient(string endpoint) : base(endpoint) { }
+        public bool Disposed { get; private set; }
+        public override void Dispose() => Disposed = true;
+        public override ValueTask DisposeAsync()
+        {
+            Disposed = true;
+            return ValueTask.CompletedTask;
+        }
+    }
+
+    /// <summary>Factory that hands out endpoint-tracking clients.</summary>
+    private sealed class TrackingEndpointFactory : SiteStreamGrpcClientFactory
+    {
+        public TrackingEndpointFactory() : base(NullLoggerFactory.Instance) { }
+        protected override SiteStreamGrpcClient CreateClient(string grpcEndpoint)
+            => new TrackingEndpointClient(grpcEndpoint);
+    }
 }