fix(external-system-gateway): resolve ExternalSystemGateway-015..017 — treat MaxRetries=0 as unset, scope HTTP connection cap to gateway clients, no bare trailing '?'

tests/ScadaLink.ExternalSystemGateway.Tests/ServiceWiringTests.cs

@@ -40,6 +40,52 @@ public class ServiceWiringTests
         Assert.Equal(4, sockets.MaxConnectionsPerServer);
     }
 
+    [Fact]
+    public void MaxConcurrentConnectionsPerSystem_IsNotAppliedToNonGatewayHttpClients()
+    {
+        // ExternalSystemGateway-016: the gateway's connection cap must be scoped to
+        // its own per-system clients ("ExternalSystem_{name}"). It must NOT leak onto
+        // unrelated HttpClient consumers in the same host process (e.g. the
+        // Notification Service's OAuth2 token client) — that would silently throttle
+        // and override the primary-handler configuration of another component.
+        var config = new ConfigurationBuilder()
+            .AddInMemoryCollection(new Dictionary<string, string?>
+            {
+                ["ScadaLink:ExternalSystemGateway:MaxConcurrentConnectionsPerSystem"] = "4",
+            })
+            .Build();
+
+        var services = new ServiceCollection();
+        services.AddLogging();
+        services.AddSingleton<IConfiguration>(config);
+        services.AddSingleton(Substitute.For<IExternalSystemRepository>());
+        services.AddExternalSystemGateway();
+
+        // A client owned by a different component, registered the way the
+        // Notification Service registers its OAuth2 token client — a plain
+        // AddHttpClient with no custom primary handler. Its primary handler must
+        // remain the framework default (uncapped), not the gateway's SocketsHttpHandler.
+        services.AddHttpClient("NotificationService_OAuth2");
+
+        using var provider = services.BuildServiceProvider();
+        var handlerFactory = provider.GetRequiredService<IHttpMessageHandlerFactory>();
+
+        // The gateway's own client must still get the gateway cap.
+        var gatewayPrimary = FindPrimaryHandler(handlerFactory.CreateHandler("ExternalSystem_AnySystem"));
+        Assert.Equal(4, Assert.IsType<SocketsHttpHandler>(gatewayPrimary).MaxConnectionsPerServer);
+
+        // The unrelated component's client must NOT inherit the gateway's connection
+        // cap. With ConfigureHttpClientDefaults the primary handler is a
+        // SocketsHttpHandler capped at the gateway's value (the leak); with a scoped
+        // registration it is the framework default whose MaxConnectionsPerServer is
+        // int.MaxValue.
+        var otherPrimary = FindPrimaryHandler(handlerFactory.CreateHandler("NotificationService_OAuth2"));
+        if (otherPrimary is SocketsHttpHandler otherSockets)
+        {
+            Assert.NotEqual(4, otherSockets.MaxConnectionsPerServer);
+        }
+    }
+
     private static HttpMessageHandler FindPrimaryHandler(HttpMessageHandler handler)
     {
         var current = handler;