fix(external-system-gateway): resolve ExternalSystemGateway-012,013,014 — failure logging, connection-limit wiring, test coverage; ExternalSystemGateway-011 flagged

src/ScadaLink.ExternalSystemGateway/ServiceCollectionExtensions.cs

@@ -1,4 +1,5 @@
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
 using ScadaLink.Commons.Interfaces.Services;
 
 namespace ScadaLink.ExternalSystemGateway;
@@ -11,6 +12,22 @@ public static class ServiceCollectionExtensions
             .BindConfiguration("ScadaLink:ExternalSystemGateway");
 
         services.AddHttpClient();
+
+        // ExternalSystemGateway-013: wire MaxConcurrentConnectionsPerSystem into the
+        // primary handler of every per-system named client ("ExternalSystem_{name}"),
+        // so the option an operator configures actually bounds concurrent connections
+        // instead of being silently ignored. ConfigureHttpClientDefaults applies to
+        // the dynamically-named clients created by ExternalSystemClient.
+        services.ConfigureHttpClientDefaults(builder =>
+            builder.ConfigurePrimaryHttpMessageHandler(sp =>
+            {
+                var options = sp.GetRequiredService<IOptions<ExternalSystemGatewayOptions>>().Value;
+                return new SocketsHttpHandler
+                {
+                    MaxConnectionsPerServer = options.MaxConcurrentConnectionsPerSystem,
+                };
+            }));
+
         services.AddScoped<ExternalSystemClient>();
         services.AddScoped<IExternalSystemClient>(sp => sp.GetRequiredService<ExternalSystemClient>());
         services.AddScoped<DatabaseGateway>();