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

src/ScadaLink.ExternalSystemGateway/ServiceCollectionExtensions.cs

@@ -1,4 +1,5 @@
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Http;
 using Microsoft.Extensions.Options;
 using ScadaLink.Commons.Interfaces.Services;
 
@@ -6,6 +7,12 @@ namespace ScadaLink.ExternalSystemGateway;
 
 public static class ServiceCollectionExtensions
 {
+    /// <summary>
+    /// Name prefix of the per-system <see cref="System.Net.Http.HttpClient"/> clients
+    /// created by <see cref="ExternalSystemClient"/> (<c>ExternalSystem_{systemName}</c>).
+    /// </summary>
+    internal const string GatewayClientNamePrefix = "ExternalSystem_";
+
     public static IServiceCollection AddExternalSystemGateway(this IServiceCollection services)
     {
         services.AddOptions<ExternalSystemGatewayOptions>()
@@ -13,20 +20,18 @@ public static class ServiceCollectionExtensions
 
         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,
-                };
-            }));
+        // ExternalSystemGateway-013 / -016: wire MaxConcurrentConnectionsPerSystem
+        // into the primary handler of the gateway's per-system named clients
+        // ("ExternalSystem_{name}") only. The names are created dynamically, so a
+        // static AddHttpClient("name") registration is not possible; instead a
+        // post-configure on HttpClientFactoryOptions is applied, filtered by the
+        // client-name prefix. ConfigureHttpClientDefaults is deliberately NOT used —
+        // it is process-global and would replace the primary handler of every
+        // HttpClient in the host (e.g. the Notification Service's OAuth2 token
+        // client), silently capping and overriding unrelated components.
+        services.AddSingleton<IConfigureOptions<HttpClientFactoryOptions>>(sp =>
+            new GatewayHttpClientConfigurator(
+                sp.GetRequiredService<IOptionsMonitor<ExternalSystemGatewayOptions>>()));
 
         services.AddScoped<ExternalSystemClient>();
         services.AddScoped<IExternalSystemClient>(sp => sp.GetRequiredService<ExternalSystemClient>());
@@ -42,4 +47,41 @@ public static class ServiceCollectionExtensions
         // Script Execution Actors run on dedicated blocking I/O dispatcher.
         return services;
     }
+
+    /// <summary>
+    /// ExternalSystemGateway-016: configures the primary HTTP message handler with the
+    /// gateway's <see cref="ExternalSystemGatewayOptions.MaxConcurrentConnectionsPerSystem"/>
+    /// cap, but only for the gateway's own named clients
+    /// (<see cref="GatewayClientNamePrefix"/>). Clients owned by other host components
+    /// are left untouched, so the cap does not leak process-wide.
+    /// </summary>
+    private sealed class GatewayHttpClientConfigurator
+        : IConfigureNamedOptions<HttpClientFactoryOptions>
+    {
+        private readonly IOptionsMonitor<ExternalSystemGatewayOptions> _options;
+
+        public GatewayHttpClientConfigurator(IOptionsMonitor<ExternalSystemGatewayOptions> options)
+        {
+            _options = options;
+        }
+
+        public void Configure(HttpClientFactoryOptions options)
+        {
+            // The default (unnamed) client is not a gateway client — do nothing.
+        }
+
+        public void Configure(string? name, HttpClientFactoryOptions options)
+        {
+            if (name == null || !name.StartsWith(GatewayClientNamePrefix, StringComparison.Ordinal))
+            {
+                return;
+            }
+
+            options.HttpMessageHandlerBuilderActions.Add(builder =>
+                builder.PrimaryHandler = new SocketsHttpHandler
+                {
+                    MaxConnectionsPerServer = _options.CurrentValue.MaxConcurrentConnectionsPerSystem,
+                });
+        }
+    }
 }