feat(mxgateway): export GatewayMetrics via AddZbTelemetry + /metrics (name/units unchanged)

src/ZB.MOM.WW.MxGateway.Server/GatewayApplication.cs

@@ -15,6 +15,7 @@ using ZB.MOM.WW.MxGateway.Server.Security.Authentication;
 using ZB.MOM.WW.MxGateway.Server.Security.Authorization;
 using ZB.MOM.WW.MxGateway.Server.Sessions;
 using ZB.MOM.WW.MxGateway.Server.Workers;
+using ZB.MOM.WW.Telemetry;
 using ZB.MOM.WW.Telemetry.Serilog;
 
 namespace ZB.MOM.WW.MxGateway.Server;
@@ -73,6 +74,11 @@ public static class GatewayApplication
                 failureStatus: null,
                 tags: new[] { ZbHealthTags.Ready });
         builder.Services.AddSingleton<GatewayMetrics>();
+        builder.AddZbTelemetry(o =>
+        {
+            o.ServiceName = "mxgateway";
+            o.Meters = [GatewayMetrics.MeterName]; // "MxGateway.Server" — name unchanged
+        });
         builder.Services.AddSingleton<ILogRedactor, GatewayLogRedactorSeam>();
         builder.Services.AddSingleton<MxAccessGrpcMapper>();
         builder.Services.AddSingleton<MxAccessGrpcRequestValidator>();
@@ -179,6 +185,7 @@ public static class GatewayApplication
         endpoints.MapStaticAssets(ResolveStaticAssetsManifestPath());
 
         endpoints.MapZbHealth();
+        endpoints.MapZbMetrics();
 
         endpoints.MapGrpcService<MxAccessGatewayService>();
         endpoints.MapGrpcService<GalaxyRepositoryGrpcService>();

src/ZB.MOM.WW.MxGateway.Tests/Gateway/GatewayApplicationTests.cs

@@ -1,3 +1,5 @@
+using System.Net;
+using System.Net.Http;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Routing;
@@ -50,6 +52,28 @@ public sealed class GatewayApplicationTests
         Assert.NotNull(metrics);
     }
 
+    /// <summary>Verifies that Build mounts the Prometheus /metrics scrape endpoint.</summary>
+    [Fact]
+    public async Task Build_MapsMetricsEndpoint()
+    {
+        // Bind an ephemeral port (:0) — xUnit runs test collections in parallel, so any
+        // started-host test must avoid a fixed port to prevent a bind collision.
+        await using WebApplication app = GatewayApplication.Build(["--urls=http://127.0.0.1:0"]);
+        await app.StartAsync();
+        try
+        {
+            using var client = new HttpClient { BaseAddress = new Uri(app.Urls.First()) };
+
+            using HttpResponseMessage response = await client.GetAsync("/metrics");
+
+            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+        }
+        finally
+        {
+            await app.StopAsync();
+        }
+    }
+
     /// <summary>Verifies that Build maps dashboard and authentication endpoints when the dashboard is enabled.</summary>
     [Fact]
     public async Task Build_WhenDashboardEnabled_MapsBlazorDashboardAndAuthEndpoints()