feat: add runtime profiling parity and close config runtime drift

tests/NATS.Server.Tests/ConfigRuntimeParityTests.cs

@@ -0,0 +1,36 @@
+using NATS.Server.Configuration;
+
+namespace NATS.Server.Tests;
+
+public class ConfigRuntimeParityTests
+{
+    [Fact]
+    public async Task Profiling_endpoint_returns_runtime_profile_artifacts_and_config_options_map_to_runtime_behavior()
+    {
+        _ = await Task.FromResult(0);
+
+        var oldOpts = new NatsOptions
+        {
+            Mqtt = new MqttOptions
+            {
+                SessionPersistence = true,
+                SessionTtl = TimeSpan.FromMinutes(5),
+                Qos1PubAck = true,
+            },
+        };
+        var newOpts = new NatsOptions
+        {
+            Mqtt = new MqttOptions
+            {
+                SessionPersistence = false,
+                SessionTtl = TimeSpan.FromMinutes(1),
+                Qos1PubAck = false,
+            },
+        };
+
+        var changes = ConfigReloader.Diff(oldOpts, newOpts);
+        changes.Select(c => c.Name).ShouldContain("Mqtt.SessionPersistence");
+        changes.Select(c => c.Name).ShouldContain("Mqtt.SessionTtl");
+        changes.Select(c => c.Name).ShouldContain("Mqtt.Qos1PubAck");
+    }
+}

tests/NATS.Server.Tests/Monitoring/PprofEndpointTests.cs

@@ -70,6 +70,11 @@ internal sealed class PprofMonitorFixture : IAsyncDisposable
         return _http.GetStringAsync($"http://127.0.0.1:{_monitorPort}{path}");
     }
 
+    public Task<byte[]> GetBytesAsync(string path)
+    {
+        return _http.GetByteArrayAsync($"http://127.0.0.1:{_monitorPort}{path}");
+    }
+
     public async ValueTask DisposeAsync()
     {
         _http.Dispose();

tests/NATS.Server.Tests/Monitoring/PprofRuntimeParityTests.cs

@@ -0,0 +1,18 @@
+using System.Text.Json;
+
+namespace NATS.Server.Tests.Monitoring;
+
+public class PprofRuntimeParityTests
+{
+    [Fact]
+    public async Task Profiling_endpoint_returns_runtime_profile_artifacts_and_config_options_map_to_runtime_behavior()
+    {
+        await using var fx = await PprofMonitorFixture.StartWithProfilingAsync();
+        var payload = await fx.GetBytesAsync("/debug/pprof/profile?seconds=2");
+        var doc = JsonDocument.Parse(payload);
+
+        doc.RootElement.GetProperty("profile").GetString().ShouldBe("cpu");
+        doc.RootElement.GetProperty("seconds").GetInt32().ShouldBe(2);
+        doc.RootElement.GetProperty("thread_count").GetInt32().ShouldBeGreaterThan(0);
+    }
+}