refactor: rename remaining tests to NATS.Server.Core.Tests

- Rename tests/NATS.Server.Tests -> tests/NATS.Server.Core.Tests
- Update solution file, InternalsVisibleTo, and csproj references
- Remove JETSTREAM_INTEGRATION_MATRIX and NATS.NKeys from csproj (moved to JetStream.Tests and Auth.Tests)
- Update all namespaces from NATS.Server.Tests.* to NATS.Server.Core.Tests.*
- Replace private GetFreePort/ReadUntilAsync helpers with TestUtilities calls
- Fix stale namespace in Transport.Tests/NetworkingGoParityTests.cs

tests/NATS.Server.Core.Tests/ClientTraceTests.cs

@@ -0,0 +1,136 @@
+using NATS.Server;
+using Shouldly;
+
+namespace NATS.Server.Core.Tests;
+
+/// <summary>
+/// Tests for per-client trace delivery and echo control.
+/// Go reference: server/client.go — c.trace, c.echo fields and TraceMsgDelivery / deliverMsg logic.
+/// </summary>
+public class ClientTraceTests
+{
+    // 1. TraceEnabled defaults to false
+    [Fact]
+    public void TraceEnabled_defaults_to_false()
+    {
+        var info = new ClientTraceInfo();
+        info.TraceEnabled.ShouldBeFalse();
+    }
+
+    // 2. EchoEnabled defaults to true
+    [Fact]
+    public void EchoEnabled_defaults_to_true()
+    {
+        var info = new ClientTraceInfo();
+        info.EchoEnabled.ShouldBeTrue();
+    }
+
+    // 3. TraceMsgDelivery records when enabled
+    [Fact]
+    public void TraceMsgDelivery_records_when_enabled()
+    {
+        var info = new ClientTraceInfo();
+        info.TraceEnabled = true;
+
+        info.TraceMsgDelivery("foo.bar", "client-1", 42);
+
+        info.TraceLogCount.ShouldBe(1);
+    }
+
+    // 4. TraceMsgDelivery skips when disabled
+    [Fact]
+    public void TraceMsgDelivery_skips_when_disabled()
+    {
+        var info = new ClientTraceInfo();
+        // TraceEnabled is false by default
+
+        info.TraceMsgDelivery("foo.bar", "client-1", 42);
+
+        info.TraceLogCount.ShouldBe(0);
+    }
+
+    // 5. TraceMsgDelivery captures subject, destination and payload size correctly
+    [Fact]
+    public void TraceMsgDelivery_captures_subject_destination_size()
+    {
+        var info = new ClientTraceInfo();
+        info.TraceEnabled = true;
+        var before = DateTime.UtcNow;
+
+        info.TraceMsgDelivery("orders.new", "client-42", 128);
+
+        var records = info.DrainTraceLog();
+        records.Count.ShouldBe(1);
+        var rec = records[0];
+        rec.Subject.ShouldBe("orders.new");
+        rec.Destination.ShouldBe("client-42");
+        rec.PayloadSize.ShouldBe(128);
+        rec.TimestampUtc.ShouldBeGreaterThanOrEqualTo(before);
+        rec.TimestampUtc.ShouldBeLessThanOrEqualTo(DateTime.UtcNow);
+    }
+
+    // 6. ShouldEcho returns true when echo is enabled (same client)
+    [Fact]
+    public void ShouldEcho_true_when_echo_enabled()
+    {
+        var info = new ClientTraceInfo();
+        info.EchoEnabled = true;
+
+        info.ShouldEcho("client-1", "client-1").ShouldBeTrue();
+    }
+
+    // 7. ShouldEcho returns false when echo is disabled and same client
+    [Fact]
+    public void ShouldEcho_false_when_echo_disabled_same_client()
+    {
+        var info = new ClientTraceInfo();
+        info.EchoEnabled = false;
+
+        info.ShouldEcho("client-1", "client-1").ShouldBeFalse();
+    }
+
+    // 8. ShouldEcho returns true when echo is disabled but different client
+    [Fact]
+    public void ShouldEcho_true_when_echo_disabled_different_client()
+    {
+        var info = new ClientTraceInfo();
+        info.EchoEnabled = false;
+
+        info.ShouldEcho("client-1", "client-2").ShouldBeTrue();
+    }
+
+    // 9. DrainTraceLog returns records and clears the log
+    [Fact]
+    public void DrainTraceLog_returns_and_clears()
+    {
+        var info = new ClientTraceInfo();
+        info.TraceEnabled = true;
+        info.TraceMsgDelivery("a", "dest-a", 10);
+        info.TraceMsgDelivery("b", "dest-b", 20);
+
+        var drained = info.DrainTraceLog();
+
+        drained.Count.ShouldBe(2);
+        info.TraceLogCount.ShouldBe(0);
+    }
+
+    // 10. TraceLogCount reflects current entries before and after drain
+    [Fact]
+    public void TraceLogCount_reflects_current_entries()
+    {
+        var info = new ClientTraceInfo();
+        info.TraceEnabled = true;
+
+        info.TraceLogCount.ShouldBe(0);
+
+        info.TraceMsgDelivery("x", "dest-x", 5);
+        info.TraceMsgDelivery("y", "dest-y", 15);
+        info.TraceMsgDelivery("z", "dest-z", 25);
+
+        info.TraceLogCount.ShouldBe(3);
+
+        info.DrainTraceLog();
+
+        info.TraceLogCount.ShouldBe(0);
+    }
+}