Leave the last vehicle's coupler at 0 so the train gets its end signals

The simulator hangs end signals only on a last vehicle with coupler 0; every
new car came with 3 and the pass that couples neighbours never touched the
last one, nor did taking a car off the end. The coupler editor says so for
the last vehicle.

StarterNG.Tests/ConsistTailTests.cs

@@ -0,0 +1,68 @@
+using StarterNG.Classes;
+using StarterNG.Domain;
+using StarterNG.Domain.Vehicles;
+using StarterNG.Tests.Fakes;
+
+namespace StarterNG.Tests;
+
+// The simulator puts end signals only on a last vehicle whose coupler is 0.
+public class ConsistTailTests
+{
+    private readonly Consist _consist;
+    private readonly VehicleCatalog _catalog;
+
+    public ConsistTailTests()
+    {
+        var installation = new TestInstallation(new InMemoryFileSystem()
+            .WithFile(TestInstallation.At("dynamic", "pkp", "b111", "textures.txt"),
+                      "!=b\nb111-01.mat=b111,B111\nb111-02.mat=b111,B111"));
+        installation.Vehicles.Load(installation.Library.Vehicles);
+        _catalog = installation.Library.Vehicles;
+        _consist = new Consist(_catalog, new VehicleInfo(_catalog, installation.Physics));
+    }
+
+    [Fact]
+    public void A_new_last_car_is_left_uncoupled_at_the_back()
+    {
+        var first = Append("b111-01");
+        var last = Append("b111-02");
+
+        _consist.AutoConnectAll();
+
+        Assert.NotEqual(0, first.Cars[0].Coupling.Flags);
+        Assert.Equal(0, last.Cars[0].Coupling.Flags);
+    }
+
+    [Fact]
+    public void Taking_off_the_last_car_frees_the_one_now_at_the_back()
+    {
+        var first = Append("b111-01");
+        var last = Append("b111-02");
+        _consist.AutoConnectAll();
+
+        _consist.Remove(last);
+
+        Assert.Equal(0, first.Cars[0].Coupling.Flags);
+    }
+
+    [Fact]
+    public void Freeing_the_back_keeps_the_brake_setting()
+    {
+        var car = Append("b111-01");
+        car.Cars[0].Coupling = Coupling.Parse("3.BP");
+
+        _consist.AutoConnectAll();
+
+        Assert.Equal("0.BP", car.Cars[0].Coupling.ToString());
+    }
+
+    private ConsistItem Append(string skin)
+    {
+        var item = new ConsistItem
+        {
+            Cars = new List<Dynamic> { _consist.MakeDynamic(_catalog.TextureForSkin(skin)!, null) }
+        };
+        _consist.Insert(_consist.Count, item);
+        return item;
+    }
+}