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;
+    }
+}

StarterNG/Domain/Consist.cs

@@ -324,6 +324,10 @@ public sealed class Consist : IReadOnlyList<ConsistItem>
         int gap = _items.IndexOf(item);
         _items.Remove(item);
 
+        // The car now at the end still holds the coupler of the one taken off it.
+        if (gap == _items.Count)
+            FreeTail();
+
         if (ReferenceEquals(Selected, item))
             Selected = _items.Count == 0
                 ? null
@@ -551,6 +555,8 @@ public sealed class Consist : IReadOnlyList<ConsistItem>
 
             left.Coupling.Flags = left.Coupling.Locked ? -common : common;
         }
+
+        FreeTail();
     }
 
     public bool CanFormUnit(ConsistItem left, ConsistItem right)
@@ -598,6 +604,18 @@ public sealed class Consist : IReadOnlyList<ConsistItem>
     public static Dynamic HeadCar(ConsistItem item) =>
         item.Flipped ? item.Cars[^1] : item.Cars[0];
 
+    /// <summary>
+    /// Clears the coupler at the back of the consist. The simulator hangs the end
+    /// signals only on a last vehicle whose coupler is 0 - anything else couples it
+    /// to whatever stands behind - and every new car comes with 3. Its parameters,
+    /// the brake setting among them, stay.
+    /// </summary>
+    private void FreeTail()
+    {
+        if (_items.Count > 0 && _items[^1].Cars.Count > 0)
+            TailCar(_items[^1]).Coupling.Flags = 0;
+    }
+
     /// <summary>
     /// Whether a car runs turned. Its own sign is the truth - it is what the export
     /// writes - and decides which coupler is at which end; a card's flag agrees

StarterNG/Views/Depot/VehicleDetails.cs

@@ -179,6 +179,8 @@ public sealed class VehicleDetails
             return;
 
         bool isLast = unitIdx >= _consist.Count - 1;
+        if (isLast)
+            couplerPanel.Children.Add(PanelNote(App.Loc["CouplingLastNote"]));
 
         var d = Consist.TailCar(item);
 

StarterNG/startercfg/lang/cz.xml

@@ -280,6 +280,7 @@
     <String key="TipSplit">Rozdělit jednotku na jednotlivé vozy</String>
     <String key="AppliesToUnit">Společné pro celou jednotku</String>
     <String key="CouplingUnitRear">Spřáhlo na konci jednotky</String>
+    <String key="CouplingLastNote">Poslední vozidlo: spřáhlo 0 dává koncovky. Jiný kód spojí soupravu s tím, co stojí za ní, a simulátor koncovky nenasadí.</String>
     <String key="Join">Spojit</String>
     <String key="TipJoin">Spojit toto vozidlo s následujícím do jedné jednotky</String>
     <String key="TipReorder">Přetáhněte pro změnu pořadí</String>

StarterNG/startercfg/lang/en.xml

@@ -280,6 +280,7 @@
     <String key="TipSplit">Split the unit into individual cars</String>
     <String key="AppliesToUnit">Shared by the whole unit</String>
     <String key="CouplingUnitRear">Coupler at the rear of the unit</String>
+    <String key="CouplingLastNote">Last vehicle: coupler 0 gets the end signals. Any other code couples the train to whatever stands behind it, and the simulator puts up no end signals.</String>
     <String key="Join">Join</String>
     <String key="TipJoin">Couple this vehicle with the next one into a single unit</String>
     <String key="TipReorder">Drag to reorder</String>

StarterNG/startercfg/lang/hu.xml

@@ -280,6 +280,7 @@
     <String key="TipSplit">Az egység szétbontása külön kocsikra</String>
     <String key="AppliesToUnit">Az egész egységre közös</String>
     <String key="CouplingUnitRear">Az egység végén lévő kapcsolókészülék</String>
+    <String key="CouplingLastNote">Utolsó jármű: a 0-s kapcsolat adja a zárjelzőket. Más kód a mögötte álló járműhöz kapcsolja a szerelvényt, és a szimulátor nem tesz fel zárjelzőt.</String>
     <String key="Join">Összekapcsolás</String>
     <String key="TipJoin">A jármű összekapcsolása a következővel egy egységgé</String>
     <String key="TipReorder">Húzza az átrendezéshez</String>

StarterNG/startercfg/lang/pl.xml

@@ -280,6 +280,7 @@
     <String key="TipSplit">Rozdziel zespół na pojedyncze człony</String>
     <String key="AppliesToUnit">Ustawienie wspólne dla całego zespołu</String>
     <String key="CouplingUnitRear">Sprzęg na końcu zespołu</String>
+    <String key="CouplingLastNote">Ostatni pojazd: sprzęg 0 daje końcówki. Inny kod połączy skład z tym, co stoi za nim, a symulator nie założy końcówek.</String>
     <String key="Join">Złącz</String>
     <String key="TipJoin">Połącz ten pojazd z następnym w jeden zespół</String>
     <String key="TipReorder">Przeciągnij, aby zmienić kolejność</String>

StarterNG/startercfg/lang/ru.xml

@@ -280,6 +280,7 @@
     <String key="TipSplit">Разделить сцеп на отдельные вагоны</String>
     <String key="AppliesToUnit">Общее для всего состава</String>
     <String key="CouplingUnitRear">Сцепка в конце состава</String>
+    <String key="CouplingLastNote">Последняя единица: сцепка 0 даёт хвостовые сигналы. Другой код сцепит состав с тем, что стоит за ним, и симулятор не поставит хвостовые сигналы.</String>
     <String key="Join">Соединить</String>
     <String key="TipJoin">Соединить этот вагон со следующим в один состав</String>
     <String key="TipReorder">Перетащите для изменения порядка</String>