Add a test proving guard also protects a rear-guard from retirement

server/tests/Vanguard.Rules.Tests/GameEngineTests.cs

@@ -608,6 +608,22 @@ public class GameEngineTests
         Assert.Equal(14000, engine.EffectivePower(alfred));
     }
 
+    [Fact]
+    public void Guard_Protects_RearGuard_From_Retirement()
+    {
+        var engine = ReadyToAttackRearGuard();
+        Give(engine, 1, Barcgal);
+
+        Assert.True(engine.Execute(new AttackCommand(3, 0)).Accepted);
+        Assert.True(engine.Execute(new GuardCommand(Barcgal)).Accepted);
+        Assert.True(engine.Execute(new PassGuardCommand()).Accepted);
+
+        var defender = engine.State.Players[1];
+        Assert.NotNull(defender.RearGuards[0]);
+        Assert.Contains(defender.Drop, c => c.PrintingId == Barcgal);
+        Assert.DoesNotContain(engine.Events, e => e is UnitRetiredEvent);
+    }
+
     [Fact]
     public void ResolveTrigger_Rejects_When_Nothing_Is_Pending()
     {