Yep

Shogi.Domain/ValueObjects/ShogiBoard.cs

@@ -91,6 +91,11 @@ public sealed class ShogiBoard(BoardState initialState)
 
 	public MoveResult Move(WhichPiece pieceInHand, string to)
 	{
+		if (BoardState.IsCheckmate)
+		{
+			return new MoveResult(false, "The game is over. A winner has been decided.");
+		}
+
 		var index = BoardState.ActivePlayerHand.FindIndex(p => p.WhichPiece == pieceInHand);
 		if (index == -1)
 		{
@@ -250,7 +255,8 @@ public sealed class ShogiBoard(BoardState initialState)
 							list.Add(position);
 							position += path.Step;
 						}
-					} else if (position.IsInsideBoardBoundary())
+					}
+					else if (position.IsInsideBoardBoundary())
 					{
 						list.Add(position);
 					}