Yep

Shogi.Api/Controllers/SessionsController.cs

@@ -67,7 +67,10 @@ public class SessionsController(
 				Player1Hand = session.Board.BoardState.Player1Hand.ToContract(),
 				Player2Hand = session.Board.BoardState.Player2Hand.ToContract(),
 				PlayerInCheck = session.Board.BoardState.InCheck?.ToContract(),
-				WhoseTurn = session.Board.BoardState.WhoseTurn.ToContract()
+				WhoseTurn = session.Board.BoardState.WhoseTurn.ToContract(),
+				Victor = session.Board.BoardState.IsCheckmate
+					? session.Board.BoardState.InCheck == Domain.ValueObjects.WhichPlayer.Player1 ? WhichPlayer.Player2 : WhichPlayer.Player1
+					: null
 			},
 			Player1 = application.GetUsername(session.Player1),
 			Player2 = application.GetUsername(session.Player2),

Shogi.Contracts/Types/BoardState.cs

@@ -1,14 +1,14 @@
 using System;
 using System.Collections.Generic;
 
-namespace Shogi.Contracts.Types
+namespace Shogi.Contracts.Types;
+
+public class BoardState
 {
-  public class BoardState
-  {
 	public Dictionary<string, Piece?> Board { get; set; } = new Dictionary<string, Piece?>();
 	public IReadOnlyCollection<Piece> Player1Hand { get; set; } = Array.Empty<Piece>();
 	public IReadOnlyCollection<Piece> Player2Hand { get; set; } = Array.Empty<Piece>();
 	public WhichPlayer? PlayerInCheck { get; set; }
 	public WhichPlayer WhoseTurn { get; set; }
-  }
+	public WhichPlayer? Victor { get; set; }
 }

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);
 					}

Shogi.UI/Pages/Play/GameBoard/GameBoardPresentation.razor

@@ -2,14 +2,6 @@
 @using System.Text.Json;
 
 <article class="game-board">
-	@if (IsSpectating)
-	{
-		<aside class="icons">
-			<div title="You are spectating.">
-				<span>Camera icon</span>
-			</div>
-		</aside>
-	}
 	<!-- Game board -->
 	<section class="board" data-perspective="@Perspective">
 		@for (var rank = 1; rank < 10; rank++)
@@ -74,13 +66,13 @@
 			</div>
 
 			<div class="place-self-center">
-				<PlayerName Name="@opponentName" IsTurn="!IsMyTurn" InCheck="IsOpponentInCheck" />
+				<PlayerName Name="@opponentName" IsTurn="!IsMyTurn" InCheck="IsOpponentInCheck" IsVictor="IsOpponentVictor" />
 				<hr />
-				<PlayerName Name="@userName" IsTurn="IsMyTurn" InCheck="IsPlayerInCheck" />
+				<PlayerName Name="@userName" IsTurn="IsMyTurn" InCheck="IsPlayerInCheck" IsVictor="IsPlayerVictor" />
 			</div>
 
 			<div class="player-area">
-				@if (string.IsNullOrEmpty(Session.Player2) && !string.IsNullOrEmpty(Session.Player1))
+				@if (Perspective == WhichPlayer.Player2 && string.IsNullOrEmpty(Session.Player2))
 				{
 					<div class="place-self-center">
 						<button @onclick="OnClickJoinGameInternal">Join Game</button>
@@ -172,6 +164,11 @@
 
 	private bool IsOpponentInCheck => Session?.BoardState.PlayerInCheck != null && Session.BoardState.PlayerInCheck != Perspective;
 
+	private bool IsPlayerVictor => Session?.BoardState.Victor == Perspective;
+
+
+	private bool IsOpponentVictor => Session?.BoardState.Victor != null && Session.BoardState.Victor != Perspective;
+
 	private Func<Task> OnClickTileInternal(string position) => () =>
 	{
 		if (IsMyTurn)

Shogi.UI/Pages/Play/GameBoard/PlayerName.razor

@@ -11,6 +11,12 @@
 		<span>&nbsp;</span>
 	}
 
+	@if (IsVictor)
+	{
+		<span class="victory-marker" title="Victory!">Victor</span>
+		<span>&nbsp;</span>
+	}
+
 	@if (string.IsNullOrEmpty(Name))
 	{
 		<span>Empty Seat</span>
@@ -25,5 +31,6 @@
 @code {
 	[Parameter][EditorRequired] public bool IsTurn { get; set; }
 	[Parameter][EditorRequired] public bool InCheck { get; set; }
+	[Parameter][EditorRequired] public bool IsVictor { get; set; }
 	[Parameter][EditorRequired] public string Name { get; set; } = string.Empty;
 }

Shogi.UI/Pages/Play/GameBoard/PlayerName.razor.css

@@ -15,3 +15,12 @@
 	font-weight: bold;
 	font-size: 80%;
 }
+
+.victory-marker {
+	display: inline-block;
+	padding: 3px 8px;
+	background-color: darkgreen;
+	color: beige;
+	font-weight: bold;
+	font-size: 80%;
+}