Working on "Join Game" feature.

Shogi.UI/Pages/Home/GameBoard/SeatedGameBoard.razor

@@ -1,14 +1,22 @@
 @using Shogi.Contracts.Api;
 @using Shogi.Contracts.Types;
 @using System.Text.RegularExpressions;
+@using System.Net;
 @inject PromotePrompt PromotePrompt;
 @inject IShogiApi ShogiApi;
 
-<GameBoardPresentation OnClickHand="OnClickHand" OnClickTile="OnClickTile" Session="Session" Perspective="Perspective" />
+<GameBoardPresentation Session="Session"
+                       Perspective="Perspective"
+                       OnClickHand="OnClickHand"
+                       OnClickTile="OnClickTile"
+                       OnClickJoinGame="OnClickJoinGame" />
 
 @code {
-    [Parameter] public WhichPlayer Perspective { get; set; }
-    [Parameter] public Session Session { get; set; }
+    [Parameter, EditorRequired]
+    public WhichPlayer Perspective { get; set; }
+    [Parameter, EditorRequired]
+    public Session Session { get; set; }
+    [Parameter] public Func<Task>? OnRefetchSession { get; set; }
     private bool IsMyTurn => Session?.BoardState.WhoseTurn == Perspective;
     private string? selectedBoardPosition;
     private WhichPiece? selectedPieceFromHand;
@@ -26,7 +34,7 @@
         return false;
     }
 
-    async void OnClickTile(Piece? piece, string position)
+    async Task OnClickTile(Piece? piece, string position)
     {
         if (!IsMyTurn) return;
 
@@ -64,8 +72,21 @@
         }
     }
 
-    void OnClickHand(Piece piece)
+    async Task OnClickHand(Piece piece)
     {
         selectedPieceFromHand = piece.WhichPiece;
+        await Task.CompletedTask;
+    }
+
+    async Task OnClickJoinGame()
+    {
+        if (Session != null && OnRefetchSession != null)
+        {
+            var status = await ShogiApi.PatchJoinGame(Session.SessionName);
+            if (status == HttpStatusCode.OK)
+            {
+                await OnRefetchSession.Invoke();
+            }
+        }
     }
 }