yep

Shogi.Api/Controllers/SessionsController.cs

@@ -77,6 +77,11 @@ public class SessionsController : ControllerBase
         return Ok(await this.queryRespository.ReadSessionPlayerCount(this.User.GetShogiUserId()));
     }
 
+    /// <summary>
+    /// Fetch the session and latest board state. Also subscribe the user to socket events for this session.
+    /// </summary>
+    /// <param name="name"></param>
+    /// <returns></returns>
     [HttpGet("{name}")]
     public async Task<ActionResult<ReadSessionResponse>> GetSession(string name)
     {
@@ -113,6 +118,7 @@ public class SessionsController : ControllerBase
             session.AddPlayer2(User.GetShogiUserId());
 
             await sessionRepository.SetPlayer2(name, User.GetShogiUserId());
+            await communicationManager.BroadcastToAll(new SessionJoinedByPlayerSocketMessage());
             return this.Ok();
         }
         return this.Conflict("This game already has two players.");
@@ -144,6 +150,8 @@ public class SessionsController : ControllerBase
             return this.Conflict(e.Message);
         }
         await sessionRepository.CreateMove(sessionName, command);
+
+        // Send socket message to both players so their clients know that new board state is available.
         await communicationManager.BroadcastToPlayers(
           new PlayerHasMovedMessage
           {