fix(chat): KeyNotFoundException dans HubConnectionManager.OnConnected

ChatUserNames n'etait jamais alimente (relique d'un SetUserName disparu),
ce qui faisait lever KeyNotFoundException a chaque connexion SignalR et
fermait immediatement la connexion cote client ("Déconnecté (The server
closed the connection...)" dans PostIt).

- IConnexionManager.OnConnected prend desormais le userName en parametre
- HubConnectionManager.OnConnected alimente ChatUserNames et ChatCxIds
- ChatHub.OnConnectedAsync passe le userName resolu depuis les claims

Inclut aussi les changements PostIt lies (bandeau de statut avec
commande d'action, handlers Reconnecting/Reconnected/Closed).

src/PostIt/PostIt/Controls/StatusBar.axaml

@@ -18,6 +18,7 @@
               TextWrapping="Wrap"
               VerticalAlignment="Center"/>
             <Button Content="{Binding CheckCommandLabel}"
+                Foreground="{Binding Foreground}"
                     VerticalAlignment="Center"
                     IsVisible="{Binding HasCheckCommand}"
                     Command="{Binding CheckCommand}"

src/PostIt/PostIt/ViewModels/Chat/ChatViewModel.cs

@@ -148,6 +148,41 @@ namespace PostIt.ViewModels.Chat
                 await _connection.StartAsync();
                 IsConnected = true;
                 Status = new StatusNotice("Connecté au Hub SignalR", StatusSeverity.Info, new RelayCheckCommand("Déconnecter", async () => await DisconnectAsync()));
+
+                // WithAutomaticReconnect ne lève pas d'exception en cas de
+                // perte réseau : l'état passe par Reconnecting/Closed. Sans
+                // ces handlers, IsConnected resterait optimiste et Join()
+                // échouerait avec "connection is not active".
+                _connection.Reconnecting += error =>
+                {
+                    Avalonia.Threading.Dispatcher.UIThread.Post(() =>
+                    {
+                        IsConnected = false;
+                        Status = new StatusNotice($"Connexion perdue ({error?.Message ?? "réseau"}), reconnexion...", StatusSeverity.Error,
+                            new RelayCheckCommand("Déconnecter", async () => await DisconnectAsync()));
+                    });
+                    return Task.CompletedTask;
+                };
+                _connection.Reconnected += _ =>
+                {
+                    Avalonia.Threading.Dispatcher.UIThread.Post(() =>
+                    {
+                        IsConnected = true;
+                        Status = new StatusNotice("Reconnecté au Hub SignalR", StatusSeverity.Info,
+                            new RelayCheckCommand("Déconnecter", async () => await DisconnectAsync()));
+                    });
+                    return Task.CompletedTask;
+                };
+                _connection.Closed += error =>
+                {
+                    Avalonia.Threading.Dispatcher.UIThread.Post(() =>
+                    {
+                        IsConnected = false;
+                        Status = new StatusNotice($"Déconnecté ({error?.Message ?? "fin de connexion"})", StatusSeverity.Info,
+                            new RelayCheckCommand("Connecter", async () => await ConnectAsync()));
+                    });
+                    return Task.CompletedTask;
+                };
             }
             catch (Exception ex)
             {
@@ -156,15 +191,34 @@ namespace PostIt.ViewModels.Chat
             }
         }
 
-        private async Task CheckConnectionAsync()
+        private Task CheckConnectionAsync()
         {
-            throw new NotImplementedException();
+            var state = _connection?.State.ToString() ?? "aucune connexion";
+            Messages.Add($"État de la connexion : {state}");
+            return Task.CompletedTask;
         }
 
         private async Task JoinRoomAsync()
         {
             if (_connection == null || string.IsNullOrWhiteSpace(CurrentRoom)) return;
 
+            // InvokeCoreAsync exige une connexion active : avec la
+            // reconnexion automatique, l'état peut être Reconnecting au
+            // moment de l'appel. On tente une (re)connexion si nécessaire.
+            if (_connection.State != HubConnectionState.Connected)
+            {
+                Messages.Add($"Connexion non active ({_connection.State}), tentative de reconnexion...");
+                try
+                {
+                    await _connection.StartAsync();
+                }
+                catch (Exception ex)
+                {
+                    Messages.Add($"Reconnexion impossible : {ex.Message}");
+                    return;
+                }
+            }
+
             try
             {
                 // Appel de la méthode publique 'Join' du Hub (renvoie un ChatRoomInfo)

src/PostIt/PostIt/ViewModels/StatusNotice.cs

@@ -12,7 +12,7 @@ public sealed class StatusNotice
     public string BorderBrush { get; }
     public string Foreground { get; }
 
-    public bool HasCheckCommand { get; }
+    public bool HasCheckCommand { get => CheckCommand != null; }
 
     public ICommand? CheckCommand { get; }
 
@@ -29,12 +29,9 @@ public sealed class StatusNotice
             StatusSeverity.Warning => ("~", "#7C4A03", "#E6A700", "#eaeaea"),
             _ => ("i", "#E8F0FE", "#5B8DEF", "#1E3A8A"),
         };
-        HasCheckCommand = checkCommand != null;
         CheckCommand = checkCommand;
-        CheckCommandLabel = HasCheckCommand ? "Check" :
-            checkCommand == null ?
-                string.Empty :
-                checkCommand is IWithLabel labeled ? labeled.Label : string.Empty;
+        CheckCommandLabel = HasCheckCommand ?
+                (checkCommand is IWithLabel labeled ? labeled.Label : "Check") : string.Empty;
     }
 
     public static StatusNotice Info(string message, ICommand? checkCommand = null) => new(message, StatusSeverity.Info, checkCommand);

src/Yavsc.Server/Hubs/ChatHub.cs

@@ -90,7 +90,7 @@ namespace Yavsc.Server.Hubs
             {
                 await Groups.AddToGroupAsync(Context.ConnectionId, ChatHubConstants.HubGroupFollowingPrefix + uid);
             }
-            _cxManager.OnConnected(Context.ConnectionId, isCop);
+            _cxManager.OnConnected(Context.ConnectionId, userName, isCop);
             await base.OnConnectedAsync();
         }
 

src/Yavsc.Server/Interfaces/IConnexionManager.cs

@@ -4,7 +4,7 @@ namespace Yavsc.Services
 {
     public interface IConnexionManager {
         string GetUserName (string cxId);
-        void OnConnected(string cxId, bool isCop);
+        void OnConnected(string cxId, string userName, bool isCop);
         bool IsConnected(string candidate);
 
         void OnDisconnected (string cxId);

src/Yavsc.Server/Services/HubConnectionManager.cs

@@ -53,13 +53,15 @@ namespace Yavsc.Services
             _localizer = stringLocFactory.Create(typeof(HubConnectionManager));
         }
 
-        // Username must have been set before calling this method.
-        public void OnConnected(string cxId,  bool isCop)
+        public void OnConnected(string cxId, string userName, bool isCop)
         {
-            var username = ChatUserNames[cxId];
-            if (!IsConnected(username))
-                ChatRoomPresence[username] = new List<string>();
-            _isCop[username] = isCop;
+            ChatUserNames[cxId] = userName;
+            ChatCxIds.AddOrUpdate(userName,
+                _ => new List<string> { cxId },
+                (_, list) => { lock (list) { if (!list.Contains(cxId)) list.Add(cxId); } return list; });
+            if (!IsConnected(userName))
+                ChatRoomPresence[userName] = new List<string>();
+            _isCop[userName] = isCop;
         }
 
         public bool IsConnected(string candidate)