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backend/F9WebAiTest.Api/Hubs/NotificationHub.cs

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+using System.Collections.Concurrent;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.SignalR;
+
+namespace F9WebAiTest.Api.Hubs;
+
+/// <summary>在线用户登记表（用于判断用户是否在线，离线则走"拉取兜底"）</summary>
+public static class OnlineUserRegistry
+{
+    private static readonly ConcurrentDictionary<long, byte> _users = new();
+
+    public static void Add(long userId) => _users[userId] = 0;
+
+    public static void Remove(long userId) => _users.TryRemove(userId, out _);
+
+    public static bool IsOnline(long userId) => _users.ContainsKey(userId);
+}
+
+/// <summary>通知推送 Hub（客户端连接后按 UserId 标识，服务端用 Clients.User(userId) 定向推送）</summary>
+public class NotificationHub : Hub
+{
+    public override async Task OnConnectedAsync()
+    {
+        var userId = GetUserId();
+        if (userId > 0) OnlineUserRegistry.Add(userId);
+        await base.OnConnectedAsync();
+    }
+    public override async Task OnDisconnectedAsync(Exception exception)
+    {
+        var userId = GetUserId();
+        if (userId > 0) OnlineUserRegistry.Remove(userId);
+        await base.OnDisconnectedAsync(exception);
+    }
+
+    private long GetUserId()
+    {
+        var raw = Context.User?.FindFirst("id")?.Value;
+        return long.TryParse(raw, out var id) ? id : 0;
+    }
+}
+
+/// <summary>自定义用户标识：使用 JWT 中的 "id" 声明作为 SignalR 的 UserIdentifier</summary>
+public class NotificationUserIdProvider : IUserIdProvider
+{
+    public string GetUserId(HubConnectionContext connection)
+        => connection.User?.FindFirst("id")?.Value ?? connection.ConnectionId;
+}