// Strongly-typed hub with client interface
public class RegisterHub : Hub<IRegisterHubClient>
{
    public async Task SubscribeToRegister(string registerId)
    {
        await Groups.AddToGroupAsync(Context.ConnectionId, $"register:{registerId}");
    }
}

public interface IRegisterHubClient
{
    Task RegisterCreated(string registerId, string name);
    Task TransactionConfirmed(string registerId, string transactionId);
}

public class NotificationService
{
    private readonly IHubContext<ActionsHub> _hubContext;

    public async Task NotifyActionConfirmedAsync(ActionNotification notification, CancellationToken ct)
    {
        await _hubContext.Clients
            .Group($"wallet:{notification.WalletAddress}")
            .SendAsync("ActionConfirmed", notification, ct);
    }
}

var connection = new HubConnectionBuilder()
    .WithUrl($"{baseUrl}/actionshub?access_token={jwt}")
    .Build();

connection.On<ActionNotification>("ActionConfirmed", notification => { /* handle */ });
await connection.StartAsync();
await connection.InvokeAsync("SubscribeToWallet", walletAddress);

// Interface in Services/Interfaces/
public interface INotificationService
{
    Task NotifyActionAvailableAsync(ActionNotification notification, CancellationToken ct = default);
}

// Register in DI
builder.Services.AddScoped<INotificationService, NotificationService>();

builder.Services.AddSignalR();

// Map after authentication middleware
app.MapHub<ActionsHub>("/actionshub");
app.MapHub<RegisterHub>("/hubs/register");