Add Broadcasting (SignalR server + @simplemodule/echo client)

[antosubash]

Background

There is no way to push real-time events from server to browser. Modules cannot do live notifications, live dashboards, presence, or collaborative UI. Laravel Broadcasting + Echo solves this with private/presence channels and event-driven push (Pusher / Reverb / Soketi).

Motivation

• Notifications module wants to push the bell-icon counter live (issue Add Notifications module (multi-channel: mail / db / SMS / Slack / push) #158)
• Pulse / Horizon dashboards want live-updating charts
• Tenancy + collaborative features (e.g. document editing) need it

Design sketch

Server: SignalR hub BroadcastHub mounted at /hub/broadcast.

public interface IBroadcaster
{
 Task ToChannelAsync(string channel, string @event, object payload, CancellationToken ct);
 Task ToUserAsync(string userId, string @event, object payload, CancellationToken ct);
 Task ToTenantAsync(string tenantId, string @event, object payload, CancellationToken ct);
}

[BroadcastEvent("orders.created")]
public sealed record OrderCreatedEvent(Guid OrderId, Guid TenantId) : IBroadcastEvent
{
 public string Channel(IBroadcastContext ctx) => $"tenants.{TenantId}.orders";
}

• Bridge from IEventBus: any event marked [BroadcastEvent] is automatically forwarded to subscribers
• Channel authorization: IBroadcastChannelAuthorizer per channel (hub callback validates ClaimsPrincipal before allowing subscription)
• Presence channels: server tracks members, broadcasts join/leave
• Private channels: same as public, but require explicit auth

Client (packages/echo):

import { useChannel } from '@simplemodule/echo';
useChannel('tenants.123.orders').on('orders.created', (e) => { ... });

• Built on @microsoft/signalr; auto-reconnect; backoff; auth via current Inertia session cookie

Acceptance criteria

• IBroadcaster + BroadcastHub in framework
• [BroadcastEvent] discovered by source generator; bridge from IEventBus
• Channel authorizer pattern with at least one example
• Presence channel implementation
• @simplemodule/echo package with useChannel / useEvent hooks
• xUnit + integration tests
• Demo: live notification bell in template app
• Docs page

References

• Laravel Broadcasting: https://laravel.com/docs/broadcasting
• Laravel Echo: https://laravel.com/docs/broadcasting#client-side-installation
• ASP.NET SignalR: https://learn.microsoft.com/aspnet/core/signalr/introduction