feat(realtime): push channel.joined/left events to user-scoped rooms

Backend half of the plugin push-based channel sync (companion to
nav/Fabric.OpenclawPlugin#1 follow-up). Before this, the OpenClaw
fabric inbound had to poll `/api/channels?guildId=...` every 60s to
discover newly-joined channels (any DM another user just dragged the
agent into). Now the server tells the agent's socket directly so
sub/unsub is realtime.

Changes:
- realtime.gateway.ts:
  * handleConnection joins the socket into a `user:<userId>` room.
    All of a user's connected sockets now share that room.
  * New `emitToUser(userId, event, data)` helper that emits into
    that room. No-op for offline users (next connect resyncs via the
    plugin's initial channel-list fetch).
- channels.service.ts:
  * Inject RealtimeGateway (RealtimeModule is @Global, no module
    plumbing needed).
  * Private `notifyMembership(kind, channelId, userIds, extra)`
    helper that emits `channel.<kind>` (joined|left) with payload
    {channelId, userId, xType, occurredAt}.
  * create(): emit channel.joined to every seeded member (creator +
    explicit memberUserIds + triage on-duty).
  * joinChannel(): emit channel.joined to userId (only if the row was
    actually inserted, idempotent on existing membership).
  * leaveChannel(): emit channel.left to userId iff a row was
    actually deleted.

Event shape:
  {
    channelId: string,
    userId: string,
    xType?: string,
    occurredAt: ISO string,
  }

Client-side contract (fabric plugin):
  socket.on('channel.joined', m => socket.emit('join_channel', {channelId: m.channelId}))
  socket.on('channel.left',   m => socket.emit('leave_channel', {channelId: m.channelId}))

The plugin keeps its 60s polling resync as a safety net for missed
events (transient socket drops between emit and reconnect, partial
failures, etc).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/channels/channels.service.ts

@@ -5,6 +5,7 @@ import { Channel } from '../entities/channel.entity.js';
 import { ChannelMember } from '../entities/channel-member.entity.js';
 import { WakeMapping } from '../entities/wake-mapping.entity.js';
 import { TurnService } from './turn.service.js';
+import { RealtimeGateway } from '../realtime/realtime.gateway.js';
 
 const X_TYPES = ['general', 'work', 'report', 'discuss', 'triage', 'custom', 'dm'] as const;
 type XType = (typeof X_TYPES)[number];
@@ -35,8 +36,34 @@ export class ChannelsService {
     @InjectRepository(WakeMapping)
     private readonly wakeRepo: Repository<WakeMapping>,
     private readonly turnService: TurnService,
+    // RealtimeGateway is provided by the global RealtimeModule. Used to
+    // push channel.joined / channel.left so connected clients (e.g. the
+    // OpenClaw fabric plugin) can sub/unsub socket.io rooms immediately
+    // instead of waiting for the polling fallback.
+    private readonly realtime: RealtimeGateway,
   ) {}
 
+  // Push a channel membership change to each affected user's socket-room.
+  // Best-effort: offline users see the new state on their next connect
+  // (the inbound runs an initial channel-list fetch on connect).
+  private notifyMembership(
+    kind: 'joined' | 'left',
+    channelId: string,
+    userIds: string[] | Set<string>,
+    extra: Record<string, unknown> = {},
+  ): void {
+    const ids = userIds instanceof Set ? [...userIds] : userIds;
+    const payload = {
+      channelId,
+      ...extra,
+      occurredAt: new Date().toISOString(),
+    };
+    for (const u of ids) {
+      if (!u) continue;
+      this.realtime.emitToUser(u, `channel.${kind}`, { ...payload, userId: u });
+    }
+  }
+
   // Channels visible to a user within a guild:
   //  - every public channel of the guild (incl. ones created before the user
   //    joined the guild), OR
@@ -93,6 +120,7 @@ export class ChannelsService {
       if (channel.xType === 'discuss' || channel.xType === 'work') {
         await this.turnService.onMemberAdded(channelId, userId);
       }
+      this.notifyMembership('joined', channelId, [userId], { xType: channel.xType });
     }
     return { status: 'ok', channelId, userId, member: true };
   }
@@ -102,11 +130,14 @@ export class ChannelsService {
     if (!channel) throw new NotFoundException('channel not found');
 
     // remove every channel-scoped row that references this user
-    await this.memberRepo.delete({ channelId, userId });
+    const deleted = await this.memberRepo.delete({ channelId, userId });
     await this.wakeRepo.delete({ channelId, userId });
     if (channel.xType === 'discuss' || channel.xType === 'work') {
       await this.turnService.onMemberRemoved(channelId, userId);
     }
+    if ((deleted.affected ?? 0) > 0) {
+      this.notifyMembership('left', channelId, [userId], { xType: channel.xType });
+    }
     return { status: 'ok', channelId, userId, member: false };
   }
 
@@ -160,6 +191,12 @@ export class ChannelsService {
       [...memberIds].map((userId) => this.memberRepo.create({ channelId: channel.id, userId })),
     );
 
+    // Push channel.joined to every seeded member (creator + invitees +
+    // triage on-duty) so their connected sockets sub the new room
+    // immediately. Skips offline users — next connect's channel-list
+    // fetch covers them.
+    this.notifyMembership('joined', channel.id, memberIds, { xType });
+
     // wake_mapping: triage -> the on-duty user; custom -> each listener
     const wakeUserIds = new Set<string>();
     if (xType === 'triage') wakeUserIds.add(onDuty);

src/realtime/realtime.gateway.ts

@@ -96,6 +96,10 @@ export class RealtimeGateway implements OnGatewayConnection, OnGatewayDisconnect
     const userId = result.user.id || this.userIdFromClient(client);
     client.data.userId = userId;
     this.onlineUsers.add(userId);
+    // Per-user room: lets server code emit user-scoped events (e.g.
+    // channel.joined when membership changes) without bookkeeping a
+    // userId→sockets map. All of this user's sockets receive the event.
+    client.join(`user:${userId}`);
     this.server.emit('presence.online', {
       userId,
       onlineCount: this.onlineUsers.size,
@@ -171,6 +175,14 @@ export class RealtimeGateway implements OnGatewayConnection, OnGatewayDisconnect
     this.server.to(`channel:${channelId}`).emit(event, data);
   }
 
+  // Emit a user-scoped event to all sockets currently connected for `userId`
+  // (via the `user:<userId>` room joined in handleConnection). No-op for
+  // offline users — the next connect's initial channel-list fetch covers it.
+  emitToUser(userId: string, event: string, data: Record<string, unknown>): void {
+    if (!userId) return;
+    this.server.to(`user:${userId}`).emit(event, data);
+  }
+
   // Emits message.created per-recipient so each carries its own `wakeup` flag.
   async emitMessageCreated(
     channelId: string,