feat(iios): notification engine — presence-gated Web Push (engine phase)

Generic notification engine: reacts to message.sent and runs three gates before
delivering — policy (DM always; group only on @mention or reply-to-you), presence
(skip if the recipient is focused on that thread), mute (per-thread). Delivery via a
swappable NotificationPort (Web Push/VAPID adapter); a 'gone' (404/410) prunes the sub.

- PresenceService + gateway `focus_thread` signal + disconnect cleanup (room membership
  != viewing, since the sidebar joins every thread room).
- IiosNotificationSubscription table + `muted` on IiosThreadParticipant (migration).
- Endpoints: GET vapid-public-key, POST/DELETE subscribe, POST threads/:id/mute|unmute;
  listThreads returns the caller's `muted`.
- DM-vs-group read from the opaque `membership` attribute in the notification POLICY only
  — kernel stays generic (grep-verified).

Tests: 13 new (3 gates + reply-to-you + prune + web-push adapter states); full suite 205
green. Verified live: module boots, subscribe stored, mute/unmute round-trips.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/iios-service/src/messaging/message.gateway.ts

@@ -4,6 +4,7 @@ import {
   ConnectedSocket,
   MessageBody,
   OnGatewayConnection,
+  OnGatewayDisconnect,
   OnGatewayInit,
   SubscribeMessage,
   WebSocketGateway,
@@ -15,6 +16,7 @@ import { logJson } from '../observability/logger';
 import { MessageService, type MessagePrincipal } from './message.service';
 import { SessionVerifier } from '../platform/session.verifier';
 import { OutboxBus } from '../outbox/outbox.bus';
+import { PresenceService } from '../notifications/presence.service';
 
 interface SocketState {
   principal: MessagePrincipal;
@@ -27,7 +29,7 @@ interface SocketState {
  * propagates messages persisted elsewhere (REST/ingest) to connected clients.
  */
 @WebSocketGateway({ namespace: '/message', cors: { origin: true } })
-export class MessageGateway implements OnGatewayInit, OnGatewayConnection {
+export class MessageGateway implements OnGatewayInit, OnGatewayConnection, OnGatewayDisconnect {
   private readonly logger = new Logger(MessageGateway.name);
   private readonly emittedLocally = new Set<string>();
 
@@ -37,6 +39,7 @@ export class MessageGateway implements OnGatewayInit, OnGatewayConnection {
     private readonly messages: MessageService,
     private readonly session: SessionVerifier,
     private readonly bus: OutboxBus,
+    private readonly presence: PresenceService,
   ) {}
 
   afterInit(): void {
@@ -65,6 +68,18 @@ export class MessageGateway implements OnGatewayInit, OnGatewayConnection {
     }
   }
 
+  handleDisconnect(client: Socket): void {
+    this.presence.clearSocket(client.id);
+  }
+
+  /** The app reports which thread is in the foreground (or null when blurred) — presence. */
+  @SubscribeMessage('focus_thread')
+  focusThread(@ConnectedSocket() client: Socket, @MessageBody() body: { threadId: string | null }): void {
+    const state = client.data as SocketState | undefined;
+    if (!state?.principal) return;
+    this.presence.setFocus(client.id, state.principal.userId, body?.threadId ?? null);
+  }
+
   @SubscribeMessage('open_thread')
   async openThread(@ConnectedSocket() client: Socket, @MessageBody() body: { threadId?: string; membership?: string; creatorRole?: string; subject?: string }) {
     const { principal } = client.data as SocketState;