feat: channels on the direct-IIOS path — kernel-client + KernelClientAdapter

- iios-kernel-client: RestClient.discoverThreads (GET /v1/threads/discover) +
  leaveThread (DELETE /v1/threads/:id/me); DiscoveredThread type
- KernelClientAdapter implements the four channel methods: browseChannels maps
  discovered public channels → ChannelSummary; createChannel → createThread
  (membership=channel, ADMIN, visibility/topic metadata); joinChannel →
  socket.openThread (governed public self-join); leaveChannel → rest.leaveThread
- adapter channel test over the fake transport (13 kernel-adapter tests); 57 green

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/iios-kernel-client/src/rest.ts

@@ -1,5 +1,5 @@
 import type { IngestInteractionRequest } from '@insignia/iios-contracts';
-import type { Message, InboxItem, InboxState, Ticket, TicketState, CallbackRequest, RouteBinding, RouteDecision, AiArtifact, AiJobResult, Meeting, MeetingActionItem, ThreadSummary, SavedItem, LoginResult } from './types';
+import type { Message, InboxItem, InboxState, Ticket, TicketState, CallbackRequest, RouteBinding, RouteDecision, AiArtifact, AiJobResult, Meeting, MeetingActionItem, ThreadSummary, DiscoveredThread, SavedItem, LoginResult } from './types';
 
 export interface RestConfig {
   serviceUrl: string;
@@ -103,6 +103,27 @@ export class RestClient {
     return this.post<{ threadId: string }>('/v1/threads', opts);
   }
 
+  /**
+   * Discover threads across your scope matching an opaque metadata filter (e.g. browse public
+   * channels: `{ membership: 'channel', visibility: 'public' }`). Returns ones you have NOT joined
+   * too, each flagged `joined`.
+   */
+  async discoverThreads(filter?: { metadata?: Record<string, string> }): Promise<DiscoveredThread[]> {
+    const qs = filter?.metadata
+      ? '?' + Object.entries(filter.metadata).map(([k, v]) => `metadata[${encodeURIComponent(k)}]=${encodeURIComponent(v)}`).join('&')
+      : '';
+    const r = await fetch(this.url(`/v1/threads/discover${qs}`), { headers: this.headers() });
+    if (!r.ok) throw new Error(`discoverThreads ${r.status}`);
+    return (await r.json()) as DiscoveredThread[];
+  }
+
+  /** Self-leave a thread (e.g. leave a channel). */
+  async leaveThread(threadId: string): Promise<{ threadId: string; participantCount: number }> {
+    const r = await fetch(this.url(`/v1/threads/${threadId}/me`), { method: 'DELETE', headers: this.headers() });
+    if (!r.ok) throw new Error(`leaveThread ${r.status}`);
+    return (await r.json()) as { threadId: string; participantCount: number };
+  }
+
   /** My saved messages (personal bookmarks), newest first, with thread context. */
   async listSaved(): Promise<SavedItem[]> {
     const r = await fetch(this.url('/v1/threads/my-annotations?type=save'), { headers: this.headers() });