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-messaging-ui/src/adapters/kernel-client.test.ts

@@ -3,6 +3,7 @@
 // layer is faked (via kernel-client's own SocketLike seam), so the facade's wire mapping is
 // exercised for real. No live IIOS required.
 
+import { describe, it, expect } from 'vitest';
 import { MessageSocket } from '@insignia/iios-kernel-client';
 import type { Message as KernelMessage, SocketLike } from '@insignia/iios-kernel-client';
 import { runAdapterConformance } from '../conformance';
@@ -113,6 +114,20 @@ function makeFakeRest(): RestPort {
     async addParticipant() {
       /* governed server-side; a fake always allows */
     },
+    async discoverThreads() {
+      return [
+        {
+          threadId: 'th_pub',
+          subject: 'general',
+          metadata: { membership: 'channel', visibility: 'public', topic: 'Company-wide' },
+          participantCount: 3,
+          joined: false,
+        },
+      ];
+    },
+    async leaveThread(threadId) {
+      return { threadId, participantCount: 0 };
+    },
   };
 }
 
@@ -122,3 +137,17 @@ function makeAdapter(): KernelClientAdapter {
 }
 
 runAdapterConformance({ makeAdapter, seededThreadId: SEEDED, openWith: ['pp_a'] });
+
+describe('KernelClientAdapter channels', () => {
+  it('browse maps discovered public channels; create/join/leave delegate to the transport', async () => {
+    const adapter = makeAdapter();
+    const list = await adapter.browseChannels!();
+    expect(list[0]).toMatchObject({ threadId: 'th_pub', name: 'general', visibility: 'public', joined: false, memberCount: 3, topic: 'Company-wide' });
+
+    const { threadId } = await adapter.createChannel!({ name: 'design', topic: 'UI', visibility: 'public' });
+    expect(typeof threadId).toBe('string');
+
+    await expect(adapter.joinChannel!('th_pub')).resolves.toBeUndefined();
+    await expect(adapter.leaveChannel!('th_pub')).resolves.toBeUndefined();
+  });
+});