feat(threads): governed group settings — rename, list members, remove participant

- MessageService.renameThread / removeParticipant / listParticipants,
  each fail-closed via OPA (kernel stays generic — no dm/group branching)
- dev OPA: iios.thread.update + iios.thread.participant.remove rules
  (group requires ADMIN; ungoverned threads unchanged)
- REST: PATCH /v1/threads/:id, GET + DELETE /v1/threads/:id/participants
- tests: admin renames/removes, member is denied, member list carries roles
  (message.spec + dev-opa.port.spec)

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

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

@@ -124,6 +124,28 @@ describe('Governed membership + replies (v1.1, policy-enforced)', () => {
     await expect(s.addParticipant(threadId, bob, 'carol')).rejects.toBeInstanceOf(PolicyDeniedError); // bob is MEMBER
   });
 
+  it('group settings: admin renames + lists members + removes; a plain member cannot rename/remove', async () => {
+    const s = gov();
+    const { threadId } = await s.openThread(null, alice, { membership: 'group', creatorRole: 'ADMIN', subject: 'Design' });
+    await s.addParticipant(threadId, alice, 'bob');
+
+    // admin renames
+    expect((await s.renameThread(threadId, alice, 'Design Team')).subject).toBe('Design Team');
+    // a plain member cannot rename
+    await expect(s.renameThread(threadId, bob, 'Hacked')).rejects.toBeInstanceOf(PolicyDeniedError);
+
+    // member list carries roles
+    const members = await s.listParticipants(threadId, alice);
+    expect(members.map((m) => m.userId).sort()).toEqual(['alice', 'bob']);
+    expect(members.find((m) => m.userId === 'alice')?.role).toBe('ADMIN');
+
+    // a plain member cannot remove
+    await expect(s.removeParticipant(threadId, bob, 'alice')).rejects.toBeInstanceOf(PolicyDeniedError);
+    // admin removes bob
+    expect((await s.removeParticipant(threadId, alice, 'bob')).participantCount).toBe(1);
+    expect(await prisma.iiosThreadParticipant.count({ where: { threadId } })).toBe(1);
+  });
+
   it('self-join is governed: a non-member cannot open a thread by id; after being added, they can', async () => {
     const s = gov();
     const { threadId } = await s.openThread(null, alice, { membership: 'group', creatorRole: 'ADMIN' });