Add teacher microphone and per-question model selection

tests/unit/coding-teacher.test.ts

@@ -103,6 +103,7 @@ async function fixture({ durableSource = false, sourceContext = context, liveMod
   const prepareCloud = vi.fn((..._args: unknown[]) => ({ inputLimit: 8000, run }));
   const createService = () => new CodingTeacherService({
     projects,
+    models: async () => ({ supported: true, models: [{ id: 'qwen' }, { id: 'other-model' }] }),
     runtime: new InMemoryConversationRuntime(),
     userDataDir: root,
     account: async () => account,
@@ -1659,3 +1660,22 @@ describe('project consultations with selected cloud teachers', () => {
     await vi.waitFor(async () => expect((await f.service.read(scope, topic.id)).requests[0].status).toBe('completed'));
   });
 });
+
+ it.each([false, true])('freezes explicit model without changing teacher definition (cloud=%s)', async cloudTeacher => {
+    const f = await fixture({ cloudTeacher, mockCloud: cloudTeacher });
+    const t = await f.service.create(f.scope, undefined, undefined, cloudTeacher ? 9 : undefined);
+    const input = { requestId: '22222222-2222-4222-8222-222222222222', text: '帮我理解', modelId: 'other-model' };
+    const accepted = await f.service.send(f.scope, t.id, input);
+    expect(accepted.requests[0].modelId).toBe('other-model');
+    expect(accepted.definition.model.model_id).toBe('qwen');
+    if (!cloudTeacher) expect(f.prepareModel.mock.calls[0][1].model).toEqual({ model_id: 'other-model', reasoning_choice: { mode: 'default' } });
+    await expect(f.service.send(f.scope, t.id, { ...input, modelId: 'qwen' })).rejects.toMatchObject({ code: 'teacher_request_conflict' });
+    await f.service.send(f.scope, t.id, input);
+    expect(f.run).toHaveBeenCalledTimes(1);
+    f.finish();
+    await vi.waitFor(async () => expect((await f.service.read(f.scope, t.id)).requests[0].status).toBe('completed'));
+    const restarted = await f.restart();
+    expect((await restarted.read(f.scope, t.id)).requests[0].modelId).toBe('other-model');
+    await expect(restarted.send(f.scope, t.id, { ...input, requestId: '33333333-3333-4333-8333-333333333333', modelId: 'unavailable' })).rejects.toMatchObject({ code: 'teacher_model_unavailable' });
+    expect(f.run).toHaveBeenCalledTimes(1);
+ });