test(12-07): add MockAgentManager decompose mode tests

Add tests for decompose mode scenarios:
- Spawn agent in decompose mode
- Complete with tasks on decompose_complete
- Pause on questions in decompose mode
- Emit stopped event with decompose_complete reason
- Set result message with task count

src/agent/mock-manager.test.ts

@@ -687,6 +687,97 @@ describe('MockAgentManager', () => {
     });
   });
 
+  // ===========================================================================
+  // Decompose mode (plan to tasks)
+  // ===========================================================================
+
+  describe('decompose mode', () => {
+    it('should spawn agent in decompose mode', async () => {
+      const agent = await manager.spawn({
+        name: 'decomposer',
+        taskId: 'plan-1',
+        prompt: 'Decompose this plan',
+        mode: 'decompose',
+      });
+      expect(agent.mode).toBe('decompose');
+    });
+
+    it('should complete with tasks on decompose_complete', async () => {
+      manager.setScenario('decomposer', {
+        status: 'decompose_complete',
+        tasks: [
+          { number: 1, name: 'Task 1', description: 'First task', type: 'auto', dependencies: [] },
+          { number: 2, name: 'Task 2', description: 'Second task', type: 'auto', dependencies: [1] },
+        ],
+      });
+
+      await manager.spawn({ name: 'decomposer', taskId: 'plan-1', prompt: 'test', mode: 'decompose' });
+      await vi.advanceTimersByTimeAsync(100);
+
+      // Verify agent:stopped event with decompose_complete reason
+      const stoppedEvent = eventBus.emittedEvents.find((e) => e.type === 'agent:stopped') as AgentStoppedEvent | undefined;
+      expect(stoppedEvent).toBeDefined();
+      expect(stoppedEvent?.payload.reason).toBe('decompose_complete');
+    });
+
+    it('should pause on questions in decompose mode', async () => {
+      manager.setScenario('decomposer', {
+        status: 'questions',
+        questions: [{ id: 'q1', question: 'How many tasks?' }],
+      });
+
+      await manager.spawn({ name: 'decomposer', taskId: 'plan-1', prompt: 'test', mode: 'decompose' });
+      await vi.advanceTimersByTimeAsync(100);
+
+      // Verify agent pauses for questions
+      const stoppedEvent = eventBus.emittedEvents.find((e) => e.type === 'agent:waiting');
+      expect(stoppedEvent).toBeDefined();
+
+      // Check agent status
+      const agent = await manager.getByName('decomposer');
+      expect(agent?.status).toBe('waiting_for_input');
+    });
+
+    it('should emit stopped event with decompose_complete reason', async () => {
+      manager.setScenario('decompose-done', {
+        status: 'decompose_complete',
+        delay: 0,
+        tasks: [
+          { number: 1, name: 'Setup', description: 'Initial setup', type: 'auto', dependencies: [] },
+        ],
+      });
+
+      await manager.spawn({
+        name: 'decompose-done',
+        taskId: 'plan-1',
+        prompt: 'test',
+        mode: 'decompose',
+      });
+      await vi.runAllTimersAsync();
+
+      const stopped = eventBus.emittedEvents.find((e) => e.type === 'agent:stopped') as AgentStoppedEvent | undefined;
+      expect(stopped?.payload.reason).toBe('decompose_complete');
+    });
+
+    it('should set result message with task count', async () => {
+      manager.setScenario('decomposer', {
+        status: 'decompose_complete',
+        tasks: [
+          { number: 1, name: 'Task 1', description: 'First', type: 'auto', dependencies: [] },
+          { number: 2, name: 'Task 2', description: 'Second', type: 'checkpoint:human-verify', dependencies: [1] },
+          { number: 3, name: 'Task 3', description: 'Third', type: 'auto', dependencies: [1, 2] },
+        ],
+      });
+
+      const agent = await manager.spawn({ name: 'decomposer', taskId: 'plan-1', prompt: 'test', mode: 'decompose' });
+      await vi.runAllTimersAsync();
+
+      const result = await manager.getResult(agent.id);
+      expect(result?.success).toBe(true);
+      expect(result?.message).toBe('Decomposed into 3 tasks');
+    });
+  });
+
   // ===========================================================================
   // Structured question data (new schema tests)
   // ===========================================================================