feat(gateway): wire safe-point runtime cancellation for agent.cancel

src/backends/native/agent.test.ts

@@ -73,6 +73,43 @@ describe('NativeAgent', () => {
     expect(mockSession.addMessage).toHaveBeenNthCalledWith(1, { role: 'user', content: 'Hi' });
     expect(mockSession.addMessage).toHaveBeenNthCalledWith(2, { role: 'assistant', content: 'Hello!' });
   });
+
+  it('supports cancellation during single-turn model wait', async () => {
+    let release!: () => void;
+    const blocked = new Promise<void>((resolve) => {
+      release = resolve;
+    });
+
+    const mockClient: ModelClient = {
+      chat: vi.fn(async () => {
+        await blocked;
+        return {
+          content: 'Late response',
+          stopReason: 'end_turn',
+          usage: { inputTokens: 10, outputTokens: 5 },
+        } satisfies ChatResponse;
+      }),
+    };
+
+    const agent = new NativeAgent({
+      modelClient: mockClient,
+      systemPrompt: 'You are helpful.',
+    });
+
+    const pending = agent.process('Please wait');
+    await new Promise<void>((resolve) => queueMicrotask(resolve));
+    expect(agent.isCancellable()).toBe(true);
+
+    agent.cancel();
+    release();
+
+    const response = await pending;
+    expect(response).toBe('Operation cancelled by user.');
+    expect(agent.isCancellable()).toBe(false);
+
+    const history = agent.getHistory();
+    expect(history[history.length - 1]).toEqual({ role: 'assistant', content: 'Operation cancelled by user.' });
+  });
 });
 
 // Simple test tool