Improve in-flight cancel latency via run abort signal propagation

src/backends/native/agent.test.ts

@@ -24,10 +24,11 @@ describe('NativeAgent', () => {
     const response = await agent.process('Hi');
 
     expect(response).toBe('Hello!');
-    expect(mockClient.chat).toHaveBeenCalledWith({
+    expect(mockClient.chat).toHaveBeenCalledWith(expect.objectContaining({
       messages: [{ role: 'user', content: 'Hi' }],
       system: 'You are helpful.',
-    });
+      signal: expect.any(AbortSignal),
+    }));
 
     const history = agent.getHistory();
     expect(history).toHaveLength(2);