fix(coding-runtime): close Pi extension lifecycle races

tests/unit/pi-interaction.test.ts

@@ -75,4 +75,43 @@ describe('Pi interaction store', () => {
     expect(changes.map(({ status }) => status)).toEqual(['cancelled', 'cancelled']);
     expect(store.list()).toEqual([]);
   });
+
+  it('makes response ownership atomic across double submit and generation invalidation', async () => {
+    const sent: PiRpcCommand[] = [];
+    const changes: ConversationInteraction[] = [];
+    let cancelResource = () => undefined;
+    let releaseSend = () => undefined;
+    const sendGate = new Promise<void>((resolve) => { releaseSend = resolve; });
+    const store = new PiInteractionStore({
+      getState: () => ({
+        conversationId: 'conversation-a', workerId: 'worker-a', state: 'running', generation: 1,
+        session: { piSessionId: 'session-a', sessionKey: 'key-a' },
+      }),
+      getActiveRun: () => ({ generation: 1, runId: 'run-1' }),
+      send: async (_conversationId, command) => {
+        sent.push(command);
+        await sendGate;
+      },
+      trackGenerationResource: (input) => {
+        cancelResource = input.cancel;
+        return () => undefined;
+      },
+    }, (interaction) => changes.push(interaction));
+    store.open('conversation-a', 1, 'run-1', {
+      type: 'extension_ui_request', id: 'question-race', method: 'confirm', title: 'Continue?',
+    });
+
+    const first = store.respond('conversation-a', {
+      interactionId: 'question-race', confirmed: true,
+    });
+    await expect(store.respond('conversation-a', {
+      interactionId: 'question-race', confirmed: false,
+    })).rejects.toThrow('already in progress');
+    cancelResource();
+    releaseSend();
+
+    await expect(first).rejects.toThrow('stale');
+    expect(sent).toHaveLength(1);
+    expect(changes.map(({ status }) => status)).toEqual(['cancelled']);
+  });
 });