refactor: extract shared agent runner and preserve subagent progress on failure

tests/agent/test_task_cancel.py

@@ -221,3 +221,83 @@ class TestSubagentCancellation:
         assert len(assistant_messages) == 1
         assert assistant_messages[0]["reasoning_content"] == "hidden reasoning"
         assert assistant_messages[0]["thinking_blocks"] == [{"type": "thinking", "thinking": "step"}]
+
+    @pytest.mark.asyncio
+    async def test_subagent_announces_error_when_tool_execution_fails(self, monkeypatch, tmp_path):
+        from nanobot.agent.subagent import SubagentManager
+        from nanobot.bus.queue import MessageBus
+        from nanobot.providers.base import LLMResponse, ToolCallRequest
+
+        bus = MessageBus()
+        provider = MagicMock()
+        provider.get_default_model.return_value = "test-model"
+        provider.chat_with_retry = AsyncMock(return_value=LLMResponse(
+            content="thinking",
+            tool_calls=[ToolCallRequest(id="call_1", name="list_dir", arguments={})],
+        ))
+        mgr = SubagentManager(provider=provider, workspace=tmp_path, bus=bus)
+        mgr._announce_result = AsyncMock()
+
+        calls = {"n": 0}
+
+        async def fake_execute(self, name, arguments):
+            calls["n"] += 1
+            if calls["n"] == 1:
+                return "first result"
+            raise RuntimeError("boom")
+
+        monkeypatch.setattr("nanobot.agent.tools.registry.ToolRegistry.execute", fake_execute)
+
+        await mgr._run_subagent("sub-1", "do task", "label", {"channel": "test", "chat_id": "c1"})
+
+        mgr._announce_result.assert_awaited_once()
+        args = mgr._announce_result.await_args.args
+        assert "Completed steps:" in args[3]
+        assert "- list_dir: first result" in args[3]
+        assert "Failure:" in args[3]
+        assert "- list_dir: boom" in args[3]
+        assert args[5] == "error"
+
+    @pytest.mark.asyncio
+    async def test_cancel_by_session_cancels_running_subagent_tool(self, monkeypatch, tmp_path):
+        from nanobot.agent.subagent import SubagentManager
+        from nanobot.bus.queue import MessageBus
+        from nanobot.providers.base import LLMResponse, ToolCallRequest
+
+        bus = MessageBus()
+        provider = MagicMock()
+        provider.get_default_model.return_value = "test-model"
+        provider.chat_with_retry = AsyncMock(return_value=LLMResponse(
+            content="thinking",
+            tool_calls=[ToolCallRequest(id="call_1", name="list_dir", arguments={})],
+        ))
+        mgr = SubagentManager(provider=provider, workspace=tmp_path, bus=bus)
+        mgr._announce_result = AsyncMock()
+
+        started = asyncio.Event()
+        cancelled = asyncio.Event()
+
+        async def fake_execute(self, name, arguments):
+            started.set()
+            try:
+                await asyncio.sleep(60)
+            except asyncio.CancelledError:
+                cancelled.set()
+                raise
+
+        monkeypatch.setattr("nanobot.agent.tools.registry.ToolRegistry.execute", fake_execute)
+
+        task = asyncio.create_task(
+            mgr._run_subagent("sub-1", "do task", "label", {"channel": "test", "chat_id": "c1"})
+        )
+        mgr._running_tasks["sub-1"] = task
+        mgr._session_tasks["test:c1"] = {"sub-1"}
+
+        await started.wait()
+
+        count = await mgr.cancel_by_session("test:c1")
+
+        assert count == 1
+        assert cancelled.is_set()
+        assert task.cancelled()
+        mgr._announce_result.assert_not_awaited()