Add server tool timeout protection

engine/tests/test_tool_call_flow.py

@@ -252,3 +252,50 @@ async def test_server_calculator_emits_tool_result(monkeypatch):
     payload = tool_results[-1].get("result", {})
     assert payload.get("status", {}).get("code") == 200
     assert payload.get("output", {}).get("result") == 3
+
+
+@pytest.mark.asyncio
+async def test_server_tool_timeout_emits_504_and_continues(monkeypatch):
+    async def _slow_execute(_call):
+        await asyncio.sleep(0.05)
+        return {
+            "tool_call_id": "call_slow",
+            "name": "weather",
+            "output": {"ok": True},
+            "status": {"code": 200, "message": "ok"},
+        }
+
+    monkeypatch.setattr("core.duplex_pipeline.execute_server_tool", _slow_execute)
+
+    pipeline, events = _build_pipeline(
+        monkeypatch,
+        [
+            [
+                LLMStreamEvent(
+                    type="tool_call",
+                    tool_call={
+                        "id": "call_slow",
+                        "executor": "server",
+                        "type": "function",
+                        "function": {"name": "weather", "arguments": "{\"city\":\"hz\"}"},
+                    },
+                ),
+                LLMStreamEvent(type="done"),
+            ],
+            [
+                LLMStreamEvent(type="text_delta", text="timeout fallback."),
+                LLMStreamEvent(type="done"),
+            ],
+        ],
+    )
+    pipeline._SERVER_TOOL_TIMEOUT_SECONDS = 0.01
+
+    await pipeline._handle_turn("weather?")
+
+    tool_results = [e for e in events if e.get("type") == "assistant.tool_result"]
+    assert tool_results
+    payload = tool_results[-1].get("result", {})
+    assert payload.get("status", {}).get("code") == 504
+    finals = [e for e in events if e.get("type") == "assistant.response.final"]
+    assert finals
+    assert "timeout fallback" in finals[-1].get("text", "")