fix(assistant): 上游返回空串 reasoning_content 时也保留该字段

按字段存在性 (is not None) 判断, 区分"上游未返回"与"返回空串";
流式 round_end、chat_service 下一轮请求、非流式工具循环三处均补齐, 并加回归用例。

Signed-off-by: kevin9327 <5299031+kevin9327@users.noreply.github.com>

backend/app/custom/assistant/chat_service.py

@@ -268,14 +268,14 @@ async def chat_stream(
             while True:
                 round_text: list[str] = []
                 tool_calls: list[dict[str, Any]] = []
-                reasoning_content = ""
+                reasoning_content: str | None = None
                 async for event in stream_round(req_messages, schemas, temperature=0.3, timeout=240.0):
                     if event["type"] == "text":
                         round_text.append(event["delta"])
                         await queue.put({"type": "delta", "content": event["delta"]})
                     elif event["type"] == "round_end":
                         tool_calls = event.get("tool_calls") or []
-                        reasoning_content = event.get("reasoning_content") or ""
+                        reasoning_content = event.get("reasoning_content")
 
                 if not tool_calls:
                     if not round_text and not text_seen:
@@ -322,7 +322,7 @@ async def chat_stream(
                     assistant_message["content"] = "".join(round_text)
                     text_seen = True
                 # DeepSeek 思考模式要求工具轮的 reasoning_content 原样回传, 否则下一轮 400。
-                if reasoning_content:
+                if reasoning_content is not None:
                     assistant_message["reasoning_content"] = reasoning_content
                 req_messages.append(assistant_message)
 

backend/app/custom/assistant/streaming.py

@@ -125,6 +125,8 @@ async def stream_openai_round(
     content_seen = False
     reasoning_seen = False
     reasoning_parts: list[str] = []
+    # 上游显式返回 reasoning_content (哪怕是空串) 时也要在 round_end 里回传该字段。
+    reasoning_field_seen = False
     finish_reason = ""
     calls: dict[int, dict[str, Any]] = {}
     ordered: list[dict[str, Any]] = []
@@ -141,6 +143,8 @@ async def stream_openai_round(
         if delta is None:
             continue
         reasoning = getattr(delta, "reasoning_content", None)
+        if reasoning is not None:
+            reasoning_field_seen = True
         if reasoning:
             reasoning_seen = True
             reasoning_parts.append(str(reasoning))
@@ -191,7 +195,7 @@ async def stream_openai_round(
             "finish_reason": finish_reason,
         }
         # DeepSeek 思考模式: 带 tools 的后续请求缺了这一轮的 reasoning_content 会被 400。
-        if reasoning_parts:
+        if reasoning_field_seen:
             end["reasoning_content"] = "".join(reasoning_parts)
         yield end
         return

backend/app/services/ai_provider.py

@@ -426,7 +426,7 @@ async def generate_ai_text_with_tools(
             assistant["content"] = message.content
         # DeepSeek 思考模式要求工具轮的 reasoning_content 原样回传, 否则下一轮 400。
         reasoning = getattr(message, "reasoning_content", None)
-        if reasoning:
+        if reasoning is not None:
             assistant["reasoning_content"] = reasoning
         req_messages.append(assistant)
 

backend/tests/test_assistant_reasoning_content.py

@@ -83,11 +83,24 @@ async def test_stream_round_end_without_reasoning_has_no_key(monkeypatch: pytest
     assert "reasoning_content" not in events[-1]
 
 
-async def test_chat_service_sends_reasoning_content_back(monkeypatch: pytest.MonkeyPatch) -> None:
+async def test_stream_round_end_keeps_empty_reasoning_content(monkeypatch: pytest.MonkeyPatch) -> None:
+    # 上游显式返回空串时也要保留字段, 与"未返回该字段"区分开。
+    events = await _events(monkeypatch, [
+        _chunk({"reasoning_content": ""}),
+        _chunk({"tool_calls": [{"index": 0, "id": "call_1", "type": "function",
+                                "function": {"name": "list_strategies", "arguments": "{}"}}]},
+               finish_reason="tool_calls"),
+    ])
+
+    assert events[-1]["reasoning_content"] == ""
+
+
+@pytest.mark.parametrize("reasoning", ["先看看有哪些策略", ""])
+async def test_chat_service_sends_reasoning_content_back(monkeypatch: pytest.MonkeyPatch, reasoning: str) -> None:
     captured: list[list[dict[str, Any]]] = []
     script = [
         {"tool_calls": [{"id": "call_1", "name": "list_strategies", "arguments": "{}"}],
-         "reasoning_content": "先看看有哪些策略"},
+         "reasoning_content": reasoning},
         {"text": "你有 3 个策略"},
     ]
 
@@ -97,7 +110,7 @@ async def test_chat_service_sends_reasoning_content_back(monkeypatch: pytest.Mon
         if step.get("text"):
             yield {"type": "text", "delta": step["text"]}
         end = {"type": "round_end", "tool_calls": step.get("tool_calls", []), "finish_reason": "stop"}
-        if step.get("reasoning_content"):
+        if "reasoning_content" in step:
             end["reasoning_content"] = step["reasoning_content"]
         yield end
 
@@ -115,15 +128,16 @@ async def test_chat_service_sends_reasoning_content_back(monkeypatch: pytest.Mon
     assert [json.loads(line) for line in lines if '"error"' in line] == []
     assistant_msg = captured[1][-2]
     assert assistant_msg["role"] == "assistant"
-    assert assistant_msg["reasoning_content"] == "先看看有哪些策略"
+    assert assistant_msg["reasoning_content"] == reasoning
 
 
-async def test_tool_loop_sends_reasoning_content_back(monkeypatch: pytest.MonkeyPatch) -> None:
+@pytest.mark.parametrize("reasoning", ["先跑一次回测", ""])
+async def test_tool_loop_sends_reasoning_content_back(monkeypatch: pytest.MonkeyPatch, reasoning: str) -> None:
     replies = [
         ChatCompletionMessage.model_validate({
             "role": "assistant",
             "content": None,
-            "reasoning_content": "先跑一次回测",
+            "reasoning_content": reasoning,
             "tool_calls": [{"id": "call_1", "type": "function",
                             "function": {"name": "run_backtest", "arguments": "{}"}}],
         }),
@@ -147,5 +161,5 @@ async def test_tool_loop_sends_reasoning_content_back(monkeypatch: pytest.Monkey
         execute_tool=fake_execute,
     )
 
-    assert messages[1]["reasoning_content"] == "先跑一次回测"
+    assert messages[1]["reasoning_content"] == reasoning
     assert "reasoning_content" not in messages[3]