fix: cite legal basis in chat answers

backend/app/api/chat.py

@@ -371,11 +371,17 @@ def _merge_local_sources_into_stream(upstream: Iterable[str], local_sources: Lis
         return
 
     emitted_sources = False
+    emitted_basis_intro = False
+    basis_intro = _build_legal_basis_intro(local_sources)
     for chunk in upstream:
         event = _parse_sse_event(chunk)
         if event and event.get("type") == "text":
             content = str(event.get("content") or "")
-            yield _format_sse_event({"type": "text", "content": _polish_chat_answer(content, message, local_sources)})
+            polished_content = _polish_chat_answer(content, message, local_sources)
+            if basis_intro and not emitted_basis_intro:
+                emitted_basis_intro = True
+                polished_content = _prepend_legal_basis_intro(polished_content, basis_intro)
+            yield _format_sse_event({"type": "text", "content": polished_content})
             continue
         if event and event.get("type") == "sources":
             merged = _dedupe_sources([*(event.get("sources") or []), *local_sources])
@@ -388,6 +394,59 @@ def _merge_local_sources_into_stream(upstream: Iterable[str], local_sources: Lis
         yield chunk
 
 
+def _prepend_legal_basis_intro(content: str, basis_intro: str) -> str:
+    normalized_content = str(content or "").lstrip()
+    if not normalized_content:
+        return basis_intro
+    return f"{basis_intro}\n\n{normalized_content}"
+
+
+def _build_legal_basis_intro(sources: List[Dict[str, Any]]) -> str:
+    legal_sources = [source for source in sources if _is_legal_article_source(source)]
+    if not legal_sources:
+        return ""
+    lines = [
+        "本次回答已先检索本地法规库，优先依据如下法条：",
+    ]
+    for index, source in enumerate(legal_sources[:3], start=1):
+        citation = _format_legal_article_citation(source)
+        excerpt = _format_legal_article_excerpt(source.get("content"))
+        if excerpt:
+            lines.append(f"{index}. {citation}：{excerpt}")
+        else:
+            lines.append(f"{index}. {citation}")
+    lines.append("以下为结合上述依据形成的分析意见：")
+    return "\n".join(lines)
+
+
+def _is_legal_article_source(source: Mapping[str, Any]) -> bool:
+    detail_path = str(source.get("detail_path") or "")
+    return source.get("source_type") == "legal_article" or detail_path.startswith("/legal-articles")
+
+
+def _format_legal_article_citation(source: Mapping[str, Any]) -> str:
+    metadata = source.get("metadata") if isinstance(source.get("metadata"), Mapping) else {}
+    article_no = str(source.get("article_no") or "").strip()
+    source_title = str(metadata.get("source_title") or "").strip()
+    title = str(source.get("title") or "").strip()
+    if not source_title and article_no and title.endswith(article_no):
+        source_title = title[: -len(article_no)].strip()
+    if not source_title:
+        source_title = title
+    if source_title and article_no:
+        return f"《{source_title}》{article_no}"
+    return title or "本地法规库"
+
+
+def _format_legal_article_excerpt(value: Any, max_length: int = 120) -> str:
+    text = " ".join(str(value or "").split())
+    if not text:
+        return ""
+    if len(text) <= max_length:
+        return text
+    return f"{text[:max_length].rstrip()}..."
+
+
 def _polish_chat_answer(content: str, message: str, sources: List[Dict[str, Any]]) -> str:
     if not _looks_like_raw_retrieval_answer(content):
         return content

backend/tests/test_chat_api.py

@@ -325,9 +325,13 @@ class ChatApiTestCase(unittest.TestCase):
         self.assertEqual(response.status_code, 200)
         events = [line.removeprefix("data: ") for line in response.text.split("\n\n") if line.startswith("data: ")]
         payloads = [json.loads(item) for item in events]
+        text_event = next(item for item in payloads if item["type"] == "text")
         sources_event = next(item for item in payloads if item["type"] == "sources")
         legal_source = next(item for item in sources_event["sources"] if item.get("source_type") == "legal_article")
 
+        self.assertIn("本次回答已先检索本地法规库", text_event["content"])
+        self.assertIn("优先依据如下法条", text_event["content"])
+        self.assertIn("以下为结合上述依据形成的分析意见", text_event["content"])
         self.assertEqual(legal_source["source_id"], "lart-civil-585")
         self.assertEqual(legal_source["detail_path"], "/legal-articles?article_id=lart-civil-585")
         self.assertEqual(self.chat_service.stream_calls[0][3]["legalArticleRefs"][0]["id"], "lart-civil-585")
@@ -361,9 +365,13 @@ class ChatApiTestCase(unittest.TestCase):
         self.assertEqual(response.status_code, 200)
         events = [line.removeprefix("data: ") for line in response.text.split("\n\n") if line.startswith("data: ")]
         payloads = [json.loads(item) for item in events]
+        text_event = next(item for item in payloads if item["type"] == "text")
         sources_event = next(item for item in payloads if item["type"] == "sources")
         legal_source = next(item for item in sources_event["sources"] if item.get("source_type") == "legal_article")
 
+        self.assertIn("本次回答已先检索本地法规库", text_event["content"])
+        self.assertIn("优先依据如下法条", text_event["content"])
+        self.assertIn("以下为结合上述依据形成的分析意见", text_event["content"])
         self.assertEqual(legal_source["source_id"], "lart-cyber-001")
         self.assertEqual(legal_source["detail_path"], "/legal-articles?article_id=lart-cyber-001")
         self.assertEqual(legal_article_service.calls[0][1], "网络安全法第一条是什么")