fix: search_hybrid 改用改写后的 retrieval_query + 清理 engine.py 死代码

关键修复:
- chat_routes.py: search_hybrid(message,...) → search_hybrid(retrieval_query,...)
  修复无状态模式下追问场景("那工作流程呢？")用原始模糊文本做向量检索的问题，
  现在使用意图分析改写后的完整查询("货源投放的具体工作流程是什么？")

死代码清理 (Claude Code review 反馈):
- engine.py: 移除 4 处未使用的 doc_ids 变量和 2 处过时注释

api/chat_routes.py

@@ -2351,7 +2351,7 @@ def rag():
                 sub_queries = intent.sub_queries
 
             search_result = search_hybrid(
-                message,
+                retrieval_query,
                 top_k=RAG_SEARCH_TOP_K,
                 candidates=RAG_SEARCH_CANDIDATES,
                 allowed_collections=collections,

core/engine.py

@@ -559,7 +559,6 @@ class RAGEngine:
                 top_dist = result['distances'][0][0] if result.get('distances') and result['distances'][0] else 1.0
                 top_score = 1.0 - top_dist
                 if top_score >= CACHE_MIN_SCORE:
-                    doc_ids = result.get('ids', [[]])[0] if result.get('ids') else []
                     cache.set_query_result(query, kb_name, result)
             result['_debug'] = _debug
             return result
@@ -581,7 +580,6 @@ class RAGEngine:
                         top_dist = result['distances'][0][0] if result.get('distances') and result['distances'][0] else 1.0
                         top_score = 1.0 - top_dist
                         if top_score >= CACHE_MIN_SCORE:
-                            doc_ids = result.get('ids', [[]])[0] if result.get('ids') else []
                             cache.set_query_result(query, kb_name, result)
                     result['_debug'] = _debug
                     return result
@@ -617,8 +615,6 @@ class RAGEngine:
                 top_dist = result['distances'][0][0] if result.get('distances') and result['distances'][0] else 1.0
                 top_score = 1.0 - top_dist
                 if top_score >= CACHE_MIN_SCORE:
-                    # 传递 doc_ids 实现细粒度缓存失效
-                    doc_ids = result.get('ids', [[]])[0] if result.get('ids') else []
                     cache.set_query_result(query, kb_name, result)
             _debug['timing']['total_ms'] = int((time.time() - _overall_start) * 1000)
             result['_debug'] = _debug
@@ -810,8 +806,6 @@ class RAGEngine:
             top_dist = fused_results['distances'][0][0] if fused_results.get('distances') and fused_results['distances'][0] else 1.0
             top_score = 1.0 - top_dist  # 距离转相似度
             if top_score >= CACHE_MIN_SCORE:  # 置信度阈值
-                # 传递 doc_ids 实现细粒度缓存失效
-                doc_ids = fused_results.get('ids', [[]])[0] if fused_results.get('ids') else []
                 cache.set_query_result(query, kb_name, fused_results)
 
         fused_results['_debug'] = _debug