fix(agent): serialize retrieval trace responses

ai_knowledge_base_v2/apps/backend/app/core/exception_handlers.py

@@ -16,6 +16,10 @@ def register_exception_handlers(app: FastAPI) -> None:
     async def validation_exception_handler(request: Request, exc: RequestValidationError) -> JSONResponse:
         return JSONResponse(status_code=422, content=api_error(10000, "请求参数不正确", exc.errors()))
 
+    @app.exception_handler(Exception)
+    async def unhandled_exception_handler(request: Request, exc: Exception) -> JSONResponse:
+        return JSONResponse(status_code=500, content=api_error(50000, "系统内部错误，请稍后重试"))
+
 
 def _code_from_status(status_code: int) -> int:
     if status_code in {401, 403}:

ai_knowledge_base_v2/apps/backend/app/services/knowledge_agent_service.py

@@ -127,7 +127,7 @@ class KnowledgeAgentService:
                 log.selected_knowledge_ids = ",".join(str(item) for item in selected_ids)
                 log.query_terms = json.dumps(terms, ensure_ascii=False)
                 log.final_section_ids = ",".join(str(item.section.id) for item in selected)
-            log.tool_trace = json.dumps(trace, ensure_ascii=False)
+            log.tool_trace = _dump_trace(trace)
             log.tool_cost_ms = int((perf_counter() - started) * 1000)
             log.status = "prepared"
             db.add(log)
@@ -152,7 +152,7 @@ class KnowledgeAgentService:
         except Exception as exc:
             log.status = "failed"
             log.error_message = str(exc)
-            log.tool_trace = json.dumps(trace, ensure_ascii=False)
+            log.tool_trace = _dump_trace(trace)
             log.tool_cost_ms = int((perf_counter() - started) * 1000)
             db.add(log)
             raise
@@ -431,6 +431,18 @@ class KnowledgeAgentService:
         return content if len(content) <= 3200 else content[:3200].rstrip() + "\n[章节内容已按保护规则截断]"
 
 
+def _dump_trace(trace: list[dict]) -> str:
+    """Persist tool traces without failing on database datetime values."""
+    return json.dumps(trace, ensure_ascii=False, default=_json_trace_value)
+
+
+def _json_trace_value(value):
+    isoformat = getattr(value, "isoformat", None)
+    if callable(isoformat):
+        return isoformat()
+    return str(value)
+
+
 def _extract_json(value: str) -> str:
     match = re.search(r"\{[\s\S]*\}", value)
     if not match: