feat(open-chat): 开放问答接口回传生成文件 + 临时不留存

- /api/open/chat[/stream] 新增 include_files(默认开)，把智能体在 outputs 目录
  生成的文件(name/virtual_path/encoding(text|base64)/content)随结果回传，
  解决"报告写进文件、answer 只回一段总结"导致拿不到完整内容的问题；
  既无 answer 也无文件时返回 502。
- 无状态运行标记 ephemeral：lead agent 跳过记忆与知识库中间件(不召回/不留存/
  不自动沉淀)，取完文件后清理临时线程目录，做到"通过本接口的聊天记录不存储"。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

offline-backend-20260512/backend/packages/harness/deerflow/agents/lead_agent/agent.py

@@ -306,17 +306,25 @@ def _build_middlewares(
     if not cfg.get("is_scheduled_run", False):
         middlewares.append(TitleMiddleware(app_config=resolved_app_config))
 
-    # Add MemoryMiddleware (after TitleMiddleware) — skip in bootstrap mode (agent creation flow)
+    # Ephemeral runs (e.g. the open Q&A API /api/open/chat) must NOT touch any
+    # server-side per-user state: no memory recall/retain, no knowledge-base
+    # recall/auto-ingest. Those runs use the shared "default" user bucket, so
+    # persisting their conversations there would both store records the caller
+    # explicitly asked NOT to keep and leak content across unrelated callers.
+    # Skip both write-capable middlewares entirely.
+    is_ephemeral = cfg.get("ephemeral", False)
+
+    # Add MemoryMiddleware (after TitleMiddleware) — skip in bootstrap mode (agent creation flow) and ephemeral runs
     memory_injection_enabled = cfg.get("memory_injection_enabled", True)
-    if not is_bootstrap and not is_writing_setup:
+    if not is_bootstrap and not is_writing_setup and not is_ephemeral:
         middlewares.append(MemoryMiddleware(agent_name=agent_name, memory_config=resolved_app_config.memory, injection_enabled=memory_injection_enabled))
 
     # KnowledgeRagMiddleware — inject knowledge-base recall (phase 2). Gated
     # per-conversation by the ``knowledge_rag_enabled`` runtime flag, defaulting
     # to the global ``knowledge.rag_enabled`` config. No-op when knowledge is
-    # disabled. Skipped in bootstrap/writing-setup like MemoryMiddleware.
+    # disabled. Skipped in bootstrap/writing-setup/ephemeral like MemoryMiddleware.
     knowledge_cfg = getattr(resolved_app_config, "knowledge", None)
-    if not is_bootstrap and not is_writing_setup and knowledge_cfg is not None and knowledge_cfg.enabled:
+    if not is_bootstrap and not is_writing_setup and not is_ephemeral and knowledge_cfg is not None and knowledge_cfg.enabled:
         from deerflow.agents.middlewares.knowledge_rag_middleware import KnowledgeRagMiddleware
 
         middlewares.append(KnowledgeRagMiddleware(limit=knowledge_cfg.rag_limit, default_enabled=knowledge_cfg.rag_enabled))