feat(knowledge): 阶段二 向量 RAG 与召回注入

- embeddings.py：OpenAI 兼容 embedding 客户端，未配置时关键词兜底
- chunking.py + knowledge_embeddings 表：Markdown 分块与向量索引（Python 余弦）
- search.py：keyword/vector/hybrid 三种模式，向量不可用自动降级
- 笔记创建/更新自动重建向量索引；新增 /reindex 维护接口
- KnowledgeRagMiddleware：按对话级开关 knowledge_rag_enabled 注入 <knowledge-context>，接入 lead agent 中间件链（默认随 config.knowledge.rag_enabled）
- service.build_rag_context（wiki-query 风格分层召回）
- 笔记版本快照（knowledge_note_versions）+ GET /notes/{id}/versions
- 前端：聊天页「知识库」对话级 RAG 开关 + 类型字段
- 新增 entities/relations 表（阶段四预置）

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

frontend-web/src/components/workspace/knowledge-rag-toggle.tsx

@@ -0,0 +1,44 @@
+"use client";
+
+import { Database } from "lucide-react";
+
+import { Button } from "@/components/ui/button";
+import { useThreadSettings } from "@/core/settings";
+import { cn } from "@/lib/utils";
+
+import { Tooltip } from "./tooltip";
+
+/**
+ * Per-conversation toggle for knowledge-base RAG injection (phase 2).
+ *
+ * Writes ``context.knowledge_rag_enabled`` into the thread settings, which the
+ * run forwards as ``runtime.context`` so ``KnowledgeRagMiddleware`` injects
+ * recalled knowledge before each model call for this conversation only.
+ */
+export function KnowledgeRagToggle({ threadId }: { threadId: string }) {
+  const [settings, setSettings] = useThreadSettings(threadId);
+  const enabled = settings.context.knowledge_rag_enabled === true;
+
+  const toggle = () => {
+    setSettings("context", {
+      ...settings.context,
+      knowledge_rag_enabled: !enabled,
+    });
+  };
+
+  return (
+    <Tooltip content={enabled ? "知识库召回：已开启" : "知识库召回：已关闭"}>
+      <Button
+        variant="ghost"
+        onClick={toggle}
+        className={cn(
+          "text-muted-foreground hover:text-foreground",
+          enabled && "text-primary hover:text-primary",
+        )}
+      >
+        <Database />
+        知识库
+      </Button>
+    </Tooltip>
+  );
+}

frontend-web/src/core/threads/types.ts

@@ -18,9 +18,11 @@ export interface AgentThreadContext extends Record<string, unknown> {
   reasoning_effort?: "minimal" | "low" | "medium" | "high";
   writing_mode?: boolean;
   writing_artifact_path?: string;
-  memory_injection_enabled?: boolean;
-  rag_mode_enabled?: boolean;
-  agent_id?: string;
+  memory_injection_enabled?: boolean;
+  rag_mode_enabled?: boolean;
+  /** Per-conversation switch for knowledge-base RAG injection (phase 2). */
+  knowledge_rag_enabled?: boolean;
+  agent_id?: string;
   /** @deprecated kept for reading legacy thread metadata; prefer agent_id */
   agent_name?: string;
 }

frontend-web/src/pages/ChatPage.tsx

@@ -16,6 +16,7 @@ import {
 } from "@/components/workspace/chats";
 import { ExportTrigger } from "@/components/workspace/export-trigger";
 import { KnowledgeSaveTrigger } from "@/components/workspace/knowledge-save-trigger";
+import { KnowledgeRagToggle } from "@/components/workspace/knowledge-rag-toggle";
 import { InputBox } from "@/components/workspace/input-box";
 import {
   MessageList,
@@ -409,6 +410,7 @@ export default function ChatPage() {
                 enabled={tokenUsageEnabled}
                 messages={thread.messages}
               />
+              <KnowledgeRagToggle threadId={threadId} />
               <ExportTrigger threadId={threadId} />
               <KnowledgeSaveTrigger threadId={threadId} />
               <ArtifactTrigger />