feat: #70 ChatSession 新增 knowledgeItemIds 字段，限定 AI 检索范围

- Prisma schema: ChatSession 加 knowledgeItemIds Json? 字段
- createSession: 接受可选 knowledgeItemIds 参数
- loadContext: 支持 itemIds 过滤，传入时只检索指定知识点
- sendMessage/sendMessageStream: 读取 session.knowledgeItemIds 传入 loadContext

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

prisma/schema.prisma

@@ -1001,6 +1001,7 @@ model ChatSession {
   userId          String
   knowledgeBaseId String
   title           String   @default("新对话") @db.VarChar(200)
+  knowledgeItemIds Json?    @default("[]")
   createdAt       DateTime @default(now())
   updatedAt       DateTime @updatedAt
 

src/modules/rag-chat/rag-chat.controller.ts

@@ -13,8 +13,8 @@ export class RagChatController {
 
   @Post('sessions')
   @ApiOperation({ summary: '创建对话' })
-  async createSession(@CurrentUser() user: UserPayload, @Body() dto: { knowledgeBaseId: string; title?: string }) {
+  async createSession(@CurrentUser() user: UserPayload, @Body() dto: { knowledgeBaseId: string; title?: string; knowledgeItemIds?: string[] }) {
-    return this.svc.createSession(String(user.id), dto.knowledgeBaseId, dto.title);
+    return this.svc.createSession(String(user.id), dto.knowledgeBaseId, dto.title, dto.knowledgeItemIds);
   }
 
   @Get('sessions')

src/modules/rag-chat/rag-chat.service.ts

@@ -17,9 +17,14 @@ export class RagChatService {
     @Optional() private readonly aiGateway?: AiGatewayService,
   ) {}
 
-  async createSession(userId: string, knowledgeBaseId: string, title?: string) {
+  async createSession(userId: string, knowledgeBaseId: string, title?: string, knowledgeItemIds?: string[]) {
     return this.prisma.chatSession.create({
-      data: { userId, knowledgeBaseId, title: title || '新对话' },
+      data: {
+        userId,
+        knowledgeBaseId,
+        title: title || '新对话',
+        knowledgeItemIds: knowledgeItemIds ?? [],
+      },
     });
   }
 
@@ -55,7 +60,8 @@ export class RagChatService {
 
     // Retrieve knowledge base context
     this.logger.log(`RAG: kbId=${session.knowledgeBaseId}, content preview: ${content.substring(0, 30)}`);
-    const context = await this.loadContext(session.knowledgeBaseId);
+    const itemIds = (session as any).knowledgeItemIds as string[] | undefined;
+    const context = await this.loadContext(session.knowledgeBaseId, itemIds?.length ? itemIds : undefined);
     this.logger.log(`RAG context: isEmpty=${context.isEmpty}, textLen=${context.text.length}, citations=${context.citations.length}, aiGateway=${!!this.aiGateway}`);
 
     // Generate AI response
@@ -141,7 +147,8 @@ export class RagChatService {
     // Also auto-title in sendMessage (this is the sync method)
 
     // Load context
-    const context = await this.loadContext(session.knowledgeBaseId);
+    const itemIds = (session as any).knowledgeItemIds as string[] | undefined;
+    const context = await this.loadContext(session.knowledgeBaseId, itemIds?.length ? itemIds : undefined);
     if (!context.text) {
       yield { type: 'content', content: this.fallbackReply(true) };
     } else {
@@ -186,10 +193,14 @@ export class RagChatService {
 
   // ── Private ──
 
-  private async loadContext(kbId: string) {
+  private async loadContext(kbId: string, itemIds?: string[]) {
     try {
       const items = await this.prisma.knowledgeItem.findMany({
-        where: { knowledgeBaseId: kbId, deletedAt: null },
+        where: {
+          knowledgeBaseId: kbId,
+          deletedAt: null,
+          ...(itemIds && itemIds.length > 0 ? { id: { in: itemIds } } : {}),
+        },
         select: { id: true, title: true, content: true, summary: true },
         orderBy: { updatedAt: 'desc' },
         take: 30,