feat(teacher-bff): admin 命名空间 + 5 个 gRPC client + health probes + merge-resolvers + nextstep 文档

services/teacher-bff/src/teacher/ai-chat-sse.controller.ts

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+// SSE 端点（P5：ai.StreamChat gRPC stream → BFF → 前端 EventSource）
+// 路由：GET /ai/chat/stream
+// 裁决依据：02-architecture-design.md §10
+import { Controller, Get, Query, Res, Req } from "@nestjs/common";
+import type { Request, Response } from "express";
+import { TeacherService } from "./teacher.service.js";
+import type { CallContext } from "../clients/types.js";
+import type { ChatMessage } from "../clients/ai/ai.types.js";
+
+@Controller("/ai/chat")
+export class AiChatSseController {
+  constructor(private readonly teacherService: TeacherService) {}
+
+  /**
+   * SSE 流式聊天端点
+   * 前端使用 EventSource 连接，BFF 透传 ai.StreamChat gRPC stream
+   */
+  @Get("stream")
+  async streamChat(
+    @Req() req: Request,
+    @Res() res: Response,
+    @Query("prompt") prompt: string,
+  ): Promise<void> {
+    // 设置 SSE 响应头
+    res.setHeader("Content-Type", "text/event-stream");
+    res.setHeader("Cache-Control", "no-cache");
+    res.setHeader("Connection", "keep-alive");
+    res.setHeader("X-Accel-Buffering", "no"); // 禁用 Nginx 缓冲
+
+    // 构造 CallContext（从 req.headers 提取 x-user-id 和 x-request-id）
+    const ctx: CallContext = {
+      userId: (req.headers["x-user-id"] as string) ?? "dev-user",
+      traceId: (req.headers["x-request-id"] as string) ?? "",
+    };
+
+    // 构造聊天消息
+    const messages: ChatMessage[] = [{ role: "user", content: prompt }];
+
+    try {
+      const stream = await this.teacherService.streamChat(ctx, messages);
+
+      for await (const chunk of stream) {
+        const data = JSON.stringify({
+          content: chunk.content,
+          done: chunk.done,
+        });
+        res.write(`data: ${data}\n\n`);
+
+        if (chunk.done) {
+          break;
+        }
+      }
+
+      res.write("event: done\ndata: {}\n\n");
+    } catch (err) {
+      const errorData = JSON.stringify({
+        error: err instanceof Error ? err.message : "Unknown error",
+      });
+      res.write(`event: error\ndata: ${errorData}\n\n`);
+    } finally {
+      res.end();
+    }
+  }
+}