feat(teacher-bff): 完整实现 teacher-bff GraphQL 聚合层

包含 clients/graphql/middleware、health probes、shared-ts contracts 等

services/teacher-bff/src/graphql/context.ts

@@ -0,0 +1,37 @@
+// GraphQL 上下文构建（B1 裁决：P2 起直接 GraphQL）
+// 从 Express 请求提取 userId / traceId，注入下游 CallContext
+import type { Request } from "express";
+import type { CallContext } from "../clients/types.js";
+import { UnauthorizedError } from "../shared/errors/application-error.js";
+
+export interface GraphQLOperationContext {
+  /** 当前请求的 CallContext（注入下游 gRPC 调用） */
+  callCtx: CallContext;
+}
+
+/**
+ * 从 Express 请求构建 GraphQL 上下文
+ * P2: 从 x-user-id header 提取 userId（api-gateway 注入）
+ * P3+: 从 JWT 提取（api-gateway 校验后注入 x-user-id + x-user-roles）
+ */
+export function buildGraphQLContext(req: Request): GraphQLOperationContext {
+  const userIdHeader = req.headers["x-user-id"];
+  const userId = typeof userIdHeader === "string" ? userIdHeader : undefined;
+  if (!userId) {
+    throw new UnauthorizedError("Missing x-user-id header");
+  }
+
+  const requestIdHeader = req.headers["x-request-id"];
+  const traceId =
+    typeof requestIdHeader === "string" ? requestIdHeader : undefined;
+
+  const rolesHeader = req.headers["x-user-roles"];
+  const roles =
+    typeof rolesHeader === "string"
+      ? rolesHeader.split(",").filter(Boolean)
+      : undefined;
+
+  return {
+    callCtx: { userId, traceId, roles },
+  };
+}