fix: harden tenant auth and quality gates

api/src/auth/current-tenant-id.decorator.ts

@@ -0,0 +1,14 @@
+import { ForbiddenException, createParamDecorator, ExecutionContext } from '@nestjs/common';
+import type { SessionRequest } from './session-validation.middleware';
+
+/**
+ * Returns the tenant bound to the authenticated client session.
+ * Request headers, query parameters and request bodies must never determine this value.
+ */
+export const CurrentTenantId = createParamDecorator((_: unknown, context: ExecutionContext) => {
+  const request = context.switchToHttp().getRequest<SessionRequest>();
+  if (request.authSession?.portal !== 'client' || !request.sessionTenantId) {
+    throw new ForbiddenException({ code: 'CLIENT_TENANT_REQUIRED', message: '缺少可信企业上下文' });
+  }
+  return request.sessionTenantId;
+});