feat(openai): cyber_policy 硬阻断全链路透传、审计与计费

上游对单次请求下发 error.code=cyber_policy 硬阻断时,网关在所有端点
(/v1/responses、/v1/chat/completions、/v1/messages、WebSocket)及流式/
非流式路径下,将该结果原样透传给客户端,绝不 failover、换号或同步拦截;
命中后异步完成审计与计费:

- 风控中心记录 cyber_policy 留痕并发送通知邮件,落库先于发信,SMTP 阻塞
  不影响留痕
- ops 错误请求记录,状态码对齐客户端实际接收(流式 200 / 非流式 400)
- 用量明细标记 request_type=cyber,按上游真实 token 计费,HTTP 与
  WebSocket 计费口径统一,零 token 命中不误扣
- 会话级自动屏蔽(管理员开关,默认关):命中的会话在可配 TTL 内本地拦截
  不再发往上游,仅屏蔽该会话不影响同 Key 其他会话
- 封号计数排除开关:可选让 cyber 命中不计入自动封号,命中当次不判定且
  历史行在违规计数中一并排除

WebSocket 多轮连接下 cyber 标记按 turn 生命周期管理,逐轮独立检测与记录;
透传的错误响应不被兜底逻辑追加内容污染。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/internal/handler/openai_gateway_handler_test.go

@@ -805,7 +805,7 @@ func (r *contentModerationHandlerTestRepo) ListLogs(ctx context.Context, filter
 	return nil, nil, nil
 }
 
-func (r *contentModerationHandlerTestRepo) CountFlaggedByUserSince(ctx context.Context, userID int64, since time.Time) (int, error) {
+func (r *contentModerationHandlerTestRepo) CountFlaggedByUserSince(ctx context.Context, userID int64, since time.Time, excludeCyberPolicy bool) (int, error) {
 	return 0, nil
 }
 
@@ -813,6 +813,10 @@ func (r *contentModerationHandlerTestRepo) CleanupExpiredLogs(ctx context.Contex
 	return &service.ContentModerationCleanupResult{}, nil
 }
 
+func (r *contentModerationHandlerTestRepo) UpdateLogEmailSent(ctx context.Context, id int64, sent bool) error {
+	return nil
+}
+
 func TestOpenAIResponsesWebSocket_ContentModerationBlocksFirstFrame(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 
@@ -1654,4 +1658,28 @@ data: {"type":"response.failed","error":{"message":"This content was flagged"}}
 
 		require.False(t, reported)
 	})
+
+	// H-2: cyber_policy 命中且响应已写出时，即便 err 前缀不在白名单（非流式 400 cyber
+	// 返回 "openai cyber_policy:"、透传账号返回 "upstream error:"），也须判定已透传，避免
+	// ensureForwardErrorResponse 在已写出的完整响应尾部追加 SSE 污染响应体。
+	t.Run("cyber policy hit after write is already communicated", func(t *testing.T) {
+		w := httptest.NewRecorder()
+		c, _ := gin.CreateTestContext(w)
+		c.Request = httptest.NewRequest(http.MethodPost, EndpointResponses, nil)
+		service.MarkOpsCyberPolicy(c, service.CyberPolicyMark{Message: "blocked", UpstreamStatus: 400})
+		before := c.Writer.Size()
+		_, _ = c.Writer.WriteString(`{"error":{"code":"cyber_policy","message":"blocked"}}`)
+
+		require.True(t, openAIForwardErrorAlreadyCommunicated(c, before, errors.New("openai cyber_policy: blocked")))
+	})
+
+	// Size 守卫优先于 cyber 短路：cyber 命中但未写出任何响应时仍需补写错误。
+	t.Run("cyber policy without write still needs fallback", func(t *testing.T) {
+		w := httptest.NewRecorder()
+		c, _ := gin.CreateTestContext(w)
+		c.Request = httptest.NewRequest(http.MethodPost, EndpointResponses, nil)
+		service.MarkOpsCyberPolicy(c, service.CyberPolicyMark{Message: "blocked", UpstreamStatus: 400})
+
+		require.False(t, openAIForwardErrorAlreadyCommunicated(c, c.Writer.Size(), errors.New("openai cyber_policy: blocked")))
+	})
 }