fix: reuse active security challenge before rate limit

docs/IM-前后端对接文档.md

@@ -761,8 +761,10 @@ X-MeetingIM-APIKey: <预置的普通 API Key>
 
 - 敏感操作先调用 `POST /v1/im/security/challenges`，Body `{"scene":"close_youth_mode","channel":"sms"}`；手机号由登录身份读取，客户端不提交目标手机号。
 - 发码/校验：服务端返回 `challenge_id` 和脱敏手机号；提交 `POST /v1/im/security/challenges/{id}/verify`，Body `{"code":"..."}`。
+- 重复发码：同一用户、同一手机号、同一敏感场景存在未过期 challenge 且仍在 `resend_after_seconds` 冷却期内时，服务端返回 HTTP `429 VERIFICATION_RATE_LIMITED`，`details` 带 `challenge_id` 和 `retry_after_seconds`。客户端应复用该 `challenge_id` 继续倒计时，不要当成接口不可达或重新登录。
+- 小时限流：超过一小时创建次数上限时同样返回 HTTP `429 VERIFICATION_RATE_LIMITED`，`details.retry_after_seconds` 可能大于 60 秒且不一定带 `challenge_id`。客户端只展示倒计时，倒计时结束后允许用户重新获取验证码。
 - 成功返回 `action_token`、`action`、`expires_at`；后续敏感接口以 `X-Action-Token` 携带，Token 只能用于指定动作且单次消费。
-- 错误：`CHALLENGE_EXPIRED`、`CODE_INVALID`、`TOO_MANY_ATTEMPTS`；前端不得把短信验证码或 action token 落普通存储。
+- 错误：`VERIFICATION_RATE_LIMITED`、`CHALLENGE_EXPIRED`、`CODE_INVALID`、`TOO_MANY_ATTEMPTS`；前端不得把短信验证码或 action token 落普通存储。
 
 ### 1.8 实名认证.png
 
@@ -2491,6 +2493,7 @@ X-MeetingIM-APIKey: <预置的普通 API Key>
 | `POST /v1/im/settings/youth-mode/enable` | `{"policy_version":1,"action_token":"action_token"}` | `{"enabled":true,"policy_version":1,"password_set":true,"restrictions":["night_quiet","content_filter","payment_guard"],"updated_at":"2026-08-20T09:00:00Z"}` |
 | `POST /v1/im/settings/youth-mode/disable` | Header `X-Action-Token: action_token`；Body `{}` | `{"enabled":false,"policy_version":1,"password_set":true,"updated_at":"2026-08-20T09:00:00Z"}` |
 | `POST /v1/im/security/challenges` | Header `Idempotency-Key`；Body `{"scene":"close_youth_mode","channel":"sms"}` | `{"challenge_id":"sec_chg_1","phone_mask":"+861****000","expires_in_seconds":300,"resend_after_seconds":60}` |
+| `POST /v1/im/security/challenges` 限流 | 同上 | HTTP `429`：`{"code":30020,"reason":"VERIFICATION_RATE_LIMITED","message":"verification rate limited","details":{"challenge_id":"sec_chg_1","retry_after_seconds":45}}`；小时限流时 `retry_after_seconds` 可能为数百/数千秒且可不返回 `challenge_id` |
 | `POST /v1/im/security/challenges/{id}/verify` | `{"code":"123456"}` | `{"action_token":"action_token","action":"close_youth_mode","expires_at":"2026-08-20T09:05:00Z"}` |
 | `GET /v1/im/security/realname` | Query only | `{"status":"unverified","can_submit":true}` |
 | `POST /v1/im/security/realname/submissions` | `{"name":"张三","id_type":"cn_id","id_number":"110101199001011234"}` | `{"submission_id":"rn_1","status":"pending","can_submit":false}` |