Fix registration OTP anchor and batch task state

docs/reviews/TASK-5-VALIDATION-2026-03-23.md

@@ -0,0 +1,29 @@
+# Task 5 Validation - 2026-03-23
+
+## Scope
+
+- Task 5
+- OTP timeout backoff handling
+- Registration controller backoff state persistence
+
+## Commands
+
+1. `./.venv/bin/python -m pytest tests/test_registration_email_service_failover.py tests/test_registration_otp_phase.py`
+   - exit code: `0`
+   - result: `4 passed`
+   - notes: 存在项目既有的 SQLAlchemy / Pydantic / FastAPI deprecation warnings，本次任务未改动相关代码路径。
+
+2. `./.venv/bin/ruff check src/services/base.py src/web/routes/registration.py tests/test_registration_email_service_failover.py`
+   - exit code: `127`
+   - result: failed
+   - notes: `.venv/bin/ruff` 不存在。
+
+3. `./.venv/bin/python -m ruff check src/services/base.py src/web/routes/registration.py tests/test_registration_email_service_failover.py`
+   - exit code: `1`
+   - result: failed
+   - notes: 虚拟环境未安装 `ruff` 模块，未完成 lint 校验。
+
+## Summary
+
+- 回归测试通过，覆盖 `OTP_TIMEOUT_SECONDARY` 连续 3 次失败进入 `3600s` 深度冷却。
+- Lint 校验因环境缺少 `ruff` 未执行。