feat(jobs): 增加后台任务运行时

docs/architecture.md

@@ -135,6 +135,18 @@ DevTask 没有"已完成"状态，"已提测"就是终态——开发交付完
 - V2.3：AppData 保存成功后触发关系表同步，让快读路径保持新鲜；同步失败只记日志，不阻塞用户保存。
 - V2.4：领域 CRUD 成为主写入路径，AppData 写桥保留给历史数据和回滚兜底。不要恢复业务 localStorage 缓存，避免线上部署后出现多端数据分叉。
 
+## Background Job Runtime Layer (V2.6)
+
+V2.6 introduces a database-backed background job runtime for server-side refresh work that must not depend on a user opening a page.
+
+- Storage: `background_jobs` stores `type`, `payload`, `dedupe_key`, `status`, `attempts`, `max_attempts`, `available_at`, `locked_by`, `locked_until`, and `last_error`.
+- Dedupe: active jobs (`queued` / `running`) are unique by `(type, dedupe_key)` when `dedupe_key` is present. Services still check first and recover from unique conflicts to stay idempotent under concurrent enqueue.
+- Lease: `JobLockService.claimNext()` uses `FOR UPDATE SKIP LOCKED` and treats expired `running` rows as claimable, so a crashed worker can be recovered by a later worker.
+- Retry: failed handlers are requeued while `attempts < max_attempts`; terminal failures keep `last_error` and move to `failed`.
+- Worker boundary: `BackgroundJobWorker` is a small handler registry and single-job runner. Domain modules register typed handlers and only write through their own services.
+
+This runtime is intentionally DB-backed first. Redis is already available in deployment, but V2.6 jobs need transactional dedupe with domain writes more than high-throughput queue semantics.
+
 ## 生产部署层（2026-07-01）
 
 当前仓库已补齐云服务器生产部署基线：