Fix cloud sync state consistency and provider-safe conflict handling

docs/DOC-MAINTENANCE.md

@@ -30,6 +30,7 @@ Aspirational / feature-branch content belongs in that branch's docs, or is clear
 | [`design.md`](./design.md) | The design system: theme mechanism, shadcn component selection, new-page recipe; tokens split to [`references/design-tokens.md`](./references/design-tokens.md), component palette to [`references/design-components.md`](./references/design-components.md), layout/motion/state/a11y patterns to [`references/design-patterns.md`](./references/design-patterns.md). |
 | [`verification.md`](./verification.md) | Lightweight end-to-end functional verification — throwaway scratch scripts driving the real built extension; report template split to [`references/verification-report-template.md`](./references/verification-report-template.md), debugging FAQ to [`references/verification-debugging.md`](./references/verification-debugging.md). |
 | [`architecture.md`](./architecture.md) | Deep internals: process model, message passing; subsystem deep-dives split to [`references/architecture-services.md`](./references/architecture-services.md), [`references/architecture-data.md`](./references/architecture-data.md), [`references/architecture-gm-api.md`](./references/architecture-gm-api.md), [`references/architecture-execution.md`](./references/architecture-execution.md), [`references/architecture-build.md`](./references/architecture-build.md). |
+| [`cloud-sync.md`](./cloud-sync.md) | Cloud sync internals: sync files, digest/status semantics, provider differences, error classification, retry policy. |
 | [`translation.md`](./translation.md) | Translation / localization single source of truth. |
 | [`DOC-MAINTENANCE.md`](./DOC-MAINTENANCE.md) | This guide: doc-set organization rules + fact-check / anti-drift discipline. |
 | [`README.md`](./README.md) | The index that points to all of the above. |
@@ -98,7 +99,7 @@ git ls-files eslint-rules/; git grep -l "require-last-error-check" -- eslint.con
 Link integrity — confirm every relative markdown link in the core docs resolves:
 
 ```bash
-for doc in AGENTS.md docs/README.md docs/DOC-MAINTENANCE.md docs/develop.md docs/references/develop-testing.md docs/design.md docs/references/design-tokens.md docs/references/design-components.md docs/references/design-patterns.md docs/architecture.md docs/references/architecture-services.md docs/references/architecture-data.md docs/references/architecture-gm-api.md docs/references/architecture-execution.md docs/references/architecture-build.md docs/verification.md docs/references/verification-debugging.md docs/references/verification-report-template.md docs/translation.md; do
+for doc in AGENTS.md docs/README.md docs/DOC-MAINTENANCE.md docs/develop.md docs/references/develop-testing.md docs/design.md docs/references/design-tokens.md docs/references/design-components.md docs/references/design-patterns.md docs/architecture.md docs/references/architecture-services.md docs/references/architecture-data.md docs/references/architecture-gm-api.md docs/references/architecture-execution.md docs/references/architecture-build.md docs/verification.md docs/references/verification-debugging.md docs/references/verification-report-template.md docs/cloud-sync.md docs/translation.md; do
   # the sed pipeline drops fenced code blocks and inline code spans first, so illustrative sample
   # links inside ```md snippets or `single-backtick` text (e.g. references/verification-report-template.md's
   # screenshot/resource examples, verification.md's "Evidence location" spans) aren't false-flagged as broken

docs/README.md

@@ -11,6 +11,7 @@
 | [`design.md`](./design.md) | 设计系统参考:主题机制、shadcn 组件选型、新建页面配方总览;令牌完整值拆到 [`references/design-tokens.md`](./references/design-tokens.md),组件清单拆到 [`references/design-components.md`](./references/design-components.md),布局/响应式/动效/状态/无障碍范式拆到 [`references/design-patterns.md`](./references/design-patterns.md)。**做页面/对话框/区块前先读。** |
 | [`verification.md`](./verification.md) | 功能验证指南:用一次性 scratch 脚本驱动真实扩展做端到端验证(不跑全量 E2E、不加永久用例);报告模板拆到 [`references/verification-report-template.md`](./references/verification-report-template.md),调试 FAQ 拆到 [`references/verification-debugging.md`](./references/verification-debugging.md)。**验证改动是否真正跑通时读。** |
 | [`architecture.md`](./architecture.md) | 内部原理总览:多进程模型、消息传递;各子系统深入拆到 [`references/architecture-services.md`](./references/architecture-services.md)(服务层)、[`references/architecture-data.md`](./references/architecture-data.md)(数据层)、[`references/architecture-gm-api.md`](./references/architecture-gm-api.md)(GM API)、[`references/architecture-execution.md`](./references/architecture-execution.md)(脚本执行)、[`references/architecture-build.md`](./references/architecture-build.md)(构建管线)。 |
+| [`cloud-sync.md`](./cloud-sync.md) | 云同步实现说明:同步文件语义、主流程、状态合并、provider 差异、错误分类、retry 策略和维护注意事项。 |
 | [`DOC-MAINTENANCE.md`](./DOC-MAINTENANCE.md) | 文档维护与事实核对指南:组织规则、逐条核对清单、一键校验脚本。**改/审文档前先读。** |
 
 ## 翻译 / Translation