fix: MindSpace remote sync, thumbnail fallback, and Plaza URL guards

Ensure page sync runs via pageSyncService in remote mode, fall back to
workspace HTML when storage assets are missing, and prevent production
Portal from linking to loopback Plaza URLs baked in at build time.

Co-authored-by: Cursor <cursoragent@cursor.com>

AGENTS.md

@@ -24,6 +24,7 @@ bash scripts/check-release-ready.sh
 | 主题 | 文档 |
 |------|------|
 | MindSpace 公开页 `edit_file` 落盘 + 聊天 Finish 不丢消息 | [docs/regression-guards/mindspace-publish-and-chat-finish.md](docs/regression-guards/mindspace-publish-and-chat-finish.md) |
+| MindSpace remote 页面 sync + storage 缺失缩略图 fallback | [docs/regression-guards/mindspace-remote-page-sync-and-thumbnail.md](docs/regression-guards/mindspace-remote-page-sync-and-thumbnail.md) |
 
 索引：[docs/regression-guards/README.md](docs/regression-guards/README.md)
 
@@ -32,6 +33,7 @@ bash scripts/check-release-ready.sh
 ```bash
 npm run verify:mindspace-publish-guards
 npm run verify:mindspace-publish-guards:full
+npm run verify:mindspace-page-sync-guards
 ```
 
 发版脚本（`scripts/release-portal-runtime-prod.sh`）在未 `--skip-tests` 时也会执行相关 verify。
@@ -43,6 +45,8 @@ npm run verify:mindspace-publish-guards:full
 - `conversation-display.mjs` + `src/utils/message.ts` - 用户消息不得展示 routing/skill 内部前缀
 - `src/hooks/useTKMindChat.ts` - `syncSessionMessages` merge + 重试
 - `server.mjs` - session snapshot 需 `hint_mc` 且 `hint_ua` 才走缓存
+- `mindspace-pages.mjs` - storage 缺失时 HTML 页回退读 workspace `relative_path`
+- `mindspace-page-sync-service.mjs` + `server.mjs` - remote 模式也必须 sync public HTML
 
 代码内搜索 `REGRESSION GUARD` 可定位所有内联说明。
 
@@ -52,6 +56,11 @@ npm run verify:mindspace-publish-guards:full
 - `chat-finish-sync.test.mjs`
 - `conversation-display.test.mjs`
 
+### MindSpace page sync + thumbnail
+
+- `mindspace-page-sync-service.test.mjs`
+- `mindspace-pages.test.mjs`
+
 ## Cursor 专用规则（其它工具请读上文文档）
 
 Cursor 额外加载：`.cursor/rules/mindspace-publish-chat-finish-guards.mdc`