[loopx-agent]

原结果已经带文件完成回传时，App 保存的消息仍可能没有附件，用户在对话和完整答复页都无法下载。现在从原 Session、Turn、回传路由及已发布结果投影下载入口；下载重新校验不可变快照的大小与 SHA-256，并保留原文件名。相同字节的不同文件也保留各自名称。

复用已有结果发布规则、附件字段和文档组件。原消息、发布凭证及输入附件准入保持原样，浏览不会再次执行 Agent 或发送结果。错会话、来源变化、越界来源和文件损坏有独立负例。

验证：集成最新 main 后，历史回传模块 135 项通过；原飞书结果文件 48 项通过；原回复上下文页面回归通过；打包场景验证两处逐字节下载、中文名称、BOM/CRLF、二进制、键盘、窄屏及英文，零模型 Turn、发送仍为原来的一次；完整 App/Chat 构建及标准预合并 6+13 项通过。初次预合并因本地根目录缺 TypeScript 依赖失败，安装锁定依赖后通过。CI 按当前项目策略不查询或等待。

视觉与数据边界：使用可复现的合成原会话、真实发布和 SQLite/Chat HTTP 及打包 UI。旧版 37aaff7 复现两处缺文件，修复后下载入口直接显示在原答复旁；完整答复与来源详情仍保留。已检查桌面及窄屏画面和 PNG 元数据，无个人对话或私密证据。真实安装采用与原会话验收将在合入后完成。

复现见 docs/development/returned-files-readback.md。

视觉证据 / Visual evidence（修复头 f6ce569f9fbcd860502d98196f9f7b956cd21a55；对照 37aaff7a035d0df18b2166cfe0dc74d5fe04eaf7）：

原版本 / Before	修复后 / After

[mergify]

Hi @loopx-agent, the DCO Sign-off check did not pass. Please inspect
its details first: checkout, fetch, timeout or infrastructure errors
need their own recovery, not a rewrite of otherwise signed commits.

If the log confirms a missing Signed-off-by trailer, amend the
affected commit with git commit --amend -s; for multiple commits,
use an interactive rebase against the current base from the correct
base-repository remote and sign off each affected commit. Push the
rewritten PR branch with git push --force-with-lease origin HEAD.

[loopx-agent]

Replaced by #8476. My manual integration merge lacked its DCO trailer. The replacement contains only the two signed contribution commits and has an identical full source tree; the original branch/history and published evidence remain available. No force push or policy change was used.