Upload error

### Describe the bug
Was uploading mkv files to my server and kept failing to finilize upload

### To Reproduce
Uploaded half a file, then it got renamed on client machine and stopped uploading. So I aborted it using the fire extinguisher. Then tried to upload with the new name, but failed after hash due to half uploaded file already existing. Reverted the name of the file and then uploaded it again and now this has happened.

### Expected behavior
A file to be uploaded

### Screenshots

### Server details (if you are using docker/podman)
remove the ones that are not relevant:
* **server OS / version:** Ubuntu 24? (maybe different version, but it's a LTS server varient)
* **how you're running copyparty:** docker
* **docker image:** latest as of July 17th, 2026
* **copyparty arguments and/or config-file:**

### Client details
if the issue is possibly on the client-side, then mention some of the following:
* the device type and model: PC (custom build)
* OS version: Win 10
* browser version: Opera GX

### Server log
if the issue might be server-related, include everything that appears in the copyparty log during startup, and also anything else you think might be relevant

### Additional context
When uploading my .mkv files, it often fails on a handful of segments throught the upload, then finalizes alright afterwards.

该 issue 描述了在重命名并中止的场景之后上传 .mkv 文件失败的问题。查看服务器的上传处理代码，重点可能在文件分块、可恢复上传和基于哈希的去重附近。检查是否存在已有的部分文件，以及服务器如何处理冲突或重命名。上传尝试期间的日志应是首先调查的地方，但该 issue 缺少具体的错误消息或代码指引。

由索引模型根据 Issue 内容生成。