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.

El issue describe un fallo de carga con archivos .mkv después de un escenario de renombrado y cancelación. Examina el código de gestión de cargas del servidor, probablemente en torno a la fragmentación de archivos, las cargas reanudables y la deduplicación basada en hashes. Comprueba si existen archivos parciales y cómo gestiona el servidor los conflictos o los renombrados. Los logs durante los intentos de carga serían el primer lugar que investigar, pero al issue le faltan mensajes de error específicos o referencias al código.

Escrito por el modelo de indexación a partir del texto del issue.