Upload fails with `ENOTSUP: operation not supported on socket, chmod '/data/uploads/...'` (tus PATCH 500)

Uploading an epub through the web UI fails partway through with: tus: unexpected response while uploading chunk, originated from request (method: PATCH, url: http://localhost:8001/api/v2/books/upload/<id>.epub, response code: 500, response text: Something went wrong with that request ENOTSUP: operation not supported on socket, chmod '/data/uploads/<uuid>/<filename>.epub'.

Resolution: The tus upload succeeds in writing the chunk but then fails when the server tries to chmod the finished file, and the request returns 500. This is a host filesystem/permissions problem, not a Storyteller bug: correcting the PUID/PGID the container runs as (so it actually owns /data/uploads) resolved it. Check that the UID/GID in your compose file matches the owner of the host directory bound to /data, and that the directory is writable by it. If the ids are right, the other common cause of ENOTSUP on chmod is a bind mount backed by a filesystem that cannot represent Unix permissions — an SMB/CIFS, NFS with restrictive options, or FUSE-mounted share; move the data directory to local storage or mount it with options that support ownership and mode bits.