Problem

When sending a book via email with "Embed metadata in sent files" enabled and a split library configuration, the send fails with:

ERROR {cps.tasks.mail:137} [Errno 2] No such file or directory: '/tmp/calibre_web/<uuid>.epub'
ERROR {cps.tasks.mail:269} The requested file could not be read. Maybe wrong permissions?

The user sees "Attachment not found" in the task list.

Root Cause

In _get_attachment() in cps/tasks/mail.py, when config_embed_metadata is enabled, do_calibre_export() is called to create a temporary EPUB with embedded metadata. If the export fails to produce a file (e.g. due to a transient NFS issue, a missing book file, or a calibredb export error), do_calibre_export() still returns a path via its fallback:

# Fallback to original behavior
return tmp_dir, temp_file_name

_get_attachment() then unconditionally overwrites datafile with this non-existent temp path:

data_path, data_file = do_calibre_export(self.book_id, extension)
datafile = os.path.join(data_path, data_file + "." + extension)

The original datafile (which pointed to the actual book file on disk and would have worked) is lost. The open() call fails and the send is aborted entirely.

Expected Behavior

If metadata embedding fails, the send should fall back to the original book file rather than failing completely. A book sent without re-embedded metadata is better than a book not sent at all.

Environment

• CWA latest (2026-03-28)
• Split library: config_calibre_split = 1, metadata.db on local volume, book files on NFS
• config_embed_metadata = 1
• config_binariesdir = /usr/bin