CI caught this on Node 22 while it passed here on 26. `new File([blob],
…)` only puts the blob's contents in the file where that implementation
recognises a Blob as a part; where it does not, it stringifies it, and
the file contains the thirteen characters "[object Blob]". No error
anywhere -- the name, the type and the attachment are all correct and
the contents are gone.
A browser would not have done this. It is worth not relying on that: an
ArrayBuffer is a part on every implementation, and the whole file is in
memory a moment later regardless, since it is about to be uploaded.