Sideloading a library loan onto a Kobo without Adobe Digital Editions

TL;DR Link to heading Library lending apps hand out .acsm files, which normally need Adobe Digital Editions to turn into a readable epub. ADE doesn’t run on Apple Silicon macOS. I built libgourou from source instead, activated it against my Adobe ID, and downloaded the loan with its acsmdownloader tool. Copying the encrypted epub straight to the Kobo didn’t work: newer Kobo firmware dropped Adobe DRM support entirely, so the device ignores ADEPT-encrypted files with no error and no log line. libgourou also ships adept_remove, a DRM-removal utility, for exactly this kind of dead end. Getting the book to look right in the library then needed a second fix, because Nickel never generates cover thumbnails for sideloaded books.