Help request: upgrade failed, locked out at decryption passphrase

[wibble]

Whether you can "easily" fix it is going to depend on what got broken. I don't know what tools are available on jumpdrive once you telnet into it either - you may be better using another distro booted from uSD if jumpdrive is missing tools. If you're lucky you can mount the eMMC rootfs then chroot into it and rerun the apt upgrade or dist-upgrade to complete the process. I'm not certain what will happen if it tries updating the bootloader in this case though. There are a load of guides on chrooting for repair like the one below:
https://www.turnkeylinux.org/docs/chroot...air-system