The init-nix.sh script previously hardcoded /usr/bin/bash as the login shell
for the 'nix' user, which exists on Arch but not on Debian. This caused the
Nix single-user installer (run via `su - nix`) to fail silently or break in
unpredictable ways on Debian-based images.
We now resolve the shell dynamically via `command -v bash` and fall back to
/bin/sh on minimal systems. This makes Nix installation deterministic across
Arch, Debian, Ubuntu, Fedora, CentOS and CI containers.
https://chatgpt.com/share/6939e97f-c93c-800f-887b-27c7e67ec46d