I hate to ask this because I feel like I'm missing something obvious. When I changed the shell to bash for root, I get the default bash prompt (bash-5.2# ). No problem, right - just change it in /etc/profile or even ~/.profile. Heck, maybe even add a custom prompt to /etc/shinit or ~/.shinit for good measure too. None of that worked though. The only thing that worked was adding the prompt to ~/.bashrc.
So what am I missing? How do I get the prompt to change for the login shell and not the interactive shell?