Hello Peter,
you described Foreman workflow correctly, we assume that hosts always boot from network. There is this nasty trick to chainload from disk via grub2 in EFI mode to allow that. We don’t provide any functionality to modify boot loaders either for BIOS or EFI in order to set hosts for reprovisioning.
This would require Foreman being able to manage host BIOS entries and/or EFI entries remotely. This is a huge task, every single vendor has a different protocol. While there are some common APIs like IPMI, it’s not very reliable but some users might do this and there might be even some Foreman plugin I am not aware of.
Well, we see someone asking for this from time to time, but as I described earlier this is not en easy job to implement. Unless you have some idea doing different approach - let me ask then: how you would like this to work?