A lil bit off-topic but i have stumbled on a problem with "kernel panic Attempted to kill init! exitcode=0x00000200"
The problem was unrelated because after failed update i was missing package zfs-initramfs in my initramfs
I have swapped HBA controller, disk UUIDs got mixed up. The system had started on currently installed kernel no problem. The problem with UUIDs resurfaced aftersmoe time when I tried to update the system (apt update ^^ apt upgrade) and the krenel updated from 6.17 to 7.0. APT (or rather proxmox-boot-tool) was unable to install on efi partitions.
According to some other forum posts i have cleared /etc/kernel/proxmox-boot-uuids and reinstalled kernels with apt reinstall... And restarted...
Ant thats how i have broken my clusters node...
In order to diagnose the problem I was using this thread's chroot instructions. They are incorrect because /run isn't mounted properly in chroot. Additionally efivars mount is missing. Finally i was able to install missing zfs-initramfs package after booting from proxmox 9.1 installer. From the boot menu i have chosen 'Advanced options' then 'Instal Proxmox VE (Terminal UI, Debug mode)' and booted into initramfs of the installer. I have typed 'exit' in initramfs prompt and then real bash prompt appeared...
Then I have started configuring chroot environment.
I have started with zpool import -f -R /mnt rpool
This got me with the system with acces to all my nodes files. Than I have configurred the network by copying /mnt/etc/netwotk/interfaces to /etc/network/interfaces and editiing it to match diffetent NIC names in the installer (i have only public IP address with IP routeon each node - no dhcp). After I was able to ping 8.8.8.8 I have proceeded to actual chroot bootstrapping:
cd /mnt
mount -t proc proc proc
mount -t sysfs sys sys
mount -o bind /dev dev
mount -t devpts pts dev/pts
mount -t tmpfs tmpfs tmp
mount -o bind /run run
mount -o bind /run var/run
mount -t efivarfs efivarfs sys/firmware/efi/efivars
chroot /mnt /bin/bash
Previous post mixed binding absolute path of source for '/run' with relative path of target '/mnt/run' (i'm ashamed how much time it took me to realise this simple typo). Additionally to run proxmox-boot-tool init in EFI environment you need to mount efivarfs.
After this I had network and fully bootstrapped chroot environment and i was able to reinstall kernel, add missing zfs-initramfs and update both initramfs (only in this configration i was able to run update-initramfs -u -k all and dont have some kind of error) and EFI + GRUB.
Yay, system is up after 16 hours of fumbling around error code 0x00000200