How to properly protect .bash_history against truncation?

What can I do so that my .bash_history is only aver appended to? I am working in a lot of environments, like singularity, apptainer, docker, podman and ssh with various settings and mounts. Each of the environments may have different HISTFILESIZE value, there might be something in /etc/profile.d on different machines, and I have my own HISTFILE=.bash_historymy HISTFILESIZE="" HISTSIZE="" set in my ~/.bashrc and ~/.profile and ~/.bash_profile. The problem is, if _one_ of the environments happens to set HISTFILESIZE, bam - my .bash_history is lost. I am setting my own HISTFILESIZE in my .bashrc, but if I happen to source /nfs/my/friends/.profile or other scripts they will override HISTFILESIZE and not touch HISTFILE, so still my separate HISTFILE will be truncated. Once it happens, I lose my history. This has happened to me many times throughout the years on various systems and environments. What I had, for quite some time, is a script in ~/.bashrc that would create a number of .bash_history backups and rotate them, this was accompanied with some size checking, like:

name="$(basename "$HISTFILE")"
backupdir=~/.cache/bash_history/
mkdir -p "$backupdir"
file="$HISTFILE"
for ((i=1;i<5;++i)); do
   cp "$file" "$backupdir/$name.$i"
   file="$backupdir/$name.$i"
done

So I would have 5 "sessions" to restore the history file or backup it or "cat" it together. I feel like this was an unsatisfactory temporary solution. Is there a proper solution to protect against bash truncating .bash_history? I would imagine one could run "diff" against old and new one and only merge the missed chunks from the back of .bash_history. I do not think making .bash_history a fifo is a good solution. For example, I would be happy if a shell would "restore" the lost truncated commands on the next ~/.bashrc run from a backup file.