I hadn’t realized this about NUT. I just started using it as part of TrueNAS’ built-in UPS monitoring support and haven’t had any issues thus far, but this gives me pause.
I buy that there is room for an alternative tool regardless of how crashy NUT is, but the technology choices for this are a huge turn-off IMO.
I'd just stick the server into a docker container, and firewall it from the public Internet. NodeJS is not something that I'd use for these kinds of tools, but it's not inherently bad.
Then use some rust file where you trust that the compiled file matches the source.