Mostly the performance cost of thrown exception is under my resolution. If this kind of performance is important, I don't use Ruby at all.

When we quantify "expensivnes", its much cheaper than datbase query or http request. Imho the more important aspect is ensuring security, correctness amd DX. It's much better to throw runtime exception, than have security hole because someone somewhere forgot to check flag in return value.

I don't think the Ruby is the right ecosystem where to enforce this paradigm. Why not use elixir (or something similar), if you want this kimd of rules?

What about ActiveRecord::RecordNotFound ?

Some of people I like followed moved here. Their thoughts are worth an extra icon on the screen.