LoadError: cannot load such file

A native extension failed to build or isn't compiled for your Ruby/platform. 1. `gem pristine <gem>` rebuilds the native extension. 2. For bcrypt / nokogiri on Apple Silicon: `bundle config build.<gem> --with-cflags="-Wno-error=implicit-function-declaration"`. 3. After Ruby upgrade (e.g. 3.2 -> 3.3), `bundle pristine` all gems with extensions.