1. [spec] [apps/go/main.go:114](/home/paulca/amadan.net/carlos/todomvc-bakeoff/.worktrees/go/apps/go/main.go:114): `checkLoopback` accepts any loopback address, including `127.0.0.2` and `::1`. The brief explicitly requires binding only to `127.0.0.1`. These alternative `--listen` addresses pass validation and start a listener; restrict validation to the required address.