"Installation successful"—but it doesn't work: 10 places where things go wrong silently between "installing" and "running" a package

Both pip install and pnpm add finished with success on the last line. The names are in the lock file, too. Yet, when I run it ...

It's just luck that it works — 74.5% of 455 AI libraries were importing dependencies not listed in requirements.txt

Yet, it's a ModuleNotFoundError in CI. When you ask an AI agent to 'set this up and run it,' it stops at the very first step.