pnpm self-update only replaces the pnpm binary — it does not update
other files in the @pnpm/exe package (setup.js, pn, pnpx, pnx all
remain from the v10 bootstrap). So @pnpm/exe/pn may not exist at all.
Instead of relying on @pnpm/exe/pn, create the aliases directly:
- pn → symlink to the pnpm binary
- pnpx/pnx → shell scripts that exec "pnpm dlx"
Also remove the setup.js call after self-update since it's no longer
needed and would run the v10 version which doesn't know about pn.
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