`pnpm self-update` installs the target pnpm into the global packages
directory and links it into PNPM_HOME. It never touches the Homebrew
keg, so a Homebrew user ended up with a second pnpm that the Homebrew
binary on PATH kept shadowing. The update reported success while
`pnpm -v` stayed the same, and later runs declined because the target
was "already installed globally".
Both CLIs now detect a running pnpm that lives inside a Homebrew keg
(`<cellar>/pnpm/<version>/` or `<cellar>/pnpm@<major>/<version>/`) from
its canonical path and fail with ERR_PNPM_CANT_SELF_UPDATE_IN_HOMEBREW,
pointing at `brew upgrade <formula>`. The check sits next to the
existing Corepack refusal, before project config is loaded.
Closes https://github.com/pnpm/pnpm/issues/16547
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Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
