Fix only-pnpm to support pnpm 11, and dedupe script

[CraigMacomber]

Description

Fix only-pnpm to support pnpm 11, and dedupe script

Reviewer Guidance

The review process is outlined on this wiki page.

[github-actions]

Hi! Thank you for opening this PR. Want me to review it?

Based on the diff (33 lines, 3 files), I've queued these reviewers:

• Correctness — logic errors, race conditions, lifecycle issues
• Security — vulnerabilities, secret exposure, injection
• API Compatibility — breaking changes, release tags, type design
• Performance — algorithmic regressions, memory leaks
• Testing — coverage gaps, hollow tests

How this works

• Adjust the reviewer set by ticking/unticking boxes above. Reviewer toggles alone don't trigger anything.

• Tick Start review below to dispatch the review fleet.

• After review finishes, tick Start review again to request another run — it auto-resets after each dispatch.

• This comment updates as new commits land; your reviewer selections are preserved.

• Start review

[Copilot]

Pull request overview

This PR updates pnpm enforcement logic and removes a duplicated compatibility-workspace copy of the pnpm-only install guard.

Changes:

• Updates the root only-pnpm.cjs check to use npm_execpath.
• Removes the compat-workspaces-local copy of only-pnpm.cjs.
• Points the compat workspace preinstall script at the root script.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
scripts/only-pnpm.cjs	Updates pnpm detection logic.
packages/test/test-version-utils/compat-workspaces/scripts/only-pnpm.cjs	Removes duplicated pnpm enforcement script.
packages/test/test-version-utils/compat-workspaces/full/package.json	Redirects compat workspace preinstall to the root pnpm enforcement script.

[CraigMacomber]

This package is private, so I don't think it gets installed, but maybe I'm missing something about how its used.

[CraigMacomber]

Anyone know why we have duplicate copies of this script? I think having them all point at the same one would be fine (other than CI being broken for some of server at the moment which would block this PR if I did that here).