chore: upgrade repository to pnpm 12

[antonvishal]

why

pnpm 12 rewrites the package manager in Rust while retaining pnpm 11's commands, settings, and lockfile compatibility.

For Stagehand's common workflows, pnpm 12.1 is 45% to 65% faster than pnpm 11.10.

what changed

• Upgrade repository tooling from pnpm 11.10.0 to pnpm 12.1.0.
• Update CI, preview, and release workflows to install pnpm 12.1.0.
• Keep source examples compatible with pnpm 11.10.0 or newer.

benchmark

Store	node_modules	Scripts	pnpm 11.10	pnpm 12.1	Change
Warm	Present	Disabled	172 ms	63 ms	63.3% faster
Cold	Present	Disabled	172 ms	60 ms	65.1% faster
Warm	Absent	Disabled	5.530 s	3.034 s	45.1% faster
Cold	Absent	Disabled	37.403 s	39.661 s	6.0% slower
Warm	Absent	Enabled	6.457 s	2.547 s	60.6% faster
Cold	Absent	Enabled	38.359 s	42.271 s	10.2% slower

The main results:

• Existing installations complete 63% to 65% faster.
• Clean installs from a warm store complete 45% faster with scripts disabled.
• Clean installs with lifecycle scripts complete 61% faster.
• The package contract test improved from a 3.36-second median to 2.54 seconds, or 24.3%.
• Fully cold installs were 6% to 10% slower because registry transfer dominated the result.

test plan

• pnpm install --frozen-lockfile
• pnpm build
• pnpm test
• pnpm exec vitest run packages/sdk-ts/tests/packageContract.test.ts
• pnpm fmt:check
• git diff --check

---

Summary by cubic

Upgrades the repository from pnpm 11.10.0 to pnpm 12.1.0, which is significantly faster for common workflows. Existing installs run 45–65% faster, and clean installs from a warm store are 45–61% faster, with a minor slowdown on fully cold installs.

Details

• Updates all CI, preview, and release workflows to install pnpm 12.1.0.
• Regenerates the lockfile and updates devEngines.packageManager in package.json.
• Relaxes documentation requirements from exact pnpm 11.10.0 to "11.10.0 or newer" to keep source examples compatible.
• Updates the package contract test to use pnpm 12.1.0.

^{Written for commit b3f59fe. Summary will update on new commits.}

[changeset-bot]

⚠️ No Changeset found

Latest commit: b3f59fe

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[github-actions]

This PR is from an external contributor and must be approved by a stagehand team member with write access before CI can run.
Approving the latest commit mirrors it into an internal PR owned by the approver.
If new commits are pushed later, the internal PR stays open but is marked stale until someone approves the latest external commit and refreshes it.