build(deps): bump Yarn to 4.18.0

[JamieMagee]

What are you trying to accomplish?

Update Yarn Berry from 4.9.2 to 4.18.0. GitHub's latest-release API reports @yarnpkg/cli/4.18.0, published on 2026-07-29, with draft: false and prerelease: false.

Anything you want to highlight for special attention from reviewers?

Node 24, Corepack 0.34.6, pnpm 11.17.0, npm 11.17.0, and YarnPackageManager are unchanged. This remains a Yarn 4 update, so it does not need package-manager support changes.

How will you know you've accomplished your goal?

The npm updater image built successfully with 51 layers. yarn --version returned 4.18.0 in both the updater and development images.

The focused Yarn tests completed with 208 examples, 0 failures, and 3 pending. All required CI checks pass.

Checklist

• I have run the complete test suite to ensure all tests and linters pass.
• I have thoroughly tested my code changes to ensure they work as expected, including adding additional tests for new functionality.
• I have written clear and descriptive commit messages.
• I have provided a detailed description of the changes in the pull request, including the problem it addresses, how it fixes the problem, and any relevant details about the implementation.
• I have ensured that the code is well-documented and easy to understand.

[Copilot]

Copilot review overview

🟢 Approval recommended

The verified release exists, remains compatible with supported Yarn 4, and focused validation passed.

Review tier: Balanced
Findings: None

What changed in this PR

Updates the npm/Yarn updater image to Yarn Berry 4.18.0 while remaining on supported major version 4.

Changes:

• Bumps the installed Yarn version from 4.9.2 to 4.18.0.
• Leaves other package-manager versions unchanged.

File	Description
npm_and_yarn/​Dockerfile	Updates the Yarn version installed through Corepack.

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