Use Corepack to manage Yarn instead of committed release

[rtivital]

Summary

Yarn is now provided by Corepack from the packageManager field (yarn@4.18.1) in package.json, so the 3.8 MB release file no longer has to live in the repository.

• Remove .yarn/releases/yarn-4.18.1.cjs
• Remove yarnPath from .yarnrc.yml
• Add a corepack enable step to the CI workflow before actions/setup-node, because cache: 'yarn' invokes yarn and would otherwise hit the Yarn 1.x preinstalled on the runner

Local setup

Run corepack enable once per machine. After that yarn resolves to the version pinned in packageManager.

Verification

corepack yarn --version reports 4.18.1 and corepack yarn install --immutable completes on a clean checkout of master.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Align the nested package-manager pin before dropping yarnPath

When a command is run from package/, Corepack selects the closest manifest, so it launches the yarn@4.0.1 pinned in package/package.json rather than the root's 4.18.1; Node's Corepack documentation confirms this closest-manifest behavior. Previously yarnPath redirected that invocation to 4.18.1, but after its removal Yarn 4.0.1 loads the root configuration and rejects newer settings such as approvedGitRepositories and npmMinimalAgeGate, preventing installs and other commands from that workspace. Remove or update the nested packageManager field before dropping this override.

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[chatgpt-codex-connector]

Add Corepack to the local setup instructions

This enables Corepack only in CI, while README.md:8 still tells new template users to run yarn without enabling it—and does so before nvm use. Corepack is opt-in and corepack enable installs its shims next to the active Node binary, as documented in Node's Corepack guide, so after removing the repository-managed Yarn release this onboarding path fails for users without pre-enabled Corepack. Reorder the instructions to run nvm use, then corepack enable, then yarn.

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