Converge frontend to Yarn Berry with global cache

[dkhalife]

Summary

Converges the frontend/ Node package management to modern Yarn (Berry 4.16.0) configured with a global cache so git worktrees share installed dependencies instead of each re-installing node_modules. Uses only Yarn's built-in features — no bespoke scripts.

Changes

• frontend/package.json: added "packageManager": "yarn@4.16.0" so Corepack activates Berry automatically.
• frontend/.yarnrc.yml (new):
  • nodeLinker: node-modules — keeps a real node_modules so vite/jest/playwright/eslint/tsc work unchanged.
  • enableGlobalCache: true — shared global cache.
  • nmMode: hardlinks-global — hardlink from the global cache so worktrees share inodes.
• frontend/package-lock.json: deleted (stray npm leftover).
• frontend/yarn.lock: regenerated in Berry format via yarn install.
• frontend/.gitignore: replaced the old .yarn/ + .yarnrc.yml ignores with Yarn's standard entries (.yarn/* with ! exceptions for patches/plugins/releases/sdks/versions, plus .pnp.*). .yarnrc.yml is now tracked.

CI / workflows

• frontend-build.yml: added corepack enable step and switched yarn install --frozen-lockfile → yarn install --immutable (Berry equivalent). Kept cache: 'yarn' + cache-dependency-path: frontend/yarn.lock.
• cut-release.yml: added corepack enable; yarn version --patch --no-git-tag-version → yarn version patch (Berry equivalent, no git tag by default).
• full-release.yml: added corepack enable; yarn install → yarn install --immutable.
• .github/copilot-instructions.md: yarn install --frozen-lockfile → yarn install --immutable.

GitHub runners default to Yarn classic v1, which can't read the Berry lockfile, so corepack enable is required before any yarn invocation.

Verification

In frontend/, all pass:

• yarn install / yarn install --immutable (no lockfile drift)
• yarn lint ✅
• yarn tsc ✅
• yarn build ✅
• yarn test ✅ (9 suites, 79 tests)

E2E (yarn test:e2e) skipped — requires browser download.

Note: locally the nmMode was downgraded to hardlinks-local because this session's global cache and worktree live on different drives. On a normal same-device setup hardlinks-global applies as configured.

[Copilot]

Pull request overview

Updates the frontend/ package management and CI to use Yarn Berry (via Corepack) with a shared global cache, aiming to reduce redundant installs across git worktrees while keeping the node_modules linker for tool compatibility.

Changes:

• Pin Yarn Berry via packageManager and add Yarn configuration for global cache + node-modules linker.
• Refresh frontend ignore rules for Yarn Berry artifacts.
• Update GitHub Actions workflows/docs to enable Corepack and use Berry’s --immutable install / yarn version patch.

Show a summary per file

File	Description
frontend/package.json	Pins Yarn Berry via packageManager so Corepack selects the intended Yarn version.
frontend/.yarnrc.yml	Adds Yarn Berry configuration (global cache + node-modules), but includes security-weakening settings that should be removed/narrowed.
frontend/.gitignore	Updates ignore patterns to Yarn Berry’s recommended .yarn/* + exceptions and .pnp.*.
.github/workflows/frontend-build.yml	Enables Corepack and switches install to yarn install --immutable (but Corepack step ordering needs fixing).
.github/workflows/full-release.yml	Enables Corepack and uses yarn install --immutable during release builds.
.github/workflows/cut-release.yml	Enables Corepack and switches to yarn version patch (but should explicitly set up Node).
.github/copilot-instructions.md	Updates frontend install command to yarn install --immutable.

Copilot's findings

• Files reviewed: 7/9 changed files
• Comments generated: 4