pnpm workspaces: the CI cache that survived the fix and cost me 40 minutes per build

Short summary

The author debugged a 40-minute CI build caused by misconfigured pnpm caching in GitHub Actions monorepos—could be 8 minutes with proper setup. Root cause: pnpm dynamically picks store-dir paths between runs, breaking actions/cache restoration. Solution: set fixed PNPM_STORE_PATH environment variable, configure store-dir explicitly, and use proper cache keys with hashFiles('**/pnpm-lock.yaml') to detect nested workspace changes; includes before/after workflows.

• •Monorepo CI cache failures caused by pnpm's dynamic store-dir paths between GitHub Actions runs
• •Solution: set fixed PNPM_STORE_PATH, explicitly configure store-dir, use hashFiles('**/pnpm-lock.yaml') for cache keys
• •Includes detailed before/after GitHub Actions workflows with three critical configuration fixes

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