FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory

Why this happens

• A large build (webpack, Vite, `tsc`) genuinely needs more heap than Node's default limit allows
• Jest or Vitest runs too many workers at once, and together they exhaust the runner's memory
• A memory leak in the tests (unclosed servers, global caches, huge snapshot or fixture files) keeps growing across the run

How to fix it

1. Raise the heap limit for that job: `NODE_OPTIONS=--max-old-space-size=4096` (in MB), staying below the runner's real memory
2. Limit parallel workers in CI (`jest --maxWorkers=2`, or `--workerIdleMemoryLimit` to recycle workers that grow too large)
3. If memory keeps climbing over the run, look for the leak with `--logHeapUsage` instead of just raising the limit

Example

              # GitHub Actions
- name: Build
  run: npm run build
  env:
    NODE_OPTIONS: --max-old-space-size=4096