fix: a parallel flush worker commits before it pins its output, and the collect loop frees what it did not collect (#1747) - #1748

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache/restore@v4, actions/checkout@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/