SYNC-01: define authenticated save bundle contract - #648

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@1bd1e32a3bdc45362d1e726936510720a7c30a57. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/