feat(agent-harness): memory read→dedupe→write→update-index protocol — rework of #4388 - #4444

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: dorny/paths-filter@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/