Stage 6: Cache Infrastructure

[Fortinbra]

Summary

Implement Stage 6 (Cache Infrastructure) for the Ansible-first reboot.

Scope

• Create the caching role
• Establish persistent cache directories (/opt/runner-cache/{nuget,ccache,pico-sdk})
• Set correct permissions (sticky bit for UID safety)
• Extend container hook wrapper to bind-mount caches into containers
• Add environment variables visible inside containers
• Create weekly cleanup cron jobs

Key Capabilities

• NuGet packages persist across jobs (~7-14 min savings per warm run)
• ccache compiler cache persists with LRU limit enforcement
• Pico SDK toolchain persists (11-19 min savings per warm run)
• Hook wrapper extended to inject mounts and env vars

Acceptance

• Cache directories exist at /opt/runner-cache/{nuget,ccache,pico-sdk}
• Sticky bits set for UID-safe access
• Hook wrapper extension created at /opt/runner-hooks/hooks/mounts.js
• Systemd unit includes cache environment variables
• Test job can read/write cache directories
• Environment variables visible inside container
• Cleanup cron jobs configured and executable
• Second role run is idempotent
• Caches persist across multiple job runs