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RUNBOOK §15: dual-boot operation — Linux⇄Windows switch procedure, per-OS CI-stack table (roots/runner/vmrun), current GRUB behaviour (DEFAULT=0, TIMEOUT=0 hidden → boots straight to Linux), post-boot verification commands for both OSes, and an optional GRUB tweak (left unapplied — boot-to-Linux is intentional so the box returns as the Linux CI host after any unattended reboot). Checklist: Passo 9 done; fixed the stale global tracking table (Passi 6–9 were still [ ] despite being complete). Phase B is now fully closed (1–9 [x]). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>