[plan] Node disk self-healing: no node ever fills

_Automatically composed from the parent epic at dispatch time._

Split by the Architect's C1–C6 components: 6 coders (5762–5767), phase 1 = CP gate, reclaim, gha-user removal, plugin root (needs C2), console (needs C1); phase 2 = retire cron + prove. Added: GET disk-events serves `detail`; C2 must check activation.