KOPR R217 Custom-elements repair flow

editor mutation
  -> atomic optimistic write
  -> repository generation and stable snapshot
  -> catalogue reconciliation
  -> open-widget impact resolution
  -> selector PREPARE -> COMMIT -> rollback
  -> WStack typed preview
  -> MPC HTTPS/identity trust boundary

Stable snapshot rule
- One repository race: retry.
- Second repository race: publish neither repository nor derived cache.

Identity rule
- Rename publishes old and new identity.
- Delete publishes fallback presence/absence.
- MPC accepts same identity and rejects different identity.

Status
PASS_HEADLESS / fully_qualified false / native-qualification HOLD.