D47 / R-1269 (P2): a new install never writes into an earlier install's backup — every install has an identity (install_id), the unit records it, every unit writer asks first; another install's unit is set aside whole (backups/set-aside/<app>/<stamp>, a D25 kept copy, „Visszaállítás” + „Eltávolítás” on the restore page); a move that fails refuses the write. Red-proved. Commit only.

controller/internal/backup/update_guard.go

@@ -406,6 +406,9 @@ func (m *Manager) RunAppBackupNow(ctx context.Context, stackName string) error {
 		if err != nil {
 			return util.MsgError("err.backup.adatbazis_felderites_sikertelen", err)
 		}
+		if gErr := m.guardUnitWrite(stackName, nsRoot, "update pre-backup"); gErr != nil { // D47 (R-1269)
+			return util.MsgError("err.backup.adatbazis_mentes_sikertelen", stackName, gErr)
+		}
 		dumped := 0
 		for _, db := range dbs {
 			if db.StackName != stackName {