prepare_launch returned early for any process running under the
updater's own claim, so it would not re-run the completion tail. That
also covered processes the updater spawns before PM commits a
generation (a restarted gateway), which then booted with no
environment: previously on the pre-PM venv, now refused.
Under the updater's claim with nothing committed, sync the dependency
generation (carrying the legacy venv's extras, as the first sync
always has), skip the tail since that belongs to the updater, and
relaunch on the store Python. The relaunched process sees the commit
and returns early as before, so the no-recursion guard still holds.
3a42f0fe10