Index version lifecycle — index_manifests.state Diagram

activate() only promotes a validated row and retires the current active row in the same connection
Partial unique index one_active_index: never two active rows
--no-activate leaves the new collection validated so it can be calibrated before --activate flips kb_current

register() is an UPSERT: rebuilding an existing version resets that row — even the active one — to building
The Qdrant alias flips before registry.activate(), and mark_failed has no state guard
No transition leaves retired: rolling back means rebuilding, or pointing the alias back by hand