d98b32640b
The per-cluster contact map only gains a key when a row parses, so an all-malformed cluster has no key at all and is caught by the absent-key arm; the empty-set guard is defensive/unreachable for the DB producer. Comment-only (Task 4 code-review minor follow-up). Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW