Separate search execution failure from passage-selection failure

When a retrieval system returns no evidence, first determine whether the query executed. Verify the production call path, deployed function or adapter version, authorization boundary, index availability, and a bounded direct invocation before tuning ranking. A timeout or pre-evidence exception is an execution failure; a completed query that returns the wrong session is candidate selection failure; a correct session with the wrong excerpt is passage-selection failure.

Fix and deploy the earliest failing layer, then rerun the same query and source-open checks before claiming improvement. Existing indexes or a tested adapter do not prove production traffic uses that path, and a successful deployment does not establish answer-bearing passage delivery.