Function warn_if_data_lake_schema_stale 

pub async fn warn_if_data_lake_schema_stale(pool: &Pool<Postgres>)

Warns when the connected database is behind LATEST_DATA_LAKE_SCHEMA_VERSION.

execute_migration only runs from telemetry-ingestion-srv/micromegas-monolith; a flight-sql-srv/analytics-web-srv process reads the same database without ever migrating it. On a schema that already has the audience_grants table (v7+) but predates the v9 seed rows, AudienceReadPolicy resolves every audience to an empty grant set rather than erroring, so queries silently return zero rows – this is the only signal an operator gets otherwise.