A source that stops emitting, a partition that goes empty, a drift that becomes a dropped field, and a rebuild rehearsal that was never run all produce no error anywhere else on this grid.
Each is therefore an alarm on an absence: a declared quiet period per source binding, not a threshold on a rate.
The divergence rate from continuous reconciliation is the single number that says whether the index still matches the world.
Decisions
Freshness is measured end to end per lane, from source commit to searchable, not as consumer lag — because consumer lag can be zero while the index is wrong.
Every response carries the index version and freshness it was served at, which makes a staleness complaint reproducible.
The query-to-write cost ratio per index is published to tenants, because an index maintained more eagerly than it is read is the cheapest saving available.
