buzz/schema/tables/public/replica_heartbeat.sql

-- ── Replica heartbeat (read-replica freshness fence) ─────────────────────────
-- Portable read-side freshness observation for the replica fence (see
-- crates/buzz-db/src/replica_fence.rs and migrations/0026). Exactly one row;
-- the single-row token UPDATE is the serialization point that makes tokens
-- globally commit-ordered across relay pods. `epoch` detects token resets
-- (restore/re-seed) so a stale retained token can never masquerade as fresh
-- coverage. Deployment-global by design: describes replication topology,
-- never tenant data.

CREATE TABLE replica_heartbeat (
    id    smallint PRIMARY KEY CHECK (id = 1),
    epoch uuid     NOT NULL DEFAULT gen_random_uuid(),
    token bigint   NOT NULL DEFAULT 0
) WITH (
    vacuum_truncate = false
);