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Sync workers proxied a full `ReplicationPresenceSetState` call to the presence writer on every sync request with `affect_presence=True` (via `user_syncing`), and a `ReplicationBumpPresenceActiveTime` call on every user action, even though the writer's presence timers only need feeding every `SYNC_ONLINE_TIMEOUT` / `LAST_ACTIVE_GRANULARITY`. On busy clients this amounts to tens of no-op replication calls per user per minute, and the resulting per-update work is the dominant CPU cost on saturated presence writers. Track the last relayed `(state, timestamp)` per `(user, device)` on the worker and suppress unchanged sync-driven repeats within a 25s relay interval - deliberately below `SYNC_ONLINE_TIMEOUT` (30s) so the writer's device `last_sync_ts`/`last_active_ts` timers stay fed and users neither flap offline nor bounce `currently_active`. Genuine state changes are relayed immediately, explicit (non-sync) set_state calls always go through and reset the throttle, bumps that might un-idle a device bypass it, and entries are evicted when a `USER_SYNC` stop is sent so reconnecting devices are relayed afresh. This gives the writer-CPU benefit that deployments currently obtain by tightening `rc_presence` to ~1/29s, without dropping real presence transitions. --------- Co-authored-by: Claude Fable 5 <noreply@anthropic.com> Co-authored-by: Quentin Gliech <quenting@element.io>