Search-click window: buffer both sides, close by watermark, correct or drop Diagram

Event-time accumulation

The window opens on event time and accumulates timestamped searches and clicks
Either side may arrive first; the per-session buffers hold both until they meet
A restart replays the input log by event time, so the rebuilt window is identical

Watermark discipline

The watermark is a threshold per upstream partition, advanced by the minimum
An idle partition is parked after a timeout so it cannot hold every window hostage
Parking is explicit and metered, never a silent exclusion

Two late policies

Inside allowed lateness a laggard publishes a correction that retracts the old value
Beyond the horizon it is dropped and counted, with an alert when the fraction grows
The lateness budget comes from the measured lateness distribution, not a guess