fn dedup_key(event: &Event) -> (String, u64)Expand description
Build the dedup cache key + extract the version for an event.
Returns ("{kind}|{label}|{hwnd}", version).
kind for HwndDriftDetected is "hwnd_drift_detected:{drift_kind}"
so HiddenSinceOpen and OffMonitor for the same (label, hwnd)
don’t collide (reagent P2 PR #722 round 2).
Unhandled variants are tagged with their serde discriminant
(the event field of the JSON tagged-union) so different
variants don’t share the same __catchall__ key (reagent P1
PR #722 round 1).