[watcher] trim idempotency comment

Replace 4-line block with a 1-line comment to match the rest of the file.

Author: 0xsiddharthks

crates/hashi/src/onchain/watcher.rs

@@ -451,10 +451,7 @@ async fn handle_events(
                 // Advance uses the event's checkpoint timestamp (~sign-time)
                 // rather than `txn.timestamp_ms` (creation time) to stay in
                 // lockstep with the guardian's `last_updated_at`.
-                // `signatures.is_some()` makes the apply idempotent — set
-                // here on the first observation and by `scrape_hashi` at
-                // bootstrap, so checkpoint redelivery and bootstrap-replay
-                // events are skipped.
+                // Gate on `signatures.is_none()` for idempotency across checkpoint redelivery and bootstrap replay.
                 let (limiter_inputs, pick_to_sign_ms) = {
                     let mut state = state.state_mut();
                     state