From 1cb9fabadeeb2a6e259a5031cdc5bffbb9680b25 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Fri, 19 Jun 2026 11:36:46 +0100
Subject: [PATCH] Comment why as i64 is safe

---
 rust/src/events/serialize.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/rust/src/events/serialize.rs b/rust/src/events/serialize.rs
index de8847a038..758fd103f3 100644
--- a/rust/src/events/serialize.rs
+++ b/rust/src/events/serialize.rs
@@ -584,6 +584,9 @@ fn serialize_event_value(
         if let Some(sticky_duration) = event.sticky_duration() {
             // min() ensures the origin server can't claim a time in the future
             // to exceed the stickiness duration limit.
+            //
+            // The `as i64` cast is safe as sticky duration are capped to an
+            // hour, which is well within the i64 range.
             let expires_at = std::cmp::min(event.origin_server_ts(), time_now_ms)
                 + sticky_duration.as_millis() as i64;
             if expires_at > time_now_ms {