diff --git a/server-rs/crates/module-runtime/src/membership/cycle.rs b/server-rs/crates/module-runtime/src/membership/cycle.rs
index 306f8afab..2b29f37e6 100644
--- a/server-rs/crates/module-runtime/src/membership/cycle.rs
+++ b/server-rs/crates/module-runtime/src/membership/cycle.rs
@@ -34,9 +34,9 @@ pub fn beijing_local_micros(year: i32, month: u8, day: u8, time_of_day_micros: i
     }
     Some(
         days_from_civil(year, month, day)
-            .saturating_mul(PROFILE_RUNTIME_DAY_MICROS)
-            .saturating_add(time_of_day_micros)
-            .saturating_sub(PROFILE_TASK_BEIJING_OFFSET_MICROS),
+            .checked_mul(PROFILE_RUNTIME_DAY_MICROS)?
+            .checked_add(time_of_day_micros)?
+            .checked_sub(PROFILE_TASK_BEIJING_OFFSET_MICROS)?,
     )
 }
 
@@ -119,6 +119,13 @@ mod tests {
         );
     }
 
+    #[test]
+    fn beijing_local_micros_rejects_overflowing_year() {
+        // 中文注释：超出 i64 微秒范围的年份必须返回 None，而不是饱和成看似合法的值。
+        assert_eq!(beijing_local_micros(1_000_000, 1, 1, 0), None);
+        assert_eq!(beijing_local_micros(-1_000_000, 1, 1, 0), None);
+    }
+
     #[test]
     fn advance_months_clamps_to_month_end() {
         // 中文注释：1/31 开通 → 2/28（2026 非闰年）→ 3/31，每期都从原始锚点重算。