fix(chess): flag flag-fall on a running clock in PlayerClock::time_out()

backend/modules/chess/src/time_control.rs

@@ -68,6 +68,41 @@ impl PlayerClock {
     }
 
     pub fn time_out(&self) -> bool {
-        self.remaining_time.is_zero()
+        self.get_real_time_remaining().is_zero()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn stopped_clock_reports_timeout_when_remaining_is_zero() {
+        let mut clock = PlayerClock::new(Duration::from_secs(0));
+        assert!(clock.time_out());
+
+        clock.set_remaining_time(Duration::from_secs(10));
+        assert!(!clock.time_out());
+    }
+
+    #[test]
+    fn running_clock_flags_when_it_runs_past_zero_on_the_mover() {
+        // Player on the move with almost no time left, clock running.
+        let mut clock = PlayerClock::new(Duration::from_millis(1));
+        clock.start();
+        // The mover sits on the running clock past zero without moving.
+        std::thread::sleep(Duration::from_millis(5));
+
+        // remaining_time is untouched until stop(), so the raw field is still
+        // non-zero; flag-fall must be detected via the real remaining time.
+        assert!(!clock.remaining_time.is_zero());
+        assert!(clock.time_out());
+    }
+
+    #[test]
+    fn running_clock_with_time_left_is_not_flagged() {
+        let mut clock = PlayerClock::new(Duration::from_secs(60));
+        clock.start();
+        assert!(!clock.time_out());
     }
 }