change that oldest_active_game_age_sec not gets inflated when redis already deleted it

server/metrics/ServerMetricsCollector.py

@@ -108,6 +108,36 @@ class ServerMetricsCollector:
 
   # ── snapshot builders ─────────────────────────────────────────────────────
 
+  def _calc_active_game_stats(self, game_last_seen_unix:dict) -> tuple[int, int, int]:
+    """Returns (report_active_games, report_stale_candidates, oldest_active_age_sec)."""
+    now = int(time.time())
+    stale_candidates = sum(
+      1
+      for last_seen in game_last_seen_unix.values()
+      if now - last_seen >= self._stale_game_timeout_sec
+    )
+
+    if self._game_state_backend_is_redis:
+      # Redis auto-expires stale keys via TTL, so stale games are already gone from the
+      # server's perspective. We exclude them from all metrics so we only report games
+      # that are actually still alive in Redis.
+      report_active_games = len(game_last_seen_unix) - stale_candidates
+      report_stale_candidates = 0
+      # Only include non-stale timestamps when calculating the oldest active game age,
+      # so a game that Redis already deleted doesn't inflate the age metric.
+      active_last_seen = [
+        last_seen
+        for last_seen in game_last_seen_unix.values()
+        if now - last_seen < self._stale_game_timeout_sec
+      ]
+    else:
+      report_active_games = len(game_last_seen_unix)
+      report_stale_candidates = stale_candidates
+      active_last_seen = list(game_last_seen_unix.values())
+
+    oldest_active_age = max(0, now - min(active_last_seen)) if active_last_seen else 0
+    return report_active_games, report_stale_candidates, oldest_active_age
+
   def build_local_snapshot(self, game_last_seen_unix:dict, game_move_counts:dict) -> dict:
     games_ended = self._metrics['games_ended']
     total_moves = self._metrics['total_moves']
@@ -117,23 +147,7 @@ class ServerMetricsCollector:
       self._metrics['move_response_time_ms_total'] / total_moves if total_moves else 0.0
     )
 
-    now = int(time.time())
+    report_active_games, report_stale_candidates, oldest_active_age = self._calc_active_game_stats(game_last_seen_unix)
-    oldest_active_age = (
-      max(0, now - min(game_last_seen_unix.values())) if game_last_seen_unix else 0
-    )
-
-    stale_candidates = sum(
-      1
-      for last_seen in game_last_seen_unix.values()
-      if now - last_seen >= self._stale_game_timeout_sec
-    )
-
-    if self._game_state_backend_is_redis:
-      report_stale_candidates = 0
-      report_active_games = len(game_last_seen_unix) - stale_candidates
-    else:
-      report_stale_candidates = stale_candidates
-      report_active_games = len(game_last_seen_unix)
 
     return {
       **self._metrics,