Fix MessageDeduplicator max_size enforcement

gateway/platforms/helpers.py

@@ -57,6 +57,15 @@ class MessageDeduplicator:
         if len(self._seen) > self._max_size:
             cutoff = now - self._ttl
             self._seen = {k: v for k, v in self._seen.items() if v > cutoff}
+            if len(self._seen) > self._max_size:
+                # TTL pruning alone does not cap the cache when every entry is
+                # still fresh. Keep the newest entries so the helper's
+                # max_size bound is enforced under sustained traffic.
+                newest = sorted(
+                    self._seen.items(),
+                    key=lambda item: item[1],
+                )[-self._max_size:]
+                self._seen = dict(newest)
         return False
 
     def clear(self):