refactor: use public max_size property for offline-queue retention

Prefer MessageQueue.max_size (new public property in openhop_core) over
the private _max_size attribute, keeping a getattr fallback for older
cores that predate the property.

repeater/companion/frame_server.py

@@ -61,13 +61,18 @@ class CompanionFrameServer(_BaseFrameServer):
     async def _persist_companion_message(self, msg_dict: dict) -> None:
         """Persist message to SQLite and pop from bridge queue.
 
-        The bridge's ``offline_queue_size`` (``message_queue._max_size``) doubles
+        The bridge's ``offline_queue_size`` (``message_queue.max_size``) doubles
         as the SQLite retention limit: 0 disables offline storage entirely, so the
         message is dropped instead of persisted.
         """
         if not self.sqlite_handler:
             return
-        retention = getattr(self.bridge.message_queue, "_max_size", None)
+        # Older cores predate the public max_size property.
+        retention = getattr(
+            self.bridge.message_queue,
+            "max_size",
+            getattr(self.bridge.message_queue, "_max_size", None),
+        )
         if retention == 0:
             self.bridge.message_queue.pop_last()
             return

tests/test_companion_settings.py

@@ -251,7 +251,7 @@ class TestPersistSkipWhenOff:
         fs.sqlite_handler = MagicMock()
         fs.companion_hash = "0x01"
         bridge = MagicMock()
-        bridge.message_queue._max_size = max_size
+        bridge.message_queue.max_size = max_size
         fs.bridge = bridge
         return fs