Guard checkpointing on checkpoint_path or get_state_callback

Makes save_checkpoint a no-op when neither checkpoint_path nor
get_state_callback is provided. This avoids spurious checkpoint
errors in the Go engine where Spanner handles state persistence.

PiperOrigin-RevId: 975818621
Change-Id: I183e5f10ef2c44902dedb1ec5fd00876710415d7

Author: locross93

concordia/prefabs/simulation/generic.py

@@ -276,10 +276,13 @@ def play(
 
     self._get_state_callback = get_state_callback
 
-    checkpoint_callback = functools.partial(
-        # pyrefly: ignore [bad-argument-type]
-        self.save_checkpoint, checkpoint_path=checkpoint_path
-    )
+    if checkpoint_path or get_state_callback:
+      checkpoint_callback = functools.partial(
+          # pyrefly: ignore [bad-argument-type]
+          self.save_checkpoint, checkpoint_path=checkpoint_path
+      )
+    else:
+      checkpoint_callback = None
 
     # Ensure game masters are ordered Initializers first
     initializers = [
@@ -518,6 +521,9 @@ def set_component_dynamic_state(
 
   def save_checkpoint(self, step: int, checkpoint_path: str):
     """Saves the state of all entities at the current step."""
+    if not checkpoint_path and not self._get_state_callback:
+      return
+
     checkpoint_data = self.make_checkpoint_data()
 
     if self._get_state_callback: