feat(core): strip message IDs from cache keys using model_copy

Author: aroun-coumar

libs/core/langchain_core/language_models/chat_models.py

@@ -1128,7 +1128,12 @@ def _generate_with_cache(
         if check_cache:
             if llm_cache:
                 llm_string = self._get_llm_string(stop=stop, **kwargs)
-                prompt = dumps(messages)
+                normalized_messages = [
+                    msg.model_copy(update={"id": None})
+                    if getattr(msg, "id", None) is not None else msg
+                    for msg in messages
+                ]
+                prompt = dumps(normalized_messages)
                 cache_val = llm_cache.lookup(prompt, llm_string)
                 if isinstance(cache_val, list):
                     converted_generations = self._convert_cached_generations(cache_val)