core: BaseChatModel modify chat message before passing to run_manager (…

…#19939)

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libs/core/langchain_core/language_models/chat_models.py

@@ -221,12 +221,12 @@ def stream(
             generation: Optional[ChatGenerationChunk] = None
             try:
                 for chunk in self._stream(messages, stop=stop, **kwargs):
-                    run_manager.on_llm_new_token(
-                        cast(str, chunk.message.content), chunk=chunk
-                    )
                     if chunk.message.id is None:
                         chunk.message.id = f"run-{run_manager.run_id}"
                     chunk.message.response_metadata = _gen_info_and_msg_metadata(chunk)
+                    run_manager.on_llm_new_token(
+                        cast(str, chunk.message.content), chunk=chunk
+                    )
                     yield chunk.message
                     if generation is None:
                         generation = chunk
@@ -293,12 +293,12 @@ async def astream(
                 stop=stop,
                 **kwargs,
             ):
-                await run_manager.on_llm_new_token(
-                    cast(str, chunk.message.content), chunk=chunk
-                )
                 if chunk.message.id is None:
                     chunk.message.id = f"run-{run_manager.run_id}"
                 chunk.message.response_metadata = _gen_info_and_msg_metadata(chunk)
+                await run_manager.on_llm_new_token(
+                    cast(str, chunk.message.content), chunk=chunk
+                )
                 yield chunk.message
                 if generation is None:
                     generation = chunk
@@ -610,13 +610,13 @@ def _generate_with_cache(
         ):
             chunks: List[ChatGenerationChunk] = []
             for chunk in self._stream(messages, stop=stop, **kwargs):
+                chunk.message.response_metadata = _gen_info_and_msg_metadata(chunk)
                 if run_manager:
                     if chunk.message.id is None:
                         chunk.message.id = f"run-{run_manager.run_id}"
                     run_manager.on_llm_new_token(
                         cast(str, chunk.message.content), chunk=chunk
                     )
-                chunk.message.response_metadata = _gen_info_and_msg_metadata(chunk)
                 chunks.append(chunk)
             result = generate_from_stream(iter(chunks))
         else:
@@ -691,13 +691,13 @@ async def _agenerate_with_cache(
         ):
             chunks: List[ChatGenerationChunk] = []
             async for chunk in self._astream(messages, stop=stop, **kwargs):
+                chunk.message.response_metadata = _gen_info_and_msg_metadata(chunk)
                 if run_manager:
                     if chunk.message.id is None:
                         chunk.message.id = f"run-{run_manager.run_id}"
                     await run_manager.on_llm_new_token(
                         cast(str, chunk.message.content), chunk=chunk
                     )
-                chunk.message.response_metadata = _gen_info_and_msg_metadata(chunk)
                 chunks.append(chunk)
             result = generate_from_stream(iter(chunks))
         else: