Issue: validation error for AIMessage when run call to model with tools prefilled

[GuillermoGaete]

Issue you'd like to raise.

Hi! I am trying to reproduce my agent run in lang smith to debug my prompt.

https://smith.langchain.com/o/caa3b100-d0d0-4625-a557-282a455b05aa/playground/r/e2f9ec00-6c23-47b7-92b4-af84cd39dca1

I am getting the following error:

"1 validation error for AIMessage\ntype\n  Input should be 'ai' [type=literal_error, input_value='AIMessageChunk', input_type=str]\n    For further information visit https://errors.pydantic.dev/2.9/v/literal_error"

Suggestion:

No response