Any reasonable format will work. One of the great things about LLMs is they are very flexible on formats. Your suggested format of "Name: chat message\n" will work fine.
A good rule of thumb is that almost anything an average human can parse in a single linear pass can also be parsed by an LLM.
A good rule of thumb is that almost anything an average human can parse in a single linear pass can also be parsed by an LLM.