Function parse_messages_oaicompat 

pub fn parse_messages_oaicompat(
    messages_json: &str,
) -> Result<String, ChatError>

Validate and normalise an OpenAI-shaped messages array.

Expands the shorthands llama.cpp accepts — typed content parts, legacy function_call — into the canonical form, and rejects malformed input before it reaches a template.

Errors

Returns ChatError::BadJson if the input is not valid JSON, or ChatError::Failed if it is not a valid message array.