Function transform_messages 

pub fn transform_messages(
    messages: &[Message],
    model: &Model,
    normalize_tool_call_id: Option<&NormalizeToolCallId<'_>>,
    now_ms: u64,
) -> Vec<Message>

Rewrites a transcript for model:

• images become placeholders when the model is text-only
• thinking from other models becomes text, or is dropped when empty or redacted
• tool-call ids from other models are normalized for the target API, given the id and its source message, and tool results follow
• failed and aborted assistant messages are dropped
• tool calls without a result get an error result before the next turn, and system messages between a call and its results move after the results