Function durable_chat_messages 

pub fn durable_chat_messages(
    history: &[ConversationMessage],
) -> Vec<ChatMessage>

Project a full agent conversation history down to the flat ChatMessage shape durable session backends store: user/assistant chat turns only, system prompt excluded (the backend restores against the caller’s own system prompt, not a persisted one). AssistantToolCalls and ToolResults are tool-loop plumbing that durable session transcripts have never persisted; only the visible chat turns are kept.

Callers that own the agent’s authoritative post-turn history (after budget-enforcement trimming) should use this to replace a durable transcript wholesale rather than appending the turn’s delta on top of a transcript the agent may have already trimmed underneath it.