Function load_materialized_finished_turn_message 

pub fn load_materialized_finished_turn_message(
    session_id: &str,
) -> Result<Option<String>>

The answer a session’s last finished turn ended with.

This is what a finished child session reports back to the agent that delegated to it, so it has to be that turn’s own last agent message. The session-wide last agent message is not the same thing: a harness records messages of its own outside any turn, and a resume notice arriving after the child finished would then stand in for the child’s report.

None means the session has no projection row, or no finished turn whose span is recorded, and the caller decides what to show instead.