Function insert_request_messages_row 

pub async fn insert_request_messages_row(
    pool: &Pool,
    tier: Tier,
    response_id: &str,
    agent_instance_hierarchy: &str,
    timestamp: i64,
) -> Result<(), Error>

INSERT a objectiveai.messages row that registers this stream’s request blob in the agent’s history. Called once per (stream, agent) pair — the writer tracks which agents it has already seen and only emits this row the first time it encounters a new one in the row iterator. By postgres’s BIGSERIAL "index" assignment, this row is guaranteed to land earlier in the agent’s history than any subsequent streaming-content row that the same writer call sequences after it.